refactor: focus around Render/Compact/Pretty/NewWith functions

This is yet another drastic refactor of public API and concepts.
Hopefully the last one, as I'm now fairly happy with things.

binary.go

@@ -10,7 +10,10 @@ import (
 // interface.
 type Binary struct{}
 
-var _ FormatRenderer = (*Binary)(nil)
+var (
+	_ Handler        = (*Binary)(nil)
+	_ FormatsHandler = (*Binary)(nil)
+)
 
 // Render writes result of calling MarshalBinary() on v. If v does not implment
 // encoding.BinaryMarshaler the ErrCannotRander error will be returned.
@@ -33,6 +36,7 @@ func (br *Binary) Render(w io.Writer, v any) error {
 	return nil
 }
 
+// Formats returns a list of format strings that this Handler supports.
 func (br *Binary) Formats() []string {
 	return []string{"binary", "bin"}
 }

binary_test.go

@@ -78,3 +78,9 @@ func TestBinary_Render(t *testing.T) {
 		})
 	}
 }
+
+func TestBinary_Formats(t *testing.T) {
+	h := &Binary{}
+
+	assert.Equal(t, []string{"binary", "bin"}, h.Formats())
+}

interfaces.go

@@ -0,0 +1,41 @@
+package render
+
+import "io"
+
+// Handler interface is for single format renderers, which can only render a
+// single format. It is the basis of the multi-format support offerred by the
+// render package.
+type Handler interface {
+	// Render writes v into w in the format that the Handler supports.
+	//
+	// If v does not implement a required interface, or otherwise cannot be
+	// rendered to the format in question, then a ErrCannotRender error must be
+	// returned. Any other errors should be returned as is.
+	Render(w io.Writer, v any) error
+}
+
+// PrettyHandler interface is a optional interface that can be implemented by
+// Handler implementations to render a value in a pretty way. This is
+// useful for formats that support pretty printing, like in the case of JSON and
+// XML.
+type PrettyHandler interface {
+	// RenderPretty writes v into w in the format that the Handler supports,
+	// using a pretty variant of the format. The exact definition of "pretty" is
+	// up to the handler. Typically this would be mean adding line breaks and
+	// indentation, like in the case of JSON and XML.
+	//
+	// If v does not implement a required interface, or otherwise cannot be
+	// rendered to the format in question, then a ErrCannotRender error must be
+	// returned. Any other errors should be returned as is.
+	RenderPretty(w io.Writer, v any) error
+}
+
+// FormatsHandler is an optional interface that can be implemented by Handler
+// implementations to return a list of formats that the handler supports. This
+// is used by the New function to allow format aliases like "yml" for "yaml".
+type FormatsHandler interface {
+	// Formats returns a list of strings which all target the same format. In
+	// most cases this would just be a single value, but multiple values are
+	// supported for the sake of aliases, like "yaml" and "yml".
+	Formats() []string
+}

json.go

@@ -6,35 +6,48 @@ import (
 	"io"
 )
 
-// JSON is a renderer that marshals values to JSON.
+// JSONDefualtIndent is the default indentation string used by JSON instances
-type JSON struct {
+// when pretty rendering if no Indent value is set on the JSON instance itself.
-	// Pretty specifies whether the output should be pretty-printed. If true,
+var JSONDefualtIndent = "  "
-	// the output will be indented and newlines will be added.
-	Pretty bool
 
-	// Prefix is the prefix added to each level of indentation when Pretty is
+// JSON is a Handler that marshals values to JSON.
-	// true.
+type JSON struct {
+	// Prefix is the prefix added to each level of indentation when pretty
+	// rendering.
 	Prefix string
 
-	// Indent is the string added to each level of indentation when Pretty is
+	// Indent is the string added to each level of indentation when pretty
-	// true. If empty, two spaces will be used instead.
+	// rendering. If empty, two spaces will be used instead.
 	Indent string
 }
 
-var _ FormatRenderer = (*JSON)(nil)
+var (
+	_ Handler        = (*JSON)(nil)
+	_ PrettyHandler  = (*JSON)(nil)
+	_ FormatsHandler = (*JSON)(nil)
+)
 
 // Render marshals the given value to JSON.
 func (jr *JSON) Render(w io.Writer, v any) error {
-	enc := json.NewEncoder(w)
+	err := json.NewEncoder(w).Encode(v)
-	if jr.Pretty {
+	if err != nil {
+		return fmt.Errorf("%w: %w", ErrFailed, err)
+	}
+
+	return nil
+}
+
+// RenderPretty marshals the given value to JSON with line breaks and
+// indentation.
+func (jr *JSON) RenderPretty(w io.Writer, v any) error {
 	prefix := jr.Prefix
 	indent := jr.Indent
 	if indent == "" {
-			indent = "  "
+		indent = JSONDefualtIndent
 	}
 
+	enc := json.NewEncoder(w)
 	enc.SetIndent(prefix, indent)
-	}
 
 	err := enc.Encode(v)
 	if err != nil {
@@ -44,6 +57,7 @@ func (jr *JSON) Render(w io.Writer, v any) error {
 	return nil
 }
 
+// Formats returns a list of format strings that this Handler supports.
 func (jr *JSON) Formats() []string {
 	return []string{"json"}
 }

json_test.go

@@ -24,37 +24,21 @@ func (mjm *mockJSONMarshaler) MarshalJSON() ([]byte, error) {
 func TestJSON_Render(t *testing.T) {
 	tests := []struct {
 		name       string
-		pretty    bool
 		prefix     string
 		indent     string
-		value     interface{}
+		value      any
 		want       string
+		wantPretty string
 		wantErr    string
 		wantErrIs  []error
 	}{
 		{
-			name:   "simple object without pretty",
+			name:  "simple object",
-			pretty: false,
 			value: map[string]int{"age": 30},
 			want:  "{\"age\":30}\n",
 		},
 		{
-			name:   "simple object with pretty",
+			name:   "ignores prefix and indent",
-			pretty: true,
-			value:  map[string]int{"age": 30},
-			want:   "{\n  \"age\": 30\n}\n",
-		},
-		{
-			name:   "pretty with prefix and indent",
-			pretty: true,
-			prefix: "// ",
-			indent: "\t",
-			value:  map[string]int{"age": 30},
-			want:   "{\n// \t\"age\": 30\n// }\n",
-		},
-		{
-			name:   "prefix and indent without pretty",
-			pretty: false,
 			prefix: "// ",
 			indent: "\t",
 			value:  map[string]int{"age": 30},
@@ -72,7 +56,6 @@ func TestJSON_Render(t *testing.T) {
 		},
 		{
 			name:      "invalid value",
-			pretty:    false,
 			value:     make(chan int),
 			wantErr:   "render: failed: json: unsupported type: chan int",
 			wantErrIs: []error{Err, ErrFailed},
@@ -81,7 +64,6 @@ func TestJSON_Render(t *testing.T) {
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
 			j := &JSON{
-				Pretty: tt.pretty,
 				Prefix: tt.prefix,
 				Indent: tt.indent,
 			}
@@ -105,3 +87,76 @@ func TestJSON_Render(t *testing.T) {
 		})
 	}
 }
+
+func TestJSON_RenderPretty(t *testing.T) {
+	tests := []struct {
+		name       string
+		prefix     string
+		indent     string
+		value      any
+		want       string
+		wantPretty string
+		wantErr    string
+		wantErrIs  []error
+	}{
+		{
+			name:  "simple object",
+			value: map[string]int{"age": 30},
+			want:  "{\n  \"age\": 30\n}\n",
+		},
+		{
+			name:   "uses prefix and indent",
+			prefix: "// ",
+			indent: "\t",
+			value:  map[string]int{"age": 30},
+			want:   "{\n// \t\"age\": 30\n// }\n",
+		},
+		{
+			name:  "implements json.Marshaler",
+			value: &mockJSONMarshaler{data: []byte(`{"age":30}`)},
+			want:  "{\n  \"age\": 30\n}\n",
+		},
+		{
+			name:      "error from json.Marshaler",
+			value:     &mockJSONMarshaler{err: errors.New("marshal error!!1")},
+			wantErrIs: []error{Err, ErrFailed},
+		},
+		{
+			name:      "invalid value",
+			value:     make(chan int),
+			wantErr:   "render: failed: json: unsupported type: chan int",
+			wantErrIs: []error{Err, ErrFailed},
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			j := &JSON{
+				Prefix: tt.prefix,
+				Indent: tt.indent,
+			}
+			var buf bytes.Buffer
+
+			err := j.RenderPretty(&buf, tt.value)
+			got := buf.String()
+
+			if tt.wantErr != "" {
+				require.Error(t, err)
+				assert.EqualError(t, err, tt.wantErr)
+			}
+			for _, e := range tt.wantErrIs {
+				assert.ErrorIs(t, err, e)
+			}
+
+			if tt.wantErr == "" && len(tt.wantErrIs) == 0 {
+				require.NoError(t, err)
+				assert.Equal(t, tt.want, got)
+			}
+		})
+	}
+}
+
+func TestJSON_Formats(t *testing.T) {
+	h := &JSON{}
+
+	assert.Equal(t, []string{"json"}, h.Formats())
+}

multi.go

@@ -6,18 +6,22 @@ import (
 	"io"
 )
 
-// Multi is a renderer that tries multiple renderers until one succeeds.
+// Multi is a Handler that tries multiple handlers until one succeeds.
 type Multi struct {
-	Renderers []FormatRenderer
+	Handlers []Handler
 }
 
-var _ FormatRenderer = (*Multi)(nil)
+var (
+	_ Handler        = (*Multi)(nil)
+	_ PrettyHandler  = (*Multi)(nil)
+	_ FormatsHandler = (*Multi)(nil)
+)
 
-// Render tries each renderer in order until one succeeds. If none succeed,
+// Render tries each handler in order until one succeeds. If none succeed,
-// ErrCannotRender is returned. If a renderer returns an error that is not
+// ErrCannotRender is returned. If a handler returns an error that is not
 // ErrCannotRender, that error is returned.
 func (mr *Multi) Render(w io.Writer, v any) error {
-	for _, r := range mr.Renderers {
+	for _, r := range mr.Handlers {
 		err := r.Render(w, v)
 		if err == nil {
 			return nil
@@ -30,11 +34,37 @@ func (mr *Multi) Render(w io.Writer, v any) error {
 	return fmt.Errorf("%w: %T", ErrCannotRender, v)
 }
 
+// RenderPretty tries each handler in order until one succeeds. If none
+// succeed, ErrCannotRender is returned. If a handler returns an error that is
+// not ErrCannotRender, that error is returned.
+//
+// If a handler implements PrettyHandler, then the RenderPretty method is used
+// instead of Render. Otherwise, the Render method is used.
+func (mr *Multi) RenderPretty(w io.Writer, v any) error {
+	for _, r := range mr.Handlers {
+		var err error
+		if x, ok := r.(PrettyHandler); ok {
+			err = x.RenderPretty(w, v)
+		} else {
+			err = r.Render(w, v)
+		}
+		if err == nil {
+			return nil
+		}
+		if !errors.Is(err, ErrCannotRender) {
+			return err
+		}
+	}
+
+	return fmt.Errorf("%w: %T", ErrCannotRender, v)
+}
+
+// Formats returns a list of format strings that this Handler supports.
 func (mr *Multi) Formats() []string {
 	formats := make(map[string]struct{})
 
-	for _, r := range mr.Renderers {
+	for _, r := range mr.Handlers {
-		if x, ok := r.(Formats); ok {
+		if x, ok := r.(FormatsHandler); ok {
 			for _, f := range x.Formats() {
 				formats[f] = struct{}{}
 			}

multi_test.go

@@ -8,84 +8,129 @@ import (
 	"github.com/stretchr/testify/assert"
 )
 
-func TestMultiRenderer_Render(t *testing.T) {
+var multiHandlerTestCases = []struct {
-	successRenderer := &mockRenderer{output: "success output"}
-	cannotRenderer := &mockRenderer{err: ErrCannotRender}
-	failRenderer := &mockRenderer{err: errors.New("mock error")}
-
-	tests := []struct {
 	name       string
-		renderers []FormatRenderer
+	handlers   []Handler
-		value     interface{}
+	value      any
 	want       string
+	wantPretty string
 	wantErr    string
 	wantErrIs  []error
 }{
 	{
-			name: "no renderer can render",
+		name: "no handler can render",
-			renderers: []FormatRenderer{
+		handlers: []Handler{
-				cannotRenderer,
+			&mockHandler{err: ErrCannotRender},
-				cannotRenderer,
+			&mockHandler{err: ErrCannotRender},
 		},
 		value:     "test",
 		wantErr:   "render: cannot render: string",
 		wantErrIs: []error{ErrCannotRender},
 	},
 	{
-			name: "one renderer can render",
+		name: "one handler can render",
-			renderers: []FormatRenderer{
+		handlers: []Handler{
-				cannotRenderer,
+			&mockHandler{err: ErrCannotRender},
-				successRenderer,
+			&mockHandler{output: "success output"},
-				cannotRenderer,
+			&mockHandler{err: ErrCannotRender},
 		},
 		value:      struct{}{},
 		want:       "success output",
+		wantPretty: "success output",
 	},
 	{
-			name: "multiple renderers can render",
+		name: "one pretty handler can render",
-			renderers: []FormatRenderer{
+		handlers: []Handler{
-				&mockRenderer{err: ErrCannotRender},
+			&mockHandler{err: ErrCannotRender},
-				&mockRenderer{output: "first output"},
+			&mockPrettyHandler{
-				&mockRenderer{output: "second output"},
+				output:       "success output",
+				prettyOutput: "pretty success output",
+			},
+			&mockHandler{err: ErrCannotRender},
+		},
+		value:      struct{}{},
+		want:       "success output",
+		wantPretty: "pretty success output",
+	},
+	{
+		name: "multiple handlers can render",
+		handlers: []Handler{
+			&mockHandler{err: ErrCannotRender},
+			&mockHandler{output: "first output"},
+			&mockHandler{output: "second output"},
 		},
 		value:      struct{}{},
 		want:       "first output",
+		wantPretty: "first output",
 	},
 	{
-			name: "first renderer fails",
+		name: "multiple pretty handlers can render",
-			renderers: []FormatRenderer{
+		handlers: []Handler{
-				failRenderer,
+			&mockHandler{err: ErrCannotRender},
-				successRenderer,
+			&mockPrettyHandler{
+				output:       "first output",
+				prettyOutput: "pretty first output",
+			},
+			&mockPrettyHandler{
+				output:       "second output",
+				prettyOutput: "pretty second output",
+			},
+		},
+		value:      struct{}{},
+		want:       "first output",
+		wantPretty: "pretty first output",
+	},
+	{
+		name: "first handler fails",
+		handlers: []Handler{
+			&mockHandler{err: errors.New("mock error")},
+			&mockHandler{output: "success output"},
 		},
 		value:   struct{}{},
 		wantErr: "mock error",
 	},
 	{
 		name: "fails after cannot render",
-			renderers: []FormatRenderer{
+		handlers: []Handler{
-				cannotRenderer,
+			&mockHandler{err: ErrCannotRender},
-				failRenderer,
+			&mockHandler{err: errors.New("mock error")},
-				successRenderer,
+			&mockHandler{output: "success output"},
 		},
 		value:   struct{}{},
 		wantErr: "mock error",
 	},
 	{
 		name: "fails after success render",
-			renderers: []FormatRenderer{
+		handlers: []Handler{
-				successRenderer,
+			&mockHandler{output: "success output"},
-				failRenderer,
+			&mockHandler{err: errors.New("mock error")},
-				cannotRenderer,
+			&mockHandler{err: ErrCannotRender},
 		},
 		value:      struct{}{},
 		want:       "success output",
+		wantPretty: "success output",
+	},
+	{
+		name: "fails after success render with prettier handlers",
+		handlers: []Handler{
+			&mockPrettyHandler{
+				output:       "success output",
+				prettyOutput: "pretty success output",
+			},
+			&mockHandler{err: errors.New("mock error")},
+			&mockHandler{err: ErrCannotRender},
+		},
+		value:      struct{}{},
+		want:       "success output",
+		wantPretty: "pretty success output",
 	},
 }
 
-	for _, tt := range tests {
+func TestMulti_Render(t *testing.T) {
+	for _, tt := range multiHandlerTestCases {
 		t.Run(tt.name, func(t *testing.T) {
 			mr := &Multi{
-				Renderers: tt.renderers,
+				Handlers: tt.handlers,
 			}
 			var buf bytes.Buffer
 
@@ -106,3 +151,88 @@ func TestMultiRenderer_Render(t *testing.T) {
 		})
 	}
 }
+
+func TestMulti_RenderPretty(t *testing.T) {
+	for _, tt := range multiHandlerTestCases {
+		t.Run(tt.name, func(t *testing.T) {
+			mr := &Multi{
+				Handlers: tt.handlers,
+			}
+			var buf bytes.Buffer
+
+			err := mr.RenderPretty(&buf, tt.value)
+			got := buf.String()
+
+			if tt.wantErr != "" {
+				assert.EqualError(t, err, tt.wantErr)
+			}
+			for _, e := range tt.wantErrIs {
+				assert.ErrorIs(t, err, e)
+			}
+
+			if tt.wantErr == "" && len(tt.wantErrIs) == 0 {
+				assert.NoError(t, err)
+				assert.Equal(t, tt.wantPretty, got)
+			}
+		})
+	}
+}
+
+func TestMulti_Formats(t *testing.T) {
+	tests := []struct {
+		name     string
+		handlers []Handler
+		want     []string
+	}{
+		{
+			name: "single handler without a Formats method",
+			handlers: []Handler{
+				&mockHandler{},
+			},
+			want: []string{},
+		},
+		{
+			name: "multiple handlers without a Formats method",
+			handlers: []Handler{
+				&mockHandler{},
+			},
+			want: []string{},
+		},
+		{
+			name: "single handler with a Formats method",
+			handlers: []Handler{
+				&mockFormatsHandler{formats: []string{"yaml", "yml"}},
+			},
+			want: []string{"yaml", "yml"},
+		},
+		{
+			name: "multiple handlers without a Formats method",
+			handlers: []Handler{
+				&mockFormatsHandler{formats: []string{"yaml", "yml"}},
+				&mockFormatsHandler{formats: []string{"text", "txt"}},
+			},
+			want: []string{"yaml", "yml", "text", "txt"},
+		},
+		{
+			name: "mixture of handlers with and without a Formats method",
+			handlers: []Handler{
+				&mockFormatsHandler{formats: []string{"yaml", "yml"}},
+				&mockHandler{},
+				&mockFormatsHandler{formats: []string{"binary", "bin"}},
+				&mockHandler{},
+			},
+			want: []string{"yaml", "yml", "binary", "bin"},
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			mr := &Multi{
+				Handlers: tt.handlers,
+			}
+
+			got := mr.Formats()
+
+			assert.ElementsMatch(t, tt.want, got)
+		})
+	}
+}

render.go

@@ -1,14 +1,20 @@
 // Package render provides a simple and flexible way to render a value to a
 // io.Writer using different formats based on a format string argument.
 //
-// It allows rendering a custom type which can be marshaled to JSON, YAML, XML,
+// It is designed around using a custom type/struct to render your output.
-// while also supporting plain text by implementing fmt.Stringer or io.WriterTo.
+// Thanks to Go's marshaling interfaces, you get JSON, YAML, and XML support
-// Binary output is also supported by implementing the encoding.BinaryMarshaler
+// almost for free. While plain text output is supported by the type
-// interface.
+// implementing io.Reader, io.WriterTo, fmt.Stringer, or error interfaces, or by
+// simply being a type which can easily be type cast to a byte slice.
 //
 // Originally intended to easily implement CLI tools which can output their data
 // as plain text, as well as JSON/YAML with a simple switch of a format string.
 // But it can just as easily render to any io.Writer.
+//
+// The package is designed to be flexible and extensible with a sensible set of
+// defaults accessible via package level functions. You can create your own
+// Renderer for custom formats, or create new handlers that support custom
+// formats.
 package render
 
 import (
@@ -26,36 +32,11 @@ var (
 	// due to the value not supporting the format, or the value itself not being
 	// renderable. Only Renderer implementations should return this error.
 	ErrCannotRender = fmt.Errorf("%w: cannot render", Err)
-)
 
-// FormatRenderer interface is for single format renderers, which can only
+	// Base is a renderer that supports all formats. It is used by the package
-// render a single format.
+	// level NewWith function to create new renderers with a sub-set of
-type FormatRenderer interface {
+	// formats.
-	// Render writes v into w in the format that the FormatRenderer supports.
+	Base = New(map[string]Handler{
-	//
-	// If v does not implement a required interface, or otherwise cannot be
-	// rendered to the format in question, then a ErrCannotRender error must be
-	// returned. Any other errors should be returned as is.
-	Render(w io.Writer, v any) error
-}
-
-// Formats is an optional interface that can be implemented by FormatRenderer
-// implementations to return a list of formats that the renderer supports. This
-// is used by the NewRenderer function to allowing format aliases like "yml" for
-// "yaml".
-type Formats interface {
-	Formats() []string
-}
-
-var (
-	prettyRenderer = New(map[string]FormatRenderer{
-		"binary": &Binary{},
-		"json":   &JSON{Pretty: true},
-		"text":   &Text{},
-		"xml":    &XML{Pretty: true},
-		"yaml":   &YAML{Indent: 2},
-	})
-	compactRenderer = New(map[string]FormatRenderer{
 		"binary": &Binary{},
 		"json":   &JSON{},
 		"text":   &Text{},
@@ -63,110 +44,39 @@ var (
 		"yaml":   &YAML{},
 	})
 
-	DefaultPretty  = prettyRenderer.OnlyWith("json", "text", "xml", "yaml")
+	// Default is the default renderer that is used by package level Render,
-	DefaultCompact = compactRenderer.OnlyWith("json", "text", "xml", "yaml")
+	// Compact, Pretty functions. It supports JSON, Text, and YAML formats.
+	Default = Base.NewWith("json", "text", "yaml")
 )
 
-// Render renders the given value to the given writer using the given format.
+// Render renders the given value to the given writer using the given format. If
-// If pretty is true, the value will be rendered in a pretty way, otherwise it
+// pretty is true, the value will be rendered "pretty" if the target format
-// will be rendered in a compact way.
+// supports it, otherwise it will be rendered in a compact way.
 //
-// By default it supports the following formats:
+// It uses the default renderer to render the value, which supports JSON, Text,
+// and YAML formats out of the box.
 //
-//   - "text": Renders values via a myriad of ways.
+// If you need to support a custom set of formats, use the New function to
-//   - "json": Renders values using the encoding/json package.
+// create a new Renderer with the formats you need. If you need new custom
-//   - "yaml": Renders values using the gopkg.in/yaml.v3 package.
+// renderers, manually create a new Renderer.
-//   - "xml": Renders values using the encoding/xml package.
-//
-// If the format is not supported, a ErrUnsupportedFormat error will be
-// returned.
 func Render(w io.Writer, format string, pretty bool, v any) error {
-	if pretty {
+	return Default.Render(w, format, pretty, v)
-		return DefaultPretty.Render(w, format, v)
 }
 
-	return DefaultCompact.Render(w, format, v)
+// Compact is a convenience function that calls the Default renderer's Compact
-}
+// method. It is the same as calling Render with pretty set to false.
-
-// Pretty renders the given value to the given writer using the given format.
-// The format must be one of the formats supported by the default renderer.
-//
-// By default it supports the following formats:
-//
-//   - "text": Renders values via a myriad of ways.
-//   - "json": Renders values using the encoding/json package, with pretty
-//     printing enabled.
-//   - "yaml": Renders values using the gopkg.in/yaml.v3 package, with an
-//     indentation of 2 spaces.
-//   - "xml": Renders values using the encoding/xml package, with pretty
-//     printing enabled.
-//
-// If the format is not supported, a ErrUnsupportedFormat error will be
-// returned.
-//
-// If you need to support a custom set of formats, use the New function to
-// create a new Renderer with the formats you need. If you need new custom
-// renderers, manually create a new Renderer.
-func Pretty(w io.Writer, format string, v any) error {
-	return DefaultPretty.Render(w, format, v)
-}
-
-// Compact renders the given value to the given writer using the given format.
-// The format must be one of the formats supported by the default renderer.
-//
-// By default it supports the following formats:
-//
-//   - "text": Renders values via a myriad of ways..
-//   - "json": Renders values using the encoding/json package.
-//   - "yaml": Renders values using the gopkg.in/yaml.v3 package.
-//   - "xml": Renders values using the encoding/xml package.
-//
-// If the format is not supported, a ErrUnsupportedFormat error will be
-// returned.
-//
-// If you need to support a custom set of formats, use the New function to
-// create a new Renderer with the formats you need. If you need new custom
-// renderers, manually create a new Renderer.
 func Compact(w io.Writer, format string, v any) error {
-	return DefaultCompact.Render(w, format, v)
+	return Default.Compact(w, format, v)
 }
 
-// NewCompact returns a new renderer which only supports the specified formats
+// Pretty is a convenience function that calls the Default renderer's Pretty
-// and renders structured formats compactly. If no formats are specified, a
+// method. It is the same as calling Render with pretty set to true.
-// error is returned.
+func Pretty(w io.Writer, format string, v any) error {
-//
+	return Default.Pretty(w, format, v)
-// If any of the formats are not supported by, a ErrUnsupported error is
-// returned.
-func NewCompact(formats ...string) (*Renderer, error) {
-	if len(formats) == 0 {
-		return nil, fmt.Errorf("%w: no formats specified", Err)
 }
 
-	for _, format := range formats {
+// NewWith creates a new Renderer with the given formats. Only formats on the
-		if _, ok := compactRenderer.Renderers[format]; !ok {
+// BaseRender will be supported.
-			return nil, fmt.Errorf("%w: %s", ErrUnsupportedFormat, format)
+func NewWith(formats ...string) *Renderer {
-		}
+	return Base.NewWith(formats...)
-	}
-
-	return compactRenderer.OnlyWith(formats...), nil
-}
-
-// NewPretty returns a new renderer which only supports the specified formats
-// and renders structured formats in a pretty way. If no formats are specified,
-// a error is returned.
-//
-// If any of the formats are not supported by, a ErrUnsupported error is
-// returned.
-func NewPretty(formats ...string) (*Renderer, error) {
-	if len(formats) == 0 {
-		return nil, fmt.Errorf("%w: no formats specified", Err)
-	}
-
-	for _, format := range formats {
-		if _, ok := prettyRenderer.Renderers[format]; !ok {
-			return nil, fmt.Errorf("%w: %s", ErrUnsupportedFormat, format)
-		}
-	}
-
-	return prettyRenderer.OnlyWith(formats...), nil
 }

render_example_test.go

@@ -39,10 +39,7 @@ func ExampleRender_json() {
 	buf := &bytes.Buffer{}
 	err := render.Pretty(buf, "json", data)
 	if err != nil {
-		fmt.Printf("err: %s\n", err)
+		panic(err)
-
-		return
-		// panic(err)
 	}
 	fmt.Println(buf.String())
 
@@ -142,13 +139,13 @@ func ExampleRender_xml() {
 		Tags: []string{"golang", "json", "yaml", "toml"},
 	}
 
-	// Create a new renderer that supports XML in addition to default JSON, YAML
+	// Create a new renderer that supports XML in addition to the default JSON,
-	// and Text.
+	// Text, and YAML formats.
-	r, _ := render.NewPretty("json", "text", "xml", "yaml")
+	renderer := render.NewWith("json", "text", "xml", "yaml")
 
 	// Render the object to XML.
 	buf := &bytes.Buffer{}
-	err := r.Render(buf, "xml", data)
+	err := renderer.Pretty(buf, "xml", data)
 	if err != nil {
 		panic(err)
 	}

render_test.go

@@ -30,23 +30,93 @@ func (mw *mockWriter) String() string {
 	return mw.buf.String()
 }
 
-type mockRenderer struct {
+type mockHandler struct {
 	output  string
+	formats []string
 	err     error
 }
 
-var _ FormatRenderer = (*mockRenderer)(nil)
+var (
+	_ Handler        = (*mockHandler)(nil)
+	_ FormatsHandler = (*mockHandler)(nil)
+)
 
-func (m *mockRenderer) Render(w io.Writer, _ any) error {
+func (mh *mockHandler) Render(w io.Writer, _ any) error {
-	_, err := w.Write([]byte(m.output))
+	_, err := w.Write([]byte(mh.output))
 
-	if m.err != nil {
+	if mh.err != nil {
-		return m.err
+		return mh.err
 	}
 
 	return err
 }
 
+func (mh *mockHandler) Formats() []string {
+	return mh.formats
+}
+
+type mockPrettyHandler struct {
+	output       string
+	prettyOutput string
+	formats      []string
+	err          error
+}
+
+var (
+	_ Handler        = (*mockPrettyHandler)(nil)
+	_ PrettyHandler  = (*mockPrettyHandler)(nil)
+	_ FormatsHandler = (*mockPrettyHandler)(nil)
+)
+
+func (mph *mockPrettyHandler) Render(w io.Writer, _ any) error {
+	_, err := w.Write([]byte(mph.output))
+
+	if mph.err != nil {
+		return mph.err
+	}
+
+	return err
+}
+
+func (mph *mockPrettyHandler) RenderPretty(w io.Writer, _ any) error {
+	_, err := w.Write([]byte(mph.prettyOutput))
+
+	if mph.err != nil {
+		return mph.err
+	}
+
+	return err
+}
+
+func (mph *mockPrettyHandler) Formats() []string {
+	return mph.formats
+}
+
+type mockFormatsHandler struct {
+	output  string
+	formats []string
+	err     error
+}
+
+var (
+	_ Handler        = (*mockFormatsHandler)(nil)
+	_ FormatsHandler = (*mockFormatsHandler)(nil)
+)
+
+func (mph *mockFormatsHandler) Render(w io.Writer, _ any) error {
+	_, err := w.Write([]byte(mph.output))
+
+	if mph.err != nil {
+		return mph.err
+	}
+
+	return err
+}
+
+func (mph *mockFormatsHandler) Formats() []string {
+	return mph.formats
+}
+
 type renderFormatTestCase struct {
 	name        string
 	writeErr    error
@@ -69,6 +139,12 @@ var binaryFormattestCases = []renderFormatTestCase{
 		value:   &mockBinaryMarshaler{data: []byte("test string")},
 		want:    "test string",
 	},
+	{
+		name:    "capitalized format",
+		formats: []string{"BINARY", "BIN"},
+		value:   &mockBinaryMarshaler{data: []byte("test string")},
+		want:    "test string",
+	},
 	{
 		name:      "without binary marshaler",
 		formats:   []string{"binary", "bin"},
@@ -112,6 +188,13 @@ var jsonFormatTestCases = []renderFormatTestCase{
 		wantPretty:  "{\n  \"age\": 30\n}\n",
 		wantCompact: "{\"age\":30}\n",
 	},
+	{
+		name:        "capitalized format",
+		formats:     []string{"JSON"},
+		value:       map[string]int{"age": 30},
+		wantPretty:  "{\n  \"age\": 30\n}\n",
+		wantCompact: "{\"age\":30}\n",
+	},
 	{
 		name:        "with json marshaler",
 		formats:     []string{"json"},
@@ -151,6 +234,12 @@ var textFormatTestCases = []renderFormatTestCase{
 		wantErr:   "render: unsupported format: {{format}}",
 		wantErrIs: []error{Err, ErrUnsupportedFormat},
 	},
+	{
+		name:    "capitalized format",
+		formats: []string{"TEXT", "TXT", "PLAIN"},
+		value:   []byte("test byte slice"),
+		want:    "test byte slice",
+	},
 	{
 		name:    "byte slice",
 		formats: []string{"text", "txt", "plain"},
@@ -344,6 +433,12 @@ var xmlFormatTestCases = []renderFormatTestCase{
 		value:   &mockXMLMarshaler{elm: "test string"},
 		want:    "<mockXMLMarshaler>test string</mockXMLMarshaler>",
 	},
+	{
+		name:    "capitalized format",
+		formats: []string{"XML"},
+		value:   &mockXMLMarshaler{elm: "test string"},
+		want:    "<mockXMLMarshaler>test string</mockXMLMarshaler>",
+	},
 	{
 		name:      "xml format with error from xml.Marshaler",
 		formats:   []string{"xml"},
@@ -379,6 +474,12 @@ var yamlFormatTestCases = []renderFormatTestCase{
 		value:   map[string]int{"age": 30},
 		want:    "age: 30\n",
 	},
+	{
+		name:    "capitalized format",
+		formats: []string{"YAML", "YML"},
+		value:   map[string]int{"age": 30},
+		want:    "age: 30\n",
+	},
 	{
 		name:    "yaml format with nested structure",
 		formats: []string{"yaml", "yml"},
@@ -419,6 +520,72 @@ var yamlFormatTestCases = []renderFormatTestCase{
 	},
 }
 
+func TestRender(t *testing.T) {
+	tests := []renderFormatTestCase{}
+	tests = append(tests, jsonFormatTestCases...)
+	tests = append(tests, textFormatTestCases...)
+	tests = append(tests, yamlFormatTestCases...)
+
+	for _, tt := range tests {
+		for _, pretty := range []bool{false, true} {
+			for _, format := range tt.formats {
+				name := format + " format " + tt.name
+				if pretty {
+					name = "pretty " + name
+				}
+
+				t.Run(name, func(t *testing.T) {
+					w := &mockWriter{WriteErr: tt.writeErr}
+
+					value := tt.value
+					if tt.valueFunc != nil {
+						value = tt.valueFunc()
+					}
+
+					var err error
+					var panicRes any
+					func() {
+						defer func() {
+							if r := recover(); r != nil {
+								panicRes = r
+							}
+						}()
+						err = Render(w, format, pretty, value)
+					}()
+
+					got := w.String()
+					want := tt.want
+					if pretty && tt.wantPretty != "" {
+						want = tt.wantPretty
+					} else if tt.wantCompact != "" {
+						want = tt.wantCompact
+					}
+
+					if tt.wantPanic != "" {
+						assert.Equal(t, tt.wantPanic, panicRes)
+					}
+
+					if tt.wantErr != "" {
+						wantErr := strings.ReplaceAll(
+							tt.wantErr, "{{format}}", format,
+						)
+						assert.EqualError(t, err, wantErr)
+					}
+					for _, e := range tt.wantErrIs {
+						assert.ErrorIs(t, err, e)
+					}
+
+					if tt.wantPanic == "" &&
+						tt.wantErr == "" && len(tt.wantErrIs) == 0 {
+						assert.NoError(t, err)
+						assert.Equal(t, want, got)
+					}
+				})
+			}
+		}
+	}
+}
+
 func TestPretty(t *testing.T) {
 	tests := []renderFormatTestCase{}
 	tests = append(tests, jsonFormatTestCases...)
@@ -536,3 +703,86 @@ func TestCompact(t *testing.T) {
 		}
 	}
 }
+
+func TestNewWith(t *testing.T) {
+	tests := []struct {
+		name    string
+		formats []string
+		want    *Renderer
+	}{
+		{
+			name:    "no formats",
+			formats: nil,
+			want: &Renderer{
+				Handlers: map[string]Handler{},
+			},
+		},
+		{
+			name:    "single format",
+			formats: []string{"json"},
+			want: &Renderer{
+				Handlers: map[string]Handler{
+					"json": &JSON{},
+				},
+			},
+		},
+		{
+			name:    "multiple formats",
+			formats: []string{"json", "xml"},
+			want: &Renderer{
+				Handlers: map[string]Handler{
+					"json": &JSON{},
+					"xml":  &XML{},
+				},
+			},
+		},
+		{
+			name:    "multiple formats with aliases",
+			formats: []string{"yaml", "text", "binary"},
+			want: &Renderer{
+				Handlers: map[string]Handler{
+					"bin":    &Binary{},
+					"binary": &Binary{},
+					"plain":  &Text{},
+					"text":   &Text{},
+					"txt":    &Text{},
+					"yaml":   &YAML{},
+					"yml":    &YAML{},
+				},
+			},
+		},
+		{
+			name:    "duplicate formats",
+			formats: []string{"json", "json", "yaml", "yaml"},
+			want: &Renderer{
+				Handlers: map[string]Handler{
+					"json": &JSON{},
+					"yaml": &YAML{},
+					"yml":  &YAML{},
+				},
+			},
+		},
+		{
+			name:    "capitalized formats",
+			formats: []string{"YAML", "TEXT", "BINARY"},
+			want: &Renderer{
+				Handlers: map[string]Handler{
+					"bin":    &Binary{},
+					"binary": &Binary{},
+					"plain":  &Text{},
+					"text":   &Text{},
+					"txt":    &Text{},
+					"yaml":   &YAML{},
+					"yml":    &YAML{},
+				},
+			},
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got := NewWith(tt.formats...)
+
+			assert.Equal(t, tt.want, got)
+		})
+	}
+}

renderer.go

@@ -4,61 +4,86 @@ import (
 	"errors"
 	"fmt"
 	"io"
+	"strings"
 )
 
-// ErrUnsupportedFormat is returned when a format is not supported by a
+// ErrUnsupportedFormat is returned when a format is not supported by any
-// renderer. Any method that accepts a format string may return this error.
+// Handler.
 var ErrUnsupportedFormat = fmt.Errorf("%w: unsupported format", Err)
 
-// Renderer is a renderer that delegates rendering to another renderer
+// Renderer exposes methods for rendering values to different formats. The
-// based on a format value.
+// Renderer delegates rendering to format specific handlers based on the format
+// string given.
 type Renderer struct {
-	// Renderers is a map of format names to renderers. When Render is called,
+	// Handlers is a map of format names to Handler. When Render is called,
-	// the format is used to look up the renderer to use.
+	// the format is used to look up the Handler to use.
-	Renderers map[string]FormatRenderer
+	Handlers map[string]Handler
 }
 
 // New returns a new Renderer that delegates rendering to the specified
-// renderers.
+// Handlers.
 //
-// Any renderers which implement the Formats interface, will also be set as the
+// Any Handlers which implement the FormatsHandler interface, will also be set
-// renderer for all format strings returned by Format() on the renderer.
+// as the handler for all format strings returned by Formats() on the handler.
-func New(renderers map[string]FormatRenderer) *Renderer {
+func New(handlers map[string]Handler) *Renderer {
-	newRenderers := make(map[string]FormatRenderer, len(renderers))
+	r := &Renderer{Handlers: make(map[string]Handler, len(handlers))}
 
-	for format, r := range renderers {
+	for format, handler := range handlers {
-		newRenderers[format] = r
+		r.Add(format, handler)
+	}
 
-		if x, ok := r.(Formats); ok {
+	return r
+}
+
+// Add adds a Handler to the Renderer. If the handler implements the
+// FormatsHandler interface, the handler will be added for all formats returned
+// by Formats().
+func (r *Renderer) Add(format string, handler Handler) {
+	if format != "" {
+		r.Handlers[strings.ToLower(format)] = handler
+	}
+
+	if x, ok := handler.(FormatsHandler); ok {
 		for _, f := range x.Formats() {
-				if f != format {
+			if f != "" && f != format {
-					newRenderers[f] = r
+				r.Handlers[strings.ToLower(f)] = handler
 			}
 		}
 	}
 }
 
-	return &Renderer{Renderers: newRenderers}
+// Render renders a value to the given io.Writer using the specified format.
-}
-
-// Render renders a value to an io.Writer using the specified format. If the
-// format is not supported, ErrUnsupportedFormat is returned.
 //
-// If the format is supported, but the value cannot be rendered to the format,
+// If pretty is true, it will attempt to render the value with pretty
-// the error returned by the renderer is returned. In most cases this will be
+// formatting if the underlying Handler supports pretty formatting.
-// ErrCannotRender, but it could be a different error if the renderer returns
+//
-// one.
+// If the format is not supported or the value cannot be rendered to the format,
-func (r *Renderer) Render(w io.Writer, format string, v any) error {
+// a ErrUnsupportedFormat error is returned.
-	renderer, ok := r.Renderers[format]
+func (r *Renderer) Render(
+	w io.Writer,
+	format string,
+	pretty bool,
+	v any,
+) error {
+	handler, ok := r.Handlers[strings.ToLower(format)]
 	if !ok {
 		return fmt.Errorf("%w: %s", ErrUnsupportedFormat, format)
 	}
 
-	err := renderer.Render(w, v)
+	prettyHandler, ok := handler.(PrettyHandler)
+	var err error
+	if pretty && ok {
+		err = prettyHandler.RenderPretty(w, v)
+	} else {
+		err = handler.Render(w, v)
+	}
+
 	if err != nil {
 		if errors.Is(err, ErrCannotRender) {
 			return fmt.Errorf("%w: %s", ErrUnsupportedFormat, format)
 		}
+
+		// Ensure that the error is wrapped with ErrFailed if it is not already.
 		if !errors.Is(err, ErrFailed) {
 			return fmt.Errorf("%w: %w", ErrFailed, err)
 		}
@@ -69,14 +94,27 @@ func (r *Renderer) Render(w io.Writer, format string, v any) error {
 	return nil
 }
 
-func (r *Renderer) OnlyWith(formats ...string) *Renderer {
+// Compact is a convenience method that calls Render with pretty set to false.
-	renderers := make(map[string]FormatRenderer, len(formats))
+func (r *Renderer) Compact(w io.Writer, format string, v any) error {
+	return r.Render(w, format, false, v)
+}
+
+// Pretty is a convenience method that calls Render with pretty set to true.
+func (r *Renderer) Pretty(w io.Writer, format string, v any) error {
+	return r.Render(w, format, true, v)
+}
+
+// NewWith creates a new Renderer with the formats given, if they have handlers
+// in the currener Renderer. It essentially allows to restrict a Renderer to a
+// only a sub-set of supported formats.
+func (r *Renderer) NewWith(formats ...string) *Renderer {
+	handlers := make(map[string]Handler, len(formats))
 
 	for _, format := range formats {
-		if r, ok := r.Renderers[format]; ok {
+		if r, ok := r.Handlers[strings.ToLower(format)]; ok {
-			renderers[format] = r
+			handlers[format] = r
 		}
 	}
 
-	return New(renderers)
+	return New(handlers)
 }

renderer_test.go

@@ -8,32 +8,230 @@ import (
 	"testing"
 
 	"github.com/stretchr/testify/assert"
-	"github.com/stretchr/testify/require"
 )
 
+func TestNew(t *testing.T) {
+	tests := []struct {
+		name     string
+		handlers map[string]Handler
+		want     *Renderer
+	}{
+		{
+			name: "nil handlers map",
+			want: &Renderer{Handlers: map[string]Handler{}},
+		},
+		{
+			name:     "empty handlers map",
+			handlers: map[string]Handler{},
+			want:     &Renderer{Handlers: map[string]Handler{}},
+		},
+		{
+			name: "single handler",
+			handlers: map[string]Handler{
+				"mock": &mockHandler{},
+			},
+			want: &Renderer{Handlers: map[string]Handler{
+				"mock": &mockHandler{},
+			}},
+		},
+		{
+			name: "multiple handlers",
+			handlers: map[string]Handler{
+				"mock":  &mockHandler{},
+				"other": &mockHandler{output: "other output"},
+			},
+			want: &Renderer{Handlers: map[string]Handler{
+				"mock":  &mockHandler{},
+				"other": &mockHandler{output: "other output"},
+			}},
+		},
+		{
+			name: "multiple handlers with alias formats",
+			handlers: map[string]Handler{
+				"mock":  &mockFormatsHandler{formats: []string{"mock", "m"}},
+				"other": &mockFormatsHandler{formats: []string{"other", "o"}},
+			},
+			want: &Renderer{Handlers: map[string]Handler{
+				"mock":  &mockFormatsHandler{formats: []string{"mock", "m"}},
+				"m":     &mockFormatsHandler{formats: []string{"mock", "m"}},
+				"other": &mockFormatsHandler{formats: []string{"other", "o"}},
+				"o":     &mockFormatsHandler{formats: []string{"other", "o"}},
+			}},
+		},
+		{
+			name: "multiple handlers with custom formats",
+			handlers: map[string]Handler{
+				"foo": &mockFormatsHandler{formats: []string{"mock", "m"}},
+				"bar": &mockFormatsHandler{formats: []string{"other", "o"}},
+			},
+			want: &Renderer{Handlers: map[string]Handler{
+				"foo":   &mockFormatsHandler{formats: []string{"mock", "m"}},
+				"mock":  &mockFormatsHandler{formats: []string{"mock", "m"}},
+				"m":     &mockFormatsHandler{formats: []string{"mock", "m"}},
+				"bar":   &mockFormatsHandler{formats: []string{"other", "o"}},
+				"other": &mockFormatsHandler{formats: []string{"other", "o"}},
+				"o":     &mockFormatsHandler{formats: []string{"other", "o"}},
+			}},
+		},
+		{
+			name: "multiple handlers with capitalized formats",
+			handlers: map[string]Handler{
+				"Foo": &mockFormatsHandler{formats: []string{"MOCK", "m"}},
+				"Bar": &mockFormatsHandler{formats: []string{"OTHER", "o"}},
+			},
+			want: &Renderer{Handlers: map[string]Handler{
+				"foo":   &mockFormatsHandler{formats: []string{"MOCK", "m"}},
+				"mock":  &mockFormatsHandler{formats: []string{"MOCK", "m"}},
+				"m":     &mockFormatsHandler{formats: []string{"MOCK", "m"}},
+				"bar":   &mockFormatsHandler{formats: []string{"OTHER", "o"}},
+				"other": &mockFormatsHandler{formats: []string{"OTHER", "o"}},
+				"o":     &mockFormatsHandler{formats: []string{"OTHER", "o"}},
+			}},
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got := New(tt.handlers)
+
+			assert.Equal(t, tt.want, got)
+		})
+	}
+}
+
+func TestRenderer_Add(t *testing.T) {
+	tests := []struct {
+		name    string
+		format  string
+		handler Handler
+		want    []string
+	}{
+		{
+			name:    "handler without Formats",
+			format:  "tackle",
+			handler: &mockHandler{},
+			want:    []string{"tackle"},
+		},
+		{
+			name:    "hander with Formats",
+			format:  "hackle",
+			handler: &mockFormatsHandler{formats: []string{"hackle"}},
+			want:    []string{"hackle"},
+		},
+		{
+			name:    "hander with alias formats",
+			format:  "hackle",
+			handler: &mockFormatsHandler{formats: []string{"hackle", "hack"}},
+			want:    []string{"hackle", "hack"},
+		},
+		{
+			name:    "given format differs from Formats",
+			format:  "foobar",
+			handler: &mockFormatsHandler{formats: []string{"hackle", "hack"}},
+			want:    []string{"foobar", "hackle", "hack"},
+		},
+		{
+			name:    "lowercases capitalized formats",
+			format:  "FooBar",
+			handler: &mockFormatsHandler{formats: []string{"HACKLE", "Hack"}},
+			want:    []string{"foobar", "hackle", "hack"},
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			r := &Renderer{Handlers: map[string]Handler{}}
+
+			r.Add(tt.format, tt.handler)
+
+			for _, f := range tt.want {
+				got, ok := r.Handlers[f]
+				assert.Truef(t, ok, "not added as %q format", f)
+				assert.Equal(t, tt.handler, got)
+			}
+
+			gotFormats := []string{}
+			for f := range r.Handlers {
+				gotFormats = append(gotFormats, f)
+			}
+			assert.ElementsMatch(t, tt.want, gotFormats)
+		})
+	}
+}
+
 func TestRenderer_Render(t *testing.T) {
 	tests := []struct {
 		name      string
-		renderers map[string]FormatRenderer
+		handlers  map[string]Handler
 		format    string
-		value     interface{}
+		pretty    bool
+		value     any
 		want      string
 		wantErr   string
 		wantErrIs []error
 	}{
 		{
-			name: "existing renderer",
+			name: "no pretty with handler that supports pretty",
-			renderers: map[string]FormatRenderer{
+			handlers: map[string]Handler{
-				"mock": &mockRenderer{output: "mock output"},
+				"mock": &mockPrettyHandler{
+					output:       "plain output",
+					prettyOutput: "pretty output",
+				},
 			},
 			format: "mock",
+			pretty: false,
 			value:  struct{}{},
-			want:   "mock output",
+			want:   "plain output",
 		},
 		{
-			name: "existing renderer returns error",
+			name: "no pretty with handler that does not support pretty",
-			renderers: map[string]FormatRenderer{
+			handlers: map[string]Handler{
-				"other": &mockRenderer{
+				"mock": &mockHandler{output: "plain output"},
+			},
+			format: "mock",
+			pretty: false,
+			value:  struct{}{},
+			want:   "plain output",
+		},
+		{
+			name: "pretty with handler that supports pretty",
+			handlers: map[string]Handler{
+				"mock": &mockPrettyHandler{
+					output:       "plain output",
+					prettyOutput: "pretty output",
+				},
+			},
+			format: "mock",
+			pretty: true,
+			value:  struct{}{},
+			want:   "pretty output",
+		},
+		{
+			name: "pretty with handler that does not support pretty",
+			handlers: map[string]Handler{
+				"mock": &mockHandler{
+					output: "plain output",
+				},
+			},
+			format: "mock",
+			pretty: true,
+			value:  struct{}{},
+			want:   "plain output",
+		},
+		{
+			name: "normalizes given format to lowercase",
+			handlers: map[string]Handler{
+				"mock": &mockHandler{
+					output: "plain output",
+				},
+			},
+			format: "MOCK",
+			pretty: true,
+			value:  struct{}{},
+			want:   "plain output",
+		},
+		{
+			name: "handler returns error",
+			handlers: map[string]Handler{
+				"other": &mockHandler{
 					output: "mock output",
 					err:    errors.New("mock error"),
 				},
@@ -43,9 +241,9 @@ func TestRenderer_Render(t *testing.T) {
 			wantErr: "render: failed: mock error",
 		},
 		{
-			name: "existing renderer returns ErrCannotRender",
+			name: "handler returns ErrCannotRender",
-			renderers: map[string]FormatRenderer{
+			handlers: map[string]Handler{
-				"other": &mockRenderer{
+				"other": &mockHandler{
 					output: "mock output",
 					err:    fmt.Errorf("%w: mock", ErrCannotRender),
 				},
@@ -56,8 +254,8 @@ func TestRenderer_Render(t *testing.T) {
 			wantErrIs: []error{Err, ErrUnsupportedFormat},
 		},
 		{
-			name:      "non-existing renderer",
+			name:      "non-existing handler",
-			renderers: map[string]FormatRenderer{},
+			handlers:  map[string]Handler{},
 			format:    "unknown",
 			value:     struct{}{},
 			wantErr:   "render: unsupported format: unknown",
@@ -66,12 +264,194 @@ func TestRenderer_Render(t *testing.T) {
 	}
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
-			fr := &Renderer{
+			r := &Renderer{
-				Renderers: tt.renderers,
+				Handlers: tt.handlers,
 			}
 			var buf bytes.Buffer
 
-			err := fr.Render(&buf, tt.format, tt.value)
+			err := r.Render(&buf, tt.format, tt.pretty, tt.value)
+			got := buf.String()
+
+			if tt.wantErr != "" {
+				assert.EqualError(t, err, tt.wantErr)
+			}
+			for _, e := range tt.wantErrIs {
+				assert.ErrorIs(t, err, e)
+			}
+
+			if tt.wantErr == "" && len(tt.wantErrIs) == 0 {
+				assert.NoError(t, err)
+				assert.Equal(t, tt.want, got)
+			}
+		})
+	}
+}
+
+func TestRenderer_Compact(t *testing.T) {
+	tests := []struct {
+		name      string
+		handlers  map[string]Handler
+		format    string
+		value     any
+		want      string
+		wantErr   string
+		wantErrIs []error
+	}{
+		{
+			name: "handler supports pretty",
+			handlers: map[string]Handler{
+				"mock": &mockPrettyHandler{
+					output:       "plain output",
+					prettyOutput: "pretty output",
+				},
+			},
+			format: "mock",
+			value:  struct{}{},
+			want:   "plain output",
+		},
+		{
+			name: "handler does not support pretty",
+			handlers: map[string]Handler{
+				"mock": &mockHandler{output: "plain output"},
+			},
+			format: "mock",
+			value:  struct{}{},
+			want:   "plain output",
+		},
+		{
+			name: "handler returns error",
+			handlers: map[string]Handler{
+				"other": &mockHandler{
+					output: "mock output",
+					err:    errors.New("mock error"),
+				},
+			},
+			format:  "other",
+			value:   struct{}{},
+			wantErr: "render: failed: mock error",
+		},
+		{
+			name: "handler returns ErrCannotRender",
+			handlers: map[string]Handler{
+				"other": &mockHandler{
+					output: "mock output",
+					err:    fmt.Errorf("%w: mock", ErrCannotRender),
+				},
+			},
+			format:    "other",
+			value:     struct{}{},
+			wantErr:   "render: unsupported format: other",
+			wantErrIs: []error{Err, ErrUnsupportedFormat},
+		},
+		{
+			name:      "non-existing handler",
+			handlers:  map[string]Handler{},
+			format:    "unknown",
+			value:     struct{}{},
+			wantErr:   "render: unsupported format: unknown",
+			wantErrIs: []error{Err, ErrUnsupportedFormat},
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			r := &Renderer{
+				Handlers: tt.handlers,
+			}
+			var buf bytes.Buffer
+
+			err := r.Compact(&buf, tt.format, tt.value)
+			got := buf.String()
+
+			if tt.wantErr != "" {
+				assert.EqualError(t, err, tt.wantErr)
+			}
+			for _, e := range tt.wantErrIs {
+				assert.ErrorIs(t, err, e)
+			}
+
+			if tt.wantErr == "" && len(tt.wantErrIs) == 0 {
+				assert.NoError(t, err)
+				assert.Equal(t, tt.want, got)
+			}
+		})
+	}
+}
+
+func TestRenderer_Pretty(t *testing.T) {
+	tests := []struct {
+		name      string
+		handlers  map[string]Handler
+		format    string
+		value     any
+		want      string
+		wantErr   string
+		wantErrIs []error
+	}{
+		{
+			name: "handler supports pretty",
+			handlers: map[string]Handler{
+				"mock": &mockPrettyHandler{
+					output:       "plain output",
+					prettyOutput: "pretty output",
+				},
+			},
+			format: "mock",
+			value:  struct{}{},
+			want:   "pretty output",
+		},
+		{
+			name: "handler does not support pretty",
+			handlers: map[string]Handler{
+				"mock": &mockHandler{
+					output: "plain output",
+				},
+			},
+			format: "mock",
+			value:  struct{}{},
+			want:   "plain output",
+		},
+		{
+			name: "handler returns error",
+			handlers: map[string]Handler{
+				"other": &mockHandler{
+					output: "mock output",
+					err:    errors.New("mock error"),
+				},
+			},
+			format:  "other",
+			value:   struct{}{},
+			wantErr: "render: failed: mock error",
+		},
+		{
+			name: "handler returns ErrCannotRender",
+			handlers: map[string]Handler{
+				"other": &mockHandler{
+					output: "mock output",
+					err:    fmt.Errorf("%w: mock", ErrCannotRender),
+				},
+			},
+			format:    "other",
+			value:     struct{}{},
+			wantErr:   "render: unsupported format: other",
+			wantErrIs: []error{Err, ErrUnsupportedFormat},
+		},
+		{
+			name:      "non-existing handler",
+			handlers:  map[string]Handler{},
+			format:    "unknown",
+			value:     struct{}{},
+			wantErr:   "render: unsupported format: unknown",
+			wantErrIs: []error{Err, ErrUnsupportedFormat},
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			r := &Renderer{
+				Handlers: tt.handlers,
+			}
+			var buf bytes.Buffer
+
+			err := r.Pretty(&buf, tt.format, tt.value)
 			got := buf.String()
 
 			if tt.wantErr != "" {
@@ -97,6 +477,75 @@ func TestRenderer_RenderAllFormats(t *testing.T) {
 	tests = append(tests, xmlFormatTestCases...)
 	tests = append(tests, yamlFormatTestCases...)
 
+	for _, tt := range tests {
+		for _, pretty := range []bool{false, true} {
+			for _, format := range tt.formats {
+				name := format + " format " + tt.name
+				if pretty {
+					name = "pretty " + name
+				}
+
+				t.Run(name, func(t *testing.T) {
+					w := &mockWriter{WriteErr: tt.writeErr}
+
+					value := tt.value
+					if tt.valueFunc != nil {
+						value = tt.valueFunc()
+					}
+
+					var err error
+					var panicRes any
+
+					func() {
+						defer func() {
+							if r := recover(); r != nil {
+								panicRes = r
+							}
+						}()
+						err = Base.Render(w, format, pretty, value)
+					}()
+
+					got := w.String()
+					want := tt.want
+					if pretty && tt.wantPretty != "" {
+						want = tt.wantPretty
+					} else if tt.wantCompact != "" {
+						want = tt.wantCompact
+					}
+
+					if tt.wantPanic != "" {
+						assert.Equal(t, tt.wantPanic, panicRes)
+					}
+
+					if tt.wantErr != "" {
+						wantErr := strings.ReplaceAll(
+							tt.wantErr, "{{format}}", format,
+						)
+						assert.EqualError(t, err, wantErr)
+					}
+					for _, e := range tt.wantErrIs {
+						assert.ErrorIs(t, err, e)
+					}
+
+					if tt.wantPanic == "" &&
+						tt.wantErr == "" && len(tt.wantErrIs) == 0 {
+						assert.NoError(t, err)
+						assert.Equal(t, want, got)
+					}
+				})
+			}
+		}
+	}
+}
+
+func TestRenderer_CompactAllFormats(t *testing.T) {
+	tests := []renderFormatTestCase{}
+	tests = append(tests, binaryFormattestCases...)
+	tests = append(tests, jsonFormatTestCases...)
+	tests = append(tests, textFormatTestCases...)
+	tests = append(tests, xmlFormatTestCases...)
+	tests = append(tests, yamlFormatTestCases...)
+
 	for _, tt := range tests {
 		for _, format := range tt.formats {
 			t.Run(format+" format "+tt.name, func(t *testing.T) {
@@ -109,8 +558,6 @@ func TestRenderer_RenderAllFormats(t *testing.T) {
 
 				var err error
 				var panicRes any
-				renderer := compactRenderer
-				require.NoError(t, err)
 
 				func() {
 					defer func() {
@@ -118,7 +565,7 @@ func TestRenderer_RenderAllFormats(t *testing.T) {
 							panicRes = r
 						}
 					}()
-					err = renderer.Render(w, format, value)
+					err = Base.Compact(w, format, value)
 				}()
 
 				got := w.String()
@@ -152,3 +599,65 @@ func TestRenderer_RenderAllFormats(t *testing.T) {
 		}
 	}
 }
+
+func TestRenderer_PrettyAllFormats(t *testing.T) {
+	tests := []renderFormatTestCase{}
+	tests = append(tests, binaryFormattestCases...)
+	tests = append(tests, jsonFormatTestCases...)
+	tests = append(tests, textFormatTestCases...)
+	tests = append(tests, xmlFormatTestCases...)
+	tests = append(tests, yamlFormatTestCases...)
+
+	for _, tt := range tests {
+		for _, format := range tt.formats {
+			t.Run(format+" format "+tt.name, func(t *testing.T) {
+				w := &mockWriter{WriteErr: tt.writeErr}
+
+				value := tt.value
+				if tt.valueFunc != nil {
+					value = tt.valueFunc()
+				}
+
+				var err error
+				var panicRes any
+
+				func() {
+					defer func() {
+						if r := recover(); r != nil {
+							panicRes = r
+						}
+					}()
+					err = Base.Pretty(w, format, value)
+				}()
+
+				got := w.String()
+				var want string
+				if tt.wantPretty == "" && tt.wantCompact == "" {
+					want = tt.want
+				} else {
+					want = tt.wantPretty
+				}
+
+				if tt.wantPanic != "" {
+					assert.Equal(t, tt.wantPanic, panicRes)
+				}
+
+				if tt.wantErr != "" {
+					wantErr := strings.ReplaceAll(
+						tt.wantErr, "{{format}}", format,
+					)
+					assert.EqualError(t, err, wantErr)
+				}
+				for _, e := range tt.wantErrIs {
+					assert.ErrorIs(t, err, e)
+				}
+
+				if tt.wantPanic == "" &&
+					tt.wantErr == "" && len(tt.wantErrIs) == 0 {
+					assert.NoError(t, err)
+					assert.Equal(t, want, got)
+				}
+			})
+		}
+	}
+}

text.go

@@ -5,8 +5,10 @@ import (
 	"io"
 )
 
-// Text is a renderer that writes the given value to the writer as is. It
+// Text is a Handler that writes the given value to the writer as text,
-// supports rendering the following types as plain text:
+// supporting multiple types and interfaces.
+//
+// Supports rendering the following types as text:
 //
 //   - []byte
 //   - []rune
@@ -23,7 +25,10 @@ import (
 // If the value is of any other type, a ErrCannotRender error will be returned.
 type Text struct{}
 
-var _ FormatRenderer = (*Text)(nil)
+var (
+	_ Handler        = (*Text)(nil)
+	_ FormatsHandler = (*Text)(nil)
+)
 
 // Render writes the given value to the writer as text.
 func (t *Text) Render(w io.Writer, v any) error {
@@ -58,6 +63,7 @@ func (t *Text) Render(w io.Writer, v any) error {
 	return nil
 }
 
+// Formats returns a list of format strings that this Handler supports.
 func (t *Text) Formats() []string {
 	return []string{"text", "txt", "plain"}
 }

text_test.go

@@ -216,3 +216,9 @@ func TestText_Render(t *testing.T) {
 		})
 	}
 }
+
+func TestText_Formats(t *testing.T) {
+	h := &Text{}
+
+	assert.Equal(t, []string{"text", "txt", "plain"}, h.Formats())
+}

xml.go

@@ -6,35 +6,48 @@ import (
 	"io"
 )
 
+// XMLDefualtIndent is the default indentation string used by XML instances when
+// pretty rendering if no Indent value is set.
+var XMLDefualtIndent = "  "
+
 // XML is a Renderer that marshals a value to XML.
 type XML struct {
-	// Pretty specifies whether the output should be pretty-printed. If true,
+	// Prefix is the prefix added to each level of indentation when pretty
-	// the output will be indented and newlines will be added.
+	// rendering.
-	Pretty bool
-
-	// Prefix is the prefix added to each level of indentation when Pretty is
-	// true.
 	Prefix string
 
-	// Indent is the string added to each level of indentation when Pretty is
+	// Indent is the string added to each level of indentation when pretty
-	// true. If empty, two spaces will be used instead.
+	// rendering. If empty, XMLDefualtIndent be used.
 	Indent string
 }
 
-var _ FormatRenderer = (*XML)(nil)
+var (
+	_ Handler        = (*XML)(nil)
+	_ PrettyHandler  = (*XML)(nil)
+	_ FormatsHandler = (*XML)(nil)
+)
 
 // Render marshals the given value to XML.
 func (x *XML) Render(w io.Writer, v any) error {
-	enc := xml.NewEncoder(w)
+	err := xml.NewEncoder(w).Encode(v)
-	if x.Pretty {
+	if err != nil {
+		return fmt.Errorf("%w: %w", ErrFailed, err)
+	}
+
+	return nil
+}
+
+// RenderPretty marshals the given value to XML with line breaks and
+// indentation.
+func (x *XML) RenderPretty(w io.Writer, v any) error {
 	prefix := x.Prefix
 	indent := x.Indent
 	if indent == "" {
-			indent = "  "
+		indent = XMLDefualtIndent
 	}
 
+	enc := xml.NewEncoder(w)
 	enc.Indent(prefix, indent)
-	}
 
 	err := enc.Encode(v)
 	if err != nil {
@@ -44,6 +57,7 @@ func (x *XML) Render(w io.Writer, v any) error {
 	return nil
 }
 
+// Formats returns a list of format strings that this Handler supports.
 func (x *XML) Formats() []string {
 	return []string{"xml"}
 }

xml_test.go

@@ -32,7 +32,6 @@ func (mxm *mockXMLMarshaler) MarshalXML(
 func TestXML_Render(t *testing.T) {
 	tests := []struct {
 		name      string
-		pretty    bool
 		prefix    string
 		indent    string
 		value     any
@@ -41,8 +40,7 @@ func TestXML_Render(t *testing.T) {
 		wantErrIs []error
 	}{
 		{
-			name:   "simple object without pretty",
+			name: "simple object",
-			pretty: false,
 			value: struct {
 				XMLName xml.Name `xml:"user"`
 				Age     int      `xml:"age"`
@@ -50,28 +48,7 @@ func TestXML_Render(t *testing.T) {
 			want: `<user><age>30</age></user>`,
 		},
 		{
-			name:   "simple object with pretty",
+			name:   "ignores indent without pretty",
-			pretty: true,
-			value: struct {
-				XMLName xml.Name `xml:"user"`
-				Age     int      `xml:"age"`
-			}{Age: 30},
-			want: "<user>\n  <age>30</age>\n</user>",
-		},
-		{
-			name:   "pretty with prefix and indent",
-			pretty: true,
-			prefix: "//",
-			indent: "\t",
-			value: struct {
-				XMLName xml.Name `xml:"user"`
-				Age     int      `xml:"age"`
-			}{Age: 30},
-			want: "//<user>\n//\t<age>30</age>\n//</user>",
-		},
-		{
-			name:   "prefix and indent without pretty",
-			pretty: false,
 			prefix: "//",
 			indent: "\t",
 			value: struct {
@@ -93,7 +70,6 @@ func TestXML_Render(t *testing.T) {
 		},
 		{
 			name:      "invalid value",
-			pretty:    false,
 			value:     make(chan int),
 			wantErr:   "render: failed: xml: unsupported type: chan int",
 			wantErrIs: []error{Err, ErrFailed},
@@ -103,7 +79,6 @@ func TestXML_Render(t *testing.T) {
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
 			x := &XML{
-				Pretty: tt.pretty,
 				Prefix: tt.prefix,
 				Indent: tt.indent,
 			}
@@ -126,3 +101,82 @@ func TestXML_Render(t *testing.T) {
 		})
 	}
 }
+
+func TestXML_RenderPretty(t *testing.T) {
+	tests := []struct {
+		name      string
+		prefix    string
+		indent    string
+		value     any
+		want      string
+		wantErr   string
+		wantErrIs []error
+	}{
+		{
+			name: "simple object",
+			value: struct {
+				XMLName xml.Name `xml:"user"`
+				Age     int      `xml:"age"`
+			}{Age: 30},
+			want: "<user>\n  <age>30</age>\n</user>",
+		},
+		{
+			name:   "uses prefix and indent",
+			prefix: "//",
+			indent: "\t",
+			value: struct {
+				XMLName xml.Name `xml:"user"`
+				Age     int      `xml:"age"`
+			}{Age: 30},
+			want: "//<user>\n//\t<age>30</age>\n//</user>",
+		},
+		{
+			name:  "implements xml.Marshaler",
+			value: &mockXMLMarshaler{elm: "test string"},
+			want:  "<mockXMLMarshaler>test string</mockXMLMarshaler>",
+		},
+		{
+			name:      "error from xml.Marshaler",
+			value:     &mockXMLMarshaler{err: errors.New("mock error")},
+			wantErr:   "render: failed: mock error",
+			wantErrIs: []error{Err, ErrFailed},
+		},
+		{
+			name:      "invalid value",
+			value:     make(chan int),
+			wantErr:   "render: failed: xml: unsupported type: chan int",
+			wantErrIs: []error{Err, ErrFailed},
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			x := &XML{
+				Prefix: tt.prefix,
+				Indent: tt.indent,
+			}
+			var buf bytes.Buffer
+
+			err := x.RenderPretty(&buf, tt.value)
+			got := buf.String()
+
+			if tt.wantErr != "" {
+				assert.EqualError(t, err, tt.wantErr)
+			}
+			for _, e := range tt.wantErrIs {
+				assert.ErrorIs(t, err, e)
+			}
+
+			if tt.wantErr == "" && len(tt.wantErrIs) == 0 {
+				assert.NoError(t, err)
+				assert.Equal(t, tt.want, got)
+			}
+		})
+	}
+}
+
+func TestXML_Formats(t *testing.T) {
+	h := &XML{}
+
+	assert.Equal(t, []string{"xml"}, h.Formats())
+}

yaml.go

@@ -7,24 +7,28 @@ import (
 	"gopkg.in/yaml.v3"
 )
 
-// YAML is a renderer that marshals the given value to YAML.
+var YAMLDefaultIndent = 2
+
+// YAML is a Handler that marshals the given value to YAML.
 type YAML struct {
 	// Indent controls how many spaces will be used for indenting nested blocks
-	// in the output YAML. When Indent is zero, 2 will be used by default.
+	// in the output YAML. When Indent is zero, YAMLDefaultIndent will be used.
 	Indent int
 }
 
-var _ FormatRenderer = (*YAML)(nil)
+var (
+	_ Handler        = (*YAML)(nil)
+	_ FormatsHandler = (*YAML)(nil)
+)
 
 // Render marshals the given value to YAML.
 func (y *YAML) Render(w io.Writer, v any) error {
-	enc := yaml.NewEncoder(w)
-
 	indent := y.Indent
 	if indent == 0 {
-		indent = 2
+		indent = YAMLDefaultIndent
 	}
 
+	enc := yaml.NewEncoder(w)
 	enc.SetIndent(indent)
 
 	err := enc.Encode(v)
@@ -35,6 +39,7 @@ func (y *YAML) Render(w io.Writer, v any) error {
 	return nil
 }
 
+// Formats returns a list of format strings that this Handler supports.
 func (y *YAML) Formats() []string {
 	return []string{"yaml", "yml"}
 }

yaml_test.go

@@ -24,7 +24,7 @@ func TestYAML_Render(t *testing.T) {
 	tests := []struct {
 		name      string
 		indent    int
-		value     interface{}
+		value     any
 		want      string
 		wantErr   string
 		wantErrIs []error
@@ -113,3 +113,9 @@ func TestYAML_Render(t *testing.T) {
 		})
 	}
 }
+
+func TestYAML_Formats(t *testing.T) {
+	h := &YAML{}
+
+	assert.Equal(t, []string{"yaml", "yml"}, h.Formats())
+}