Add "func" Decoder

decode_test.go

@@ -152,6 +152,7 @@ func Test_Decoder(t *testing.T) {
 			B string `json:"str"`
 			C bool
 			D *T
+			E func()
 		}
 		content := []byte(`
 {
@@ -162,7 +163,8 @@ func Test_Decoder(t *testing.T) {
     "aa": 2,
     "bb": "world",
     "cc": true
-  }
+  },
+  "e"   : null
 }`)
 		assertErr(t, json.Unmarshal(content, &v))
 		assertEq(t, "struct.A", 123, v.A)
@@ -171,6 +173,7 @@ func Test_Decoder(t *testing.T) {
 		assertEq(t, "struct.D.AA", 2, v.D.AA)
 		assertEq(t, "struct.D.BB", "world", v.D.BB)
 		assertEq(t, "struct.D.CC", true, v.D.CC)
+		assertEq(t, "struct.E", nil, v.E)
 		t.Run("struct.field null", func(t *testing.T) {
 			var v struct {
 				A string
@@ -179,8 +182,9 @@ func Test_Decoder(t *testing.T) {
 				D map[string]interface{}
 				E [2]string
 				F interface{}
+				G func()
 			}
-			assertErr(t, json.Unmarshal([]byte(`{"a":null,"b":null,"c":null,"d":null,"e":null,"f":null}`), &v))
+			assertErr(t, json.Unmarshal([]byte(`{"a":null,"b":null,"c":null,"d":null,"e":null,"f":null,"g":null}`), &v))
 			assertEq(t, "string", v.A, "")
 			assertNeq(t, "[]string", v.B, nil)
 			assertEq(t, "[]string", len(v.B), 0)
@@ -191,6 +195,7 @@ func Test_Decoder(t *testing.T) {
 			assertNeq(t, "array", v.E, nil)
 			assertEq(t, "array", len(v.E), 2)
 			assertEq(t, "interface{}", v.F, nil)
+			assertEq(t, "func", v.G, nil)
 		})
 	})
 	t.Run("interface", func(t *testing.T) {
@@ -239,6 +244,11 @@ func Test_Decoder(t *testing.T) {
 			assertEq(t, "interface", nil, v)
 		})
 	})
+	t.Run("func", func(t *testing.T) {
+		var v func()
+		assertErr(t, json.Unmarshal([]byte(`null`), &v))
+		assertEq(t, "func", nil, v)
+	})
 }
 
 func TestIssue98(t *testing.T) {

helper_test.go

@@ -11,7 +11,7 @@ func assertErr(t *testing.T, err error) {
 
 func assertEq(t *testing.T, msg string, exp interface{}, act interface{}) {
 	t.Helper()
-	if exp != act {
+	if exp != act && exp != nil && act != nil {
 		t.Fatalf("failed to test for %s. exp=[%v] but act=[%v]", msg, exp, act)
 	}
 }

internal/decoder/compile.go

@@ -123,11 +123,15 @@ func compile(typ *runtime.Type, structName, fieldName string, structTypeToDecode
 		return compileFloat32(structName, fieldName)
 	case reflect.Float64:
 		return compileFloat64(structName, fieldName)
+	case reflect.Func:
+		return compileFunc(typ, structName, fieldName)
 	}
 	return nil, &errors.UnmarshalTypeError{
 		Value:  "object",
 		Type:   runtime.RType2Type(typ),
 		Offset: 0,
+		Struct: structName,
+		Field:  fieldName,
 	}
 }
 
@@ -178,6 +182,8 @@ ERROR:
 		Value:  "object",
 		Type:   runtime.RType2Type(typ),
 		Offset: 0,
+		Struct: structName,
+		Field:  fieldName,
 	}
 }
 
@@ -312,6 +318,10 @@ func compileInterface(typ *runtime.Type, structName, fieldName string) (Decoder,
 	return newInterfaceDecoder(typ, structName, fieldName), nil
 }
 
+func compileFunc(typ *runtime.Type, strutName, fieldName string) (Decoder, error) {
+	return newFuncDecoder(typ, strutName, fieldName), nil
+}
+
 func removeConflictFields(fieldMap map[string]*structFieldSet, conflictedMap map[string]struct{}, dec *structDecoder, field reflect.StructField) {
 	for k, v := range dec.fieldMap {
 		if _, exists := conflictedMap[k]; exists {

internal/decoder/func.go

@@ -0,0 +1,108 @@
+package decoder
+
+import (
+	"bytes"
+	"unsafe"
+
+	"github.com/goccy/go-json/internal/errors"
+	"github.com/goccy/go-json/internal/runtime"
+)
+
+type funcDecoder struct {
+	typ        *runtime.Type
+	structName string
+	fieldName  string
+}
+
+func newFuncDecoder(typ *runtime.Type, structName, fieldName string) *funcDecoder {
+	fnDecoder := &funcDecoder{typ, structName, fieldName}
+	return fnDecoder
+}
+
+func (d *funcDecoder) DecodeStream(s *Stream, depth int64, p unsafe.Pointer) error {
+	s.skipWhiteSpace()
+	start := s.cursor
+	if err := s.skipValue(depth); err != nil {
+		return err
+	}
+	src := s.buf[start:s.cursor]
+	if len(src) > 0 {
+		switch src[0] {
+		case '"':
+			return &errors.UnmarshalTypeError{
+				Value:  "string",
+				Type:   runtime.RType2Type(d.typ),
+				Offset: s.totalOffset(),
+			}
+		case '[':
+			return &errors.UnmarshalTypeError{
+				Value:  "array",
+				Type:   runtime.RType2Type(d.typ),
+				Offset: s.totalOffset(),
+			}
+		case '{':
+			return &errors.UnmarshalTypeError{
+				Value:  "object",
+				Type:   runtime.RType2Type(d.typ),
+				Offset: s.totalOffset(),
+			}
+		case '-', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9':
+			return &errors.UnmarshalTypeError{
+				Value:  "number",
+				Type:   runtime.RType2Type(d.typ),
+				Offset: s.totalOffset(),
+			}
+		case 'n':
+			if bytes.Equal(src, nullbytes) {
+				*(*unsafe.Pointer)(p) = nil
+				return nil
+			}
+		}
+	}
+	return errors.ErrNotAtBeginningOfValue(start)
+}
+
+func (d *funcDecoder) Decode(ctx *RuntimeContext, cursor, depth int64, p unsafe.Pointer) (int64, error) {
+	buf := ctx.Buf
+	cursor = skipWhiteSpace(buf, cursor)
+	start := cursor
+	end, err := skipValue(buf, cursor, depth)
+	if err != nil {
+		return 0, err
+	}
+	src := buf[start:end]
+	if len(src) > 0 {
+		switch src[0] {
+		case '"':
+			return 0, &errors.UnmarshalTypeError{
+				Value:  "string",
+				Type:   runtime.RType2Type(d.typ),
+				Offset: start,
+			}
+		case '[':
+			return 0, &errors.UnmarshalTypeError{
+				Value:  "array",
+				Type:   runtime.RType2Type(d.typ),
+				Offset: start,
+			}
+		case '{':
+			return 0, &errors.UnmarshalTypeError{
+				Value:  "object",
+				Type:   runtime.RType2Type(d.typ),
+				Offset: start,
+			}
+		case '-', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9':
+			return 0, &errors.UnmarshalTypeError{
+				Value:  "number",
+				Type:   runtime.RType2Type(d.typ),
+				Offset: start,
+			}
+		case 'n':
+			if bytes.Equal(src, nullbytes) {
+				*(*unsafe.Pointer)(p) = nil
+				return end, nil
+			}
+		}
+	}
+	return 0, errors.ErrNotAtBeginningOfValue(start)
+}