add func decoder

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)
+}