Add generics to chan and callback-using functions

.github/workflows/go.yml

@@ -16,7 +16,7 @@ jobs:
     - name: Set up Go 1.x
       uses: actions/setup-go@v2
       with:
-        go-version: ^1.11
+        go-version: ^1.18
 
     - name: Check out code into the Go module directory
       uses: actions/checkout@v2

csv.go

@@ -162,12 +162,12 @@ func MarshalWithoutHeaders(in interface{}, out io.Writer) (err error) {
 }
 
 // MarshalChan returns the CSV read from the channel.
-func MarshalChan(c <-chan interface{}, out CSVWriter) error {
+func MarshalChan[T any](c <-chan T, out CSVWriter) error {
 	return writeFromChan(out, c, false)
 }
 
 // MarshalChanWithoutHeaders returns the CSV read from the channel.
-func MarshalChanWithoutHeaders(c <-chan interface{}, out CSVWriter) error {
+func MarshalChanWithoutHeaders[T any](c <-chan T, out CSVWriter) error {
 	return writeFromChan(out, c, true)
 }
 
@@ -278,24 +278,23 @@ func UnmarshalCSVToMap(in CSVReader, out interface{}) error {
 
 // UnmarshalToChan parses the CSV from the reader and send each value in the chan c.
 // The channel must have a concrete type.
-func UnmarshalToChan(in io.Reader, c interface{}) error {
+func UnmarshalToChan[T any](in io.Reader, c chan<- T) error {
 	if c == nil {
 		return fmt.Errorf("goscv: channel is %v", c)
 	}
 	return readEach(newSimpleDecoderFromReader(in), nil, c)
 }
 
-// UnmarshalToChanWithErrorHandler parses the CSV from the reader in the interface.
-func UnmarshalToChanWithErrorHandler(in io.Reader, errorHandler ErrorHandler, c interface{}) error {
+// UnmarshalToChanWithErrorHandler parses the CSV from the reader in the channel.
+func UnmarshalToChanWithErrorHandler[T any](in io.Reader, errorHandler ErrorHandler, c chan<- T) error {
 	if c == nil {
 		return fmt.Errorf("goscv: channel is %v", c)
 	}
 	return readEach(newSimpleDecoderFromReader(in), errorHandler, c)
 }
 
 // UnmarshalToChanWithoutHeaders parses the CSV from the reader and send each value in the chan c.
-// The channel must have a concrete type.
-func UnmarshalToChanWithoutHeaders(in io.Reader, c interface{}) error {
+func UnmarshalToChanWithoutHeaders[T any](in io.Reader, c chan<- T) error {
 	if c == nil {
 		return fmt.Errorf("goscv: channel is %v", c)
 	}
@@ -304,125 +303,99 @@ func UnmarshalToChanWithoutHeaders(in io.Reader, c interface{}) error {
 
 // UnmarshalDecoderToChan parses the CSV from the decoder and send each value in the chan c.
 // The channel must have a concrete type.
-func UnmarshalDecoderToChan(in SimpleDecoder, c interface{}) error {
+func UnmarshalDecoderToChan[T any](in SimpleDecoder, c chan<- T) error {
 	if c == nil {
 		return fmt.Errorf("goscv: channel is %v", c)
 	}
 	return readEach(in, nil, c)
 }
 
-// UnmarshalStringToChan parses the CSV from the string and send each value in the chan c.
-// The channel must have a concrete type.
-func UnmarshalStringToChan(in string, c interface{}) error {
+// UnmarshalStringToChan parses the CSV from the string and send each value in
+// the chan c.
+func UnmarshalStringToChan[T any](in string, c chan<- T) error {
 	return UnmarshalToChan(strings.NewReader(in), c)
 }
 
-// UnmarshalBytesToChan parses the CSV from the bytes and send each value in the chan c.
-// The channel must have a concrete type.
-func UnmarshalBytesToChan(in []byte, c interface{}) error {
+// UnmarshalBytesToChan parses the CSV from the bytes and send each value in the
+// chan c.
+func UnmarshalBytesToChan[T any](in []byte, c chan<- T) error {
 	return UnmarshalToChan(bytes.NewReader(in), c)
 }
 
-// UnmarshalToCallback parses the CSV from the reader and send each value to the given func f.
-// The func must look like func(Struct).
-func UnmarshalToCallback(in io.Reader, f interface{}) error {
-	valueFunc := reflect.ValueOf(f)
-	t := reflect.TypeOf(f)
-	if t.NumIn() != 1 {
-		return fmt.Errorf("the given function must have exactly one parameter")
-	}
+// UnmarshalToCallback parses the CSV from the reader and send each value to the
+// given func callback.
+func UnmarshalToCallback[T any](in io.Reader, callback func(T) error) error {
 	cerr := make(chan error)
-	c := reflect.MakeChan(reflect.ChanOf(reflect.BothDir, t.In(0)), 0)
+	c := make(chan T)
 	go func() {
-		cerr <- UnmarshalToChan(in, c.Interface())
+		cerr <- UnmarshalToChan(in, c)
 	}()
 	for {
 		select {
 		case err := <-cerr:
 			return err
 		default:
 		}
-		v, notClosed := c.Recv()
-		if !notClosed || v.Interface() == nil {
+		v, notClosed := <-c
+		if !notClosed {
 			break
 		}
-		callResults := valueFunc.Call([]reflect.Value{v})
-		// if last returned value from Call() is an error, return it
-		if len(callResults) > 0 {
-			if err, ok := callResults[len(callResults)-1].Interface().(error); ok {
-				return err
-			}
+		err := callback(v)
+		if err != nil {
+			return err
 		}
 	}
 	return <-cerr
 }
 
-// UnmarshalDecoderToCallback parses the CSV from the decoder and send each value to the given func f.
-// The func must look like func(Struct).
-func UnmarshalDecoderToCallback(in SimpleDecoder, f interface{}) error {
-	valueFunc := reflect.ValueOf(f)
-	t := reflect.TypeOf(f)
-	if t.NumIn() != 1 {
-		return fmt.Errorf("the given function must have exactly one parameter")
-	}
+// UnmarshalDecoderToCallback parses the CSV from the decoder and send each value to the given func callback.
+func UnmarshalDecoderToCallback[T any](in SimpleDecoder, callback func(T) error) error {
 	cerr := make(chan error)
-	c := reflect.MakeChan(reflect.ChanOf(reflect.BothDir, t.In(0)), 0)
+	c := make(chan T)
 	go func() {
-		cerr <- UnmarshalDecoderToChan(in, c.Interface())
+		cerr <- UnmarshalDecoderToChan(in, c)
 	}()
 	for {
 		select {
 		case err := <-cerr:
 			return err
 		default:
 		}
-		v, notClosed := c.Recv()
-		if !notClosed || v.Interface() == nil {
+		v, notClosed := <-c
+		if !notClosed {
 			break
 		}
-		valueFunc.Call([]reflect.Value{v})
+		err := callback(v)
+		if err != nil {
+			return err
+		}
 	}
 	return <-cerr
 }
 
-// UnmarshalBytesToCallback parses the CSV from the bytes and send each value to the given func f.
-// The func must look like func(Struct).
-func UnmarshalBytesToCallback(in []byte, f interface{}) error {
-	return UnmarshalToCallback(bytes.NewReader(in), f)
+// UnmarshalBytesToCallback parses the CSV from the bytes and send each value to
+// the given func callback.
+func UnmarshalBytesToCallback[T any](in []byte, callback func(T) error) error {
+	return UnmarshalToCallback(bytes.NewReader(in), callback)
 }
 
-// UnmarshalStringToCallback parses the CSV from the string and send each value to the given func f.
-// The func must look like func(Struct).
-func UnmarshalStringToCallback(in string, c interface{}) (err error) {
-	return UnmarshalToCallback(strings.NewReader(in), c)
+// UnmarshalStringToCallback parses the CSV from the string and send each value
+// to the given func callback.
+func UnmarshalStringToCallback[T any](in string, callback func(T) error) error {
+	return UnmarshalToCallback(strings.NewReader(in), callback)
 }
 
 // UnmarshalToCallbackWithError parses the CSV from the reader and
-// send each value to the given func f.
+// send each value to the given func callback.
 //
 // If func returns error, it will stop processing, drain the
 // parser and propagate the error to caller.
-//
-// The func must look like func(Struct) error.
-func UnmarshalToCallbackWithError(in io.Reader, f interface{}) error {
-	valueFunc := reflect.ValueOf(f)
-	t := reflect.TypeOf(f)
-	if t.NumIn() != 1 {
-		return fmt.Errorf("the given function must have exactly one parameter")
-	}
-	if t.NumOut() != 1 {
-		return fmt.Errorf("the given function must have exactly one return value")
-	}
-	if !isErrorType(t.Out(0)) {
-		return fmt.Errorf("the given function must only return error")
-	}
-
+func UnmarshalToCallbackWithError[T any](in io.Reader, callback func(T) error) error {
 	cerr := make(chan error)
-	c := reflect.MakeChan(reflect.ChanOf(reflect.BothDir, t.In(0)), 0)
+	c := make(chan T)
 	go func() {
-		cerr <- UnmarshalToChan(in, c.Interface())
+		cerr <- UnmarshalToChan(in, c)
 	}()
-
 	var fErr error
 	for {
 		select {
@@ -433,39 +406,37 @@ func UnmarshalToCallbackWithError(in io.Reader, f interface{}) error {
 			return fErr
 		default:
 		}
-		v, notClosed := c.Recv()
-		if !notClosed || v.Interface() == nil {
+		v, notClosed := <-c
+		if !notClosed {
 			if err := <-cerr; err != nil {
 				fErr = err
 			}
 			break
 		}
 
-		// callback f has already returned an error, stop processing but keep draining the chan c
+		// callback has already returned an error, stop processing but keep draining the chan c
 		if fErr != nil {
 			continue
 		}
 
-		results := valueFunc.Call([]reflect.Value{v})
-
-		// If the callback f returns an error, stores it and returns it in future.
-		errValue := results[0].Interface()
-		if errValue != nil {
-			fErr = errValue.(error)
+		// If the callback returns an error, stores it and returns it in future.
+		err := callback(v)
+		if err != nil {
+			fErr = err
 		}
 	}
 	return fErr
 }
 
 // UnmarshalBytesToCallbackWithError parses the CSV from the bytes and
-// send each value to the given func f.
+// send each value to the given func callback.
 //
 // If func returns error, it will stop processing, drain the
 // parser and propagate the error to caller.
 //
 // The func must look like func(Struct) error.
-func UnmarshalBytesToCallbackWithError(in []byte, f interface{}) error {
-	return UnmarshalToCallbackWithError(bytes.NewReader(in), f)
+func UnmarshalBytesToCallbackWithError[T any](in []byte, callback func(T) error) error {
+	return UnmarshalToCallbackWithError(bytes.NewReader(in), callback)
 }
 
 // UnmarshalStringToCallbackWithError parses the CSV from the string and
@@ -475,8 +446,8 @@ func UnmarshalBytesToCallbackWithError(in []byte, f interface{}) error {
 // parser and propagate the error to caller.
 //
 // The func must look like func(Struct) error.
-func UnmarshalStringToCallbackWithError(in string, c interface{}) (err error) {
-	return UnmarshalToCallbackWithError(strings.NewReader(in), c)
+func UnmarshalStringToCallbackWithError[T any](in string, callback func(T) error) error {
+	return UnmarshalToCallbackWithError(strings.NewReader(in), callback)
 }
 
 // CSVToMap creates a simple map from a CSV of 2 columns.

csv_test.go

@@ -7,14 +7,14 @@ import (
 
 func TestUnmarshalToCallback_ReaderError(t *testing.T) {
 	type Dummy struct{}
-	var reader = &errorReader{}
+	reader := &errorReader{}
 
-	err := UnmarshalToCallback(reader, func(Dummy) {})
+	err := UnmarshalToCallback(reader, func(Dummy) error { return nil })
 	if !errors.Is(err, readerErr) {
 		t.Error("UnmarshalToCallback should return first reader error")
 	}
 
-	err = UnmarshalDecoderToCallback(newSimpleDecoderFromReader(reader), func(Dummy) {})
+	err = UnmarshalDecoderToCallback(newSimpleDecoderFromReader(reader), func(Dummy) error { return nil })
 	if !errors.Is(err, readerErr) {
 		t.Error("UnmarshalDecoderToCallback should return first reader error")
 	}

decode_test.go

@@ -616,8 +616,9 @@ func TestUnmarshalToCallback(t *testing.T) {
 aa,bb,11,cc,dd,ee
 ff,gg,22,hh,ii,jj`)
 	var samples []SkipFieldSample
-	if err := UnmarshalBytesToCallback(b.Bytes(), func(s SkipFieldSample) {
+	if err := UnmarshalBytesToCallback(b.Bytes(), func(s SkipFieldSample) error {
 		samples = append(samples, s)
+		return nil
 	}); err != nil {
 		t.Fatal(err)
 	}
@@ -1020,8 +1021,9 @@ f,1,baz,,        *string
 e,3,b,,                            `)
 
 	var samples []Sample
-	if err := UnmarshalDecoderToCallback(&trimDecoder{LazyCSVReader(b)}, func(s Sample) {
+	if err := UnmarshalDecoderToCallback(&trimDecoder{LazyCSVReader(b)}, func(s Sample) error {
 		samples = append(samples, s)
+		return nil
 	}); err != nil {
 		t.Fatal(err)
 	}

encode.go

@@ -7,9 +7,7 @@ import (
 	"reflect"
 )
 
-var (
-	ErrChannelIsClosed = errors.New("channel is closed")
-)
+var ErrChannelIsClosed = errors.New("channel is closed")
 
 type encoder struct {
 	out io.Writer
@@ -19,7 +17,7 @@ func newEncoder(out io.Writer) *encoder {
 	return &encoder{out}
 }
 
-func writeFromChan(writer CSVWriter, c <-chan interface{}, omitHeaders bool) error {
+func writeFromChan[T any](writer CSVWriter, c <-chan T, omitHeaders bool) error {
 	// Get the first value. It wil determine the header structure.
 	firstValue, ok := <-c
 	if !ok {

go.mod

@@ -1,3 +1,3 @@
 module github.com/gocarina/gocsv
 
-go 1.13
+go 1.18