avoid data convertion during encodig

gen/decoder.go

@@ -68,8 +68,8 @@ func (g *Generator) genTypeDecoder(t reflect.Type, out string, tags fieldTags, i
 
 	unmarshalerIface = reflect.TypeOf((*encoding.TextUnmarshaler)(nil)).Elem()
 	if reflect.PtrTo(t).Implements(unmarshalerIface) {
-		fmt.Fprintln(g.out, ws+"if data := in.UnsafeString(); in.Ok() {")
-		fmt.Fprintln(g.out, ws+"  in.AddError( ("+out+").UnmarshalText([]byte(data)) )")
+		fmt.Fprintln(g.out, ws+"if data := in.UnsafeBytes(); in.Ok() {")
+		fmt.Fprintln(g.out, ws+"  in.AddError( ("+out+").UnmarshalText(data) )")
 		fmt.Fprintln(g.out, ws+"}")
 		return nil
 	}

jlexer/lexer.go

@@ -618,6 +618,12 @@ func (r *Lexer) UnsafeString() string {
 	return ret
 }
 
+// UnsafeBytes returns the byte slice if the token is a string literal.
+func (r *Lexer) UnsafeBytes() []byte {
+	_, ret := r.unsafeString()
+	return ret
+}
+
 // String reads a string literal.
 func (r *Lexer) String() string {
 	if r.token.kind == tokenUndef && r.Ok() {