func support json serialize

cast_test.go

@@ -7,6 +7,7 @@ package cast
 
 import (
 	"errors"
+	"encoding/json"
 	"fmt"
 	"html/template"
 	"testing"
@@ -599,6 +600,19 @@ func TestToStringE(t *testing.T) {
 	}
 	key := &Key{"foo"}
 
+	type Stru struct {
+		K string
+	}
+	stru := &Stru{K:"foo"}
+
+	struStr, _ := json.Marshal(stru)
+
+	dic := map[string]interface{}{
+		"obj": map[string]int{"key": 123},
+	}
+
+	dicStr, _ := json.Marshal(dic)
+
 	tests := []struct {
 		input  interface{}
 		expect string
@@ -620,15 +634,19 @@ func TestToStringE(t *testing.T) {
 		{false, "false", false},
 		{nil, "", false},
 		{[]byte("one time"), "one time", false},
+		{[]byte("你好！"), "你好！", false},
+		{[]rune("你好！"), "你好！", false},
 		{"one more time", "one more time", false},
 		{template.HTML("one time"), "one time", false},
 		{template.URL("http://somehost.foo"), "http://somehost.foo", false},
 		{template.JS("(1+2)"), "(1+2)", false},
 		{template.CSS("a"), "a", false},
 		{template.HTMLAttr("a"), "a", false},
+		{dic, string(dicStr), false},
+		{stru, string(struStr), false},
 		// errors
-		{testing.T{}, "", true},
+		{testing.T{}, "{}", false},
-		{key, "", true},
+		{key, "{}", false},
 	}
 
 	for i, test := range tests {

caste.go

@@ -830,6 +830,8 @@ func ToStringE(i interface{}) (string, error) {
 		return strconv.FormatUint(uint64(s), 10), nil
 	case []byte:
 		return string(s), nil
+	case []rune:
+		return string(s), nil
 	case template.HTML:
 		return string(s), nil
 	case template.URL:
@@ -847,6 +849,11 @@ func ToStringE(i interface{}) (string, error) {
 	case error:
 		return s.Error(), nil
 	default:
+		jsonContent, err := json.Marshal(s)
+		if err == nil {
+			return string(jsonContent), nil
+		}
+
 		return "", fmt.Errorf("unable to cast %#v of type %T to string", i, i)
 	}
 }