add an option to have the default value as a list with commas as seperator

README.md

@@ -922,6 +922,53 @@ Test it with:
 $ curl -X GET "localhost:8085/testing?name=appleboy&address=xyz&birthday=1992-03-15&createTime=1562400033000000123&unixTime=1562400033"
 ```
 
+### Bind Query String or Post Data and assign default value(s)
+
+```go
+package main
+
+import (
+	"log"
+	"time"
+
+	"github.com/gin-gonic/gin"
+)
+
+type Workplace struct {
+        Employee     string    `form:"employee"`
+        Location     string    `form:"address,default=headquarter"`
+		Peripherals  []string  `form:"peripherals,multiple_default,default=monitor,mouse,keyboard`
+
+}
+
+func main() {
+	route := gin.Default()
+	route.GET("/testing", startPage)
+	route.Run(":8085")
+}
+
+func startPage(c *gin.Context) {
+	var workplace Workplace
+	// If `GET`, only `Form` binding engine (`query`) used.
+	// If `POST`, first checks the `content-type` for `JSON` or `XML`, then uses `Form` (`form-data`).
+	// See more at https://github.com/gin-gonic/gin/blob/master/binding/binding.go#L48
+	// If default value defined, and the Request does not contain the key, the default value will be used. Empty value from request overrides that behaviour
+	// If multiple_default is in front of default, the 'default' value is returned as a slice, the position of multiple_default is important
+        if c.ShouldBind(&workplace) == nil {
+                log.Println(workplace.Employee)
+                log.Println(workplace.Location)
+                log.Println(workplace.Peripherals)
+        }
+
+	c.String(200, "Success")
+}
+```
+
+Test it with:
+```sh
+$ curl -X GET "localhost:8085/testing?employee=andre"
+```
+
 ### Bind Uri
 
 See the [detail information](https://github.com/gin-gonic/gin/issues/846).

binding/form_mapping.go

@@ -142,6 +142,12 @@ func tryToSetValue(value reflect.Value, field reflect.StructField, setter setter
 	var opt string
 	for len(opts) > 0 {
 		opt, opts = head(opts, ",")
+		if k, _ := head(opt, "="); k == "multiple_default" {
+			_, values := head(opts, "=")
+			setOpt.isDefaultExists = true
+			setOpt.defaultValue = values
+			break
+		}
 
 		if k, v := head(opt, "="); k == "default" {
 			setOpt.isDefaultExists = true
@@ -161,12 +167,12 @@ func setByForm(value reflect.Value, field reflect.StructField, form map[string][
 	switch value.Kind() {
 	case reflect.Slice:
 		if !ok {
-			vs = []string{opt.defaultValue}
+			vs = strings.Split(opt.defaultValue, ",")
 		}
 		return true, setSlice(vs, value, field)
 	case reflect.Array:
 		if !ok {
-			vs = []string{opt.defaultValue}
+			vs = strings.Split(opt.defaultValue, ",")
 		}
 		if len(vs) != value.Len() {
 			return false, fmt.Errorf("%q is not valid value for %s", vs, value.Type().String())

binding/form_mapping_test.go

@@ -74,6 +74,20 @@ func TestMappingDefault(t *testing.T) {
 	assert.Equal(t, [1]int{9}, s.Array)
 }
 
+func TestMappingMultipleDefault(t *testing.T) {
+	var s struct {
+		Int   int    `form:",multiple_default,default=9"`
+		Slice []int  `form:",multiple_default,default=9"`
+		Array [1]int `form:",multiple_default,default=9"`
+	}
+	err := mappingByPtr(&s, formSource{}, "form")
+	assert.NoError(t, err)
+
+	assert.Equal(t, 9, s.Int)
+	assert.Equal(t, []int{9}, s.Slice)
+	assert.Equal(t, [1]int{9}, s.Array)
+}
+
 func TestMappingSkipField(t *testing.T) {
 	var s struct {
 		A int