add mapping to existing structs

Author: Ompluscator

README.md

@@ -11,6 +11,7 @@ Main features:
 * Removing existing fields from struct
 * Modifying fields' types and tags
 * Easy reading of dynamic structs
+* Mapping dynamic struct with set values to existing struct
 
 Works out-of-the-box with:
 * https://github.com/go-playground/form
@@ -210,25 +211,31 @@ import (
 "github.com/ompluscator/dynamic-struct"
 )
 
+type DataOne struct {
+Integer int `json:"int"`
+Text string `json:"someText"`
+Float float64 `json:"double"`
+}
+
+type DataTwo struct {
+Boolean bool
+Slice []int
+Anonymous string `json:"-"`
+}
+
 func main() {
-instance := dynamicstruct.NewStruct().
-AddField("Integer", 0, `json:"int"`).
-AddField("Text", "", `json:"someText"`).
-AddField("Float", 0.0, `json:"double"`).
-AddField("Boolean", false, "").
-AddField("Slice", []int{}, "").
-AddField("Anonymous", "", `json:"-"`).
+instance := dynamicstruct.MergeStructs(DataOne{}, DataTwo{}).
 Build().
 New()
 
 data := []byte(`
 {
- "int": 123,
- "someText": "example",
- "double": 123.45,
- "Boolean": true,
- "Slice": [1, 2, 3],
- "Anonymous": "avoid to read"
+"int": 123,
+"someText": "example",
+"double": 123.45,
+"Boolean": true,
+"Slice": [1, 2, 3],
+"Anonymous": "avoid to read"
 }
 `)
 
@@ -237,20 +244,30 @@ func main() {
 log.Fatal(err)
 }
 
-value := dynamicstruct.NewReader(instance)
-fmt.Println("Integer", value.GetField("Integer").Int())
-fmt.Println("Text", value.GetField("Text").String())
-fmt.Println("Float", value.GetField("Float").Float64())
-fmt.Println("Boolean", value.GetField("Boolean").Bool())
-fmt.Println("Slice", value.GetField("Slice").Interface().([]int))
-fmt.Println("Anonymous", value.GetField("Anonymous").String())
+reader := dynamicstruct.NewReader(instance)
+
+fmt.Println("Integer", reader.GetField("Integer").Int())
+fmt.Println("Text", reader.GetField("Text").String())
+fmt.Println("Float", reader.GetField("Float").Float64())
+fmt.Println("Boolean", reader.GetField("Boolean").Bool())
+fmt.Println("Slice", reader.GetField("Slice").Interface().([]int))
+fmt.Println("Anonymous", reader.GetField("Anonymous").String())
+
+var dataOne DataOne
+err = reader.ToStruct(&dataOne)
+fmt.Println(err, dataOne)
 
+var dataTwo DataTwo
+err = reader.ToStruct(&dataTwo)
+fmt.Println(err, dataTwo)
 // Out:
 // Integer 123
 // Text example
 // Float 123.45
 // Boolean true
 // Slice [1 2 3]
 // Anonymous
+// <nil> {123 example 123.45}
+// <nil> {true [1 2 3] }
 }
 ```

reader.go

@@ -1,6 +1,7 @@
 package dynamicstruct
 
 import (
+"errors"
 "fmt"
 "reflect"
 "time"
@@ -27,6 +28,8 @@ type (
 // for _, field := range reader.GetAllFields() { ...
 //
 GetAllFields() []Field
+
+ToStruct(value interface{}) error
 }
 
 // Field is a wrapper for struct's field's value.
@@ -278,6 +281,56 @@ func (r readImpl) GetAllFields() []Field {
 return fields
 }
 
+func (r readImpl) ToStruct(value interface{}) error {
+valueOf := reflect.ValueOf(value)
+
+if valueOf.Kind() != reflect.Ptr || valueOf.IsNil() {
+return errors.New("ToStruct: expected a pointer as an argument")
+}
+
+valueOf = valueOf.Elem()
+typeOf := valueOf.Type()
+
+if valueOf.Kind() != reflect.Struct {
+return errors.New("ToStruct: expected a pointer to struct as an argument")
+}
+
+for i := 0; i < valueOf.NumField(); i++ {
+fieldType := typeOf.Field(i)
+fieldValue := valueOf.Field(i)
+
+original, ok := r.fields[fieldType.Name]
+if !ok {
+continue
+}
+
+if fieldValue.CanSet() && r.haveSameTypes(original.value.Type(), fieldValue.Type()) {
+fieldValue.Set(original.value)
+}
+}
+
+return nil
+}
+
+func (r readImpl) haveSameTypes(first reflect.Type, second reflect.Type) bool {
+if first.Kind() != second.Kind() {
+return false
+}
+
+switch first.Kind() {
+case reflect.Ptr:
+return r.haveSameTypes(first.Elem(), second.Elem())
+case reflect.Struct:
+return first.PkgPath() == second.PkgPath() && first.Name() == second.Name()
+case reflect.Slice:
+return r.haveSameTypes(first.Elem(), second.Elem())
+case reflect.Map:
+return r.haveSameTypes(first.Elem(), second.Elem()) && r.haveSameTypes(first.Key(), second.Key())
+default:
+return first.Kind() == second.Kind()
+}
+}
+
 func (f fieldImpl) Name() string {
 return f.field.Name
 }