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reflect.NewAt() Function in Golang with Examples

  • Last Updated : 03 May, 2020

Go language provides inbuilt support implementation of run-time reflection and allowing a program to manipulate objects with arbitrary types with the help of reflect package. The reflect.NewAt() Function in Golang is used to get the Value representing a pointer to a value of the specified type, using p as that pointer. To access this function, one needs to imports the reflect package in the program.

Syntax:

func NewAt(typ Type, p unsafe.Pointer) Value

Parameters: This function takes the following parameters:

  • typ : This parameter is the Type.
  • p : This parameter is the unsafe.Pointer.

Return Value: This function returns a Value representing a pointer to a value of the specified type.

Below examples illustrate the use of the above method in Golang:



Example 1:




// Golang program to illustrate
// reflect.NewAt() Function 
  
package main
  
import (
    "reflect"
    "unsafe"
    "fmt"
)
  
func main() {
    var s = struct{ foo int }{100}
    var i int
  
    rs := reflect.ValueOf(&s).Elem() 
    rf := rs.Field(0)              
    ri := reflect.ValueOf(&i).Elem()
      
    // use of NewAt() method
    rf = reflect.NewAt(rf.Type(), unsafe.Pointer(rf.UnsafeAddr())).Elem()
    ri.Set(rf)
    rf.Set(ri)
      
    fmt.Println(rf)
}

Output:

100

Example 2:




// Golang program to illustrate
// reflect.NewAt() Function 
  
package main
  
import (
    "fmt"
    "play.ground/foo"
    "reflect"
    "unsafe"
)
  
func GetUnexportedField(field reflect.Value) interface{} {
    return reflect.NewAt(field.Type(), 
      unsafe.Pointer(field.UnsafeAddr())).Elem().Interface()
}
  
func SetUnexportedField(field reflect.Value, value interface{}) {
    reflect.NewAt(field.Type(), unsafe.Pointer(field.UnsafeAddr())).
        Elem().
        Set(reflect.ValueOf(value))
}
  
func main() {
    f := &foo.Foo{
        Exported: "Old Value ",
    }
  
    fmt.Println(f.Exported) 
      
    field := reflect.ValueOf(f).Elem().FieldByName("unexported")
    SetUnexportedField(field, "New Value")
    fmt.Println(GetUnexportedField(field))
}
  
-- go.mod --
module play.ground
  
-- foo/foo.go --
package foo
  
type Foo struct {
    Exported   string
    unexported string
}

Output:

Old Value 
New Value



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