reflect.CanSet() 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.CanSet() Function in Golang is used to check whether the value of v can be changed. To access this function, one needs to imports the reflect package in the program.

Syntax:
func (v Value) CanSet() bool
Parameters: This function does not accept any parameters.
Return Value: This function returns the boolean value.

Below examples illustrate the use of above method in Golang:

Example 1:

// Golang program to illustrate
// reflect.CanSet() Function
  
package main
  
import (
    "reflect"
    "fmt"
  
)
  
type ProductionInfo struct {
    StructA []Entry
}
  
type Entry struct {
    Field1            string
    Field2            int
}
  
func SetField(source interface{}, fieldName string, fieldValue string){
    v := reflect.ValueOf(source)
    tt := reflect.TypeOf(source)
      
    for k := 0; k < tt.NumField(); k++ {
        fieldValue := reflect.ValueOf(v.Field(k))
          
        // use of CanSet() method
        fmt.Println(fieldValue.CanSet())
        if fieldValue.CanSet(){
            fieldValue.SetString(fieldValue.String())
        }
    }
}
  
// Main function
func main() {
    source := ProductionInfo{}
    source.StructA = append(source.StructA, Entry{Field1: "A", Field2: 2})
      
    SetField(source, "Field1", "NEW_VALUE")
}        

Output:

false

Example 2:

// Golang program to illustrate
// reflect.CanSet() Function
  
package main
  
import (
    "fmt"
    "reflect"
)
  
type ProductionInfo struct {
    StructA []Entry
}
  
type Entry struct {
    Field1 string
    Field2 int
}
  
func SetField(source interface{}, fieldName string, fieldValue string) {
    v := reflect.ValueOf(source).Elem()
      
    // use of CanSet() method
    fmt.Println(v.FieldByName(fieldName).CanSet())
  
    if v.FieldByName(fieldName).CanSet() {
        v.FieldByName(fieldName).SetString(fieldValue)
    }
}
  
// Main function
func main() {
    source := ProductionInfo{}
    source.StructA = append(source.StructA, Entry{Field1: "A", Field2: 2})
  
    fmt.Println("Before: ", source.StructA[0])
    SetField(&source.StructA[0], "Field1", "NEW_VALUE")
    fmt.Println("After: ", source.StructA[0])
}

Output:

Before:  {A 2}
true
After:  {NEW_VALUE 2}

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