reflect.CanSet() Function in Golang with Examples

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}

My Personal Notes

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