reflect.MakeSlice() 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.MakeSlice() Function in Golang is used to create new zero-initialized slice value for the specified slice type, length, and capacity. To access this function, one needs to imports the reflect package in the program.

Syntax:
func MakeSlice(typ Type, len, cap int) Value
Parameters: This function takes the following parameters:

typ : This parameter is the Type.

len: This parameter is the number of elements.

cap: This parameter is the capacity od slice.

Return Value: This function returns a newly created slice.

Below examples illustrate the use of above method in Golang:

Example 1:

// Golang program to illustrate 
// reflect.MakeMapWithSize() Function 
     
package main 
     
import ( 
    "fmt"
    "reflect"
) 
    
// Main function 
func main() { 
       
    var str []string  
       
    var strValue reflect.Value = reflect.ValueOf(&str) 
   
    indirectStr := reflect.Indirect(strValue) 
   
    valueSlice := reflect.MakeSlice(indirectStr.Type(), 100, 1024)  
       
    kind := valueSlice.Kind() 
   
    cap := valueSlice.Cap() 
   
    length := valueSlice.Len() 
   
    fmt.Printf("Type is [%v] with capacity of %v bytes"+ 
              " and length of %v .", kind, cap, length) 
   
    
} 

Output:

Type is [slice] with capacity of 1024 bytes and length of 100 .

Example 2:

// Golang program to illustrate 
// reflect.MakeMapWithSize() Function 
    
package main 
    
import ( 
    "fmt"
    "reflect"
) 
   
// Main function 
func main() { 
       
    intSlice := make([]int, 0) 
    mapStringInt := make(map[string]int) 
   
    sliceType := reflect.TypeOf(intSlice) 
    mapType := reflect.TypeOf(mapStringInt) 
  
    //use of MakeSlice() method 
    intSliceReflect := reflect.MakeSlice(sliceType, 0, 0) 
    mapReflect := reflect.MakeMap(mapType) 
   
    v := 100 
    rv := reflect.ValueOf(v) 
    intSliceReflect = reflect.Append(intSliceReflect, rv) 
    intSlice2 := intSliceReflect.Interface().([]int) 
    fmt.Println(intSlice2) 
   
    k := "GeeksforGeeks"
    rk := reflect.ValueOf(k) 
    mapReflect.SetMapIndex(rk, rv) 
    mapStringInt2 := mapReflect.Interface().(map[string]int) 
    fmt.Println(mapStringInt2) 
   
} 

Output:

[100]
map[GeeksforGeeks:100]

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