reflect.MakeMapWithSize() 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.MakeMapWithSize() Function in Golang is used to create a new map with the specified type and initial space for approximately n elements. To access this function, one needs to imports the reflect package in the program.

Syntax:

func MakeMapWithSize(typ Type, n int) Value

Parameters: This function takes the following parameters:

• typ : This parameter is the Type.
• n: This parameter is the number of elements.

Return Value: This function returns a newly created map.

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 map[int]string
    var n int
    n=10

    var strValue reflect.Value = reflect.ValueOf(&str)

    indirectStr := reflect.Indirect(strValue)

    //Use of MakeMapWithSize() method

    valueMap := reflect.MakeMapWithSize(indirectStr.Type(), n)

    fmt.Printf("ValueMap is [%v] .", valueMap)

}

Output:

ValueMap is [map[]] .

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)

    intSliceReflect := reflect.MakeSlice(sliceType, 0, 0)
    mapReflect := reflect.MakeMapWithSize(mapType, 100)

    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]