new() and make() functions with examples in Golang

Golang new() and make() functions: In this tutorial, we are going to learn about the two built-in functions new() and make() to allocate memory dynamically with their descriptions, syntaxes, examples.
Submitted by Anshuman Singh, on June 14, 2019 [Last updated : March 05, 2023]

In Golang, to allocate memory, we have two built-in functions new() and make().

Golang new() function

Memory returned by new() is zeroed.
new() only returns pointers to initialized memory.
new() works for all the data types (except channel, map), and dynamically allocates space for a variable of that type and initialized it to zero value of that type and return a pointer to it.

Example

    result = new(int)

is equivalent to

    var temp int   // declare an int type variable
    var result *int //  declare a pointer to int
    result = &temp

Golang code for demonstrate the example of new() function

There are three different ways to create a pointer that points to a zeroed structure value, each of which is equivalent:

package main

import "fmt"

type Sum struct {
	x_val int
	y_val int
}

func main() {
	// Allocate enough memory to store a Sum structure value
	// and return a pointer to the value's address
	var sum Sum
	p := &sum
	fmt.Println(p)

	// Use a composite literal to perform 
	//allocation and return a pointer
	// to the value's address
	p = &Sum{}
	fmt.Println(p)

	// Use the new function to perform allocation, 
	//which will return a pointer to the value's address.
	p = new(Sum)
	fmt.Println(p)
}

Output

&{0 0}
&{0 0}
&{0 0}

Golang make() function

make() only makes slices, maps, and channels. make returns value of type T(data type) not *T

Example

make([]int, 10, 20) – Here, make creates the slice, and initialize its content depending on the default data type value. here int is used, so the default value is 0.

new([20]int)[0:10] – Here, It will also create slice but returns pointers to initialized memory.

Golang code for demonstrate the example of make() function

There are two different ways to initialize a map which maps string keys to bool values are given below.

package main

import "fmt"

func main() {
	// Using make() to initialize a map.
	m := make(map[string]bool, 0)
	fmt.Println(m)

	// Using a composite literal to initialize a map.
	m = map[string]bool{}
	fmt.Println(m)
}

Output

map[]
map[]