The new() Function

The built-in new function allocates a zero-initialized value and returns a pointer to it.

new(int) has type *int, and the target begins as 0. You can change it with *p = 12. The expression &T{...} is often a readable alternative for struct values initialized with fields.

new does not initialize a map’s internal storage or a slice’s backing array. For those collection types, make often provides the immediately usable value you need.

Follow this diagram before executing the example. Check where a value or decision changes what runs next.

This example is a complete program. Save it as main.go or paste it into the Go Playground.

Go code

package main

import "fmt"

func main() {
	number := new(int)
	fmt.Println("Zero:", *number)
	*number = 12
	fmt.Println("Updated:", *number)
	fmt.Println("Non-nil:", number != nil)
}

Output

Zero: 0
Updated: 12
Non-nil: true

new(int) returns a non-nil pointer to a zero-valued integer. Reading yields 0; the assignment updates the allocated integer to 12.

• new(map[string]int) produces a pointer to a nil map, not an initialized writable map.
• Calling new does not necessarily force allocation on the heap; the compiler can optimize storage placement.

Use new(bool), check its zero value, and then change it through the pointer.

Tip: Edit the example above, predict the output, and run the modified code to test your reasoning.

You have practiced The new() Function in a small, self-contained program. The important habit is to predict what runs, inspect the actual output and distinguish the language rule from the particular example.

Before continuing, make sure you can explain the program to someone who has not seen it, including the line that changes its result.