Is there a difference between new() and “regular” allocation?

Question

In Go, is there a notable difference between the following two segments of code:

v := &Vector{}

as opposed to

v := new(         


        

Answer 1

According to Effective Go, new() is a function that allocates memory, and zeros it out; that is every field (and the entire piece of memory for the structure) will be set to 0s. If you design your structures so that when they're created all fields should equal zero, than it's fine and recommended to use it. If, however, you need more control over what initial values are to be used, then the more conventional method should be used.

In the specific case you mention the difference is irrelevant, but it should be noted elsewhere.

I hope this helps! :)

Answer 2

No. What they return is the same,

package main

import "fmt"
import "reflect"

type Vector struct {
    x   int
    y   int
}

func main() {
    v := &Vector{}
    x := new(Vector)
    fmt.Println(reflect.TypeOf(v))
    fmt.Println(reflect.TypeOf(x))
}

Result:

*main.Vector
*main.Vector

There is some contention on the mailing list that having both is confusing:

https://groups.google.com/forum/?fromgroups=#!topic/golang-nuts/GDXFDJgKKSs

One thing to note:

new() is the only way to get a pointer to an unnamed integer or other basic type. You can write "p := new(int)" but you can't write "p := &int{0}". Other than that, it's a matter of preference.

Source : https://groups.google.com/d/msg/golang-nuts/793ZF_yeqbk/-zyUAPT-e4IJ

Answer 3

Yes, there is a fundamental difference between the two code fragments.

v := &Vector{}

Works only for Vector being a struct type, map type, array type or a slice type

v := new(Vector)

Works for Vector of any type.

Example: http://play.golang.org/p/nAHjL1ZEuu

Answer 4

Here is a difference: for a Person struct, the JSON string marshalled from &[]*Person{} is [] and from new([]*Person) is null using json.Marshal.

Check out the sample here: https://play.golang.org/p/xKkFLoMXX1s

• https://golang.org/doc/effective_go.html#allocation_new
• https://golang.org/doc/effective_go.html#composite_literals