Correct way to initialize empty slice

arrays go slice
eouti picture eouti · Mar 20, 2015 · Viewed 228.3k times · Source

To declare an empty slice, with a non-fixed size, is it better to do:

mySlice1 := make([]int, 0)

or:

mySlice2 := []int{}

Just wondering which one is the correct way.

Answer

ANisus picture ANisus · Mar 20, 2015

The two alternative you gave are semantically identical, but using make([]int, 0) will result in an internal call to runtime.makeslice (Go 1.14).

You also have the option to leave it with a nil value:

var myslice []int

As written in the Golang.org blog:

a nil slice is functionally equivalent to a zero-length slice, even though it points to nothing. It has length zero and can be appended to, with allocation.

A nil slice will however json.Marshal() into "null" whereas an empty slice will marshal into "[]", as pointed out by @farwayer.

None of the above options will cause any allocation, as pointed out by @ArmanOrdookhani.

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