Correct way to initialize empty slice

Question

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 1

The two alternative you gave are semantically identical, but using make([]int, 0) will result in an internal call to runtime.makeslice (Go 1.16).

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.

Answer 2

They are equivalent. See this code:

mySlice1 := make([]int, 0) mySlice2 := []int{} fmt.Println("mySlice1", cap(mySlice1)) fmt.Println("mySlice2", cap(mySlice2)) 

Output:

mySlice1 0 mySlice2 0 

Both slices have 0 capacity which implies both slices have 0 length (cannot be greater than the capacity) which implies both slices have no elements. This means the 2 slices are identical in every aspect.

See similar questions:

What is the point of having nil slice and empty slice in golang?

nil slices vs non-nil slices vs empty slices in Go language