How should I define an empty slice in Go?

Question

Or more precisely, it seems like I could do any of these three things. Is there any difference between them? Which is the best and why?

1. var foo []int
2. foo := []int{}
3. foo := make([]int, 0)

Answer 1

The difference is:

1. is a nil slice (foo == nil).
2. and 3. are non-nil slices (foo != nil).

The following points are true for all three statements:

• The statement does not allocate memory.
• The slice length is zero: len(foo) == 0.
• The slice capacity is zero: cap(foo) == 0.

Playground example

Because len, cap and append work with nil slices, (1) can often be used interchangeably with (2) and (3).

All of the options are used commonly in Go code.