%v for []string{} and []string{""}

[Brian Candler]

I was slightly surprised to discover that the Print() output for an empty slice, and a 1-element slice containing the empty string, are the same:

https://play.golang.org/p/btkzgk4LMT9

It does follow logically from the rules.  I guess I need to train myself to use %q or %#v.

[tapi...@gmail.com]

Printing a nil slice also get the same output [].

I remembered Rob Pike ever said in an issue thread that this can't be changed now for compatibility reason.

[Brian Candler]

Sure.  I don't have a problem with nil slice and empty slice showing the same, because in all important ways they behave the same - i.e. they have len() of 0, you can append() to them, etc.  The only behavioural difference I can think of is if you explicitly test "foo == nil".

However, a slice with len=1 that showed the same as one with len=0, was what confused me :-)

On reflection, %v is intentionally ambiguous.  There are other examples, e.g.

- []string{"a","b"} and []string{"a b"}

- []string{"", ""} and []string{" "}

[Kevin Chowski]

The "%#v" print verb is intended to be used for unambiguous printing of a type, but that means it will have a prefix of `[]string` in order to ensure the type is unambiguous. I personally use %q a lot any time I know I have a string (or set of strings) which might be ambiguous in some way, but I don't want the `[]string` prefix in there. See: https://play.golang.org/p/70Ryd50IGt6