How to test for an empty seq in Nim?

Question

Let's say I have the following sequences:

var s1: seq[int] = @[]
var s2: seq[int]
var s3: seq[int] = nil
var s4: seq[int] = newSeq[int](4)

Which of these are typically considered "empty"? And what is the most idiomatic way to test if they are empty?

Right now I am just checking if len is 0:

proc doSomething(s: seq[int]) =
  if s.len() == 0:
    echo("Your sequence is empty.")
  else:
    # do something

I think `s.len == 0` is pretty idiomatic. Note that it will work for `nil` seqs and empty seqs. You can also check for `nil` explicitly with `s.isNil`. — uran, Feb 07 '18 at 09:41
The empty ones are empty, so of course that's s1, s2, and s4, but not s3, because that doesn't even compile any more. — Jim Balter, Jun 15 '20 at 07:25

score 6 · Accepted Answer · answered Feb 07 '18 at 20:33

6

The strutils module provides an isNullOrEmpty proc for strings: https://nim-lang.org/docs/strutils.html#isNilOrEmpty,string

As you can see in its implementation it just checks for len(s) == 0.

answered Feb 07 '18 at 20:33

def-

2

There's no longer any such proc because sequences can no longer be nil. – Jim Balter Jun 15 '20 at 07:25

score 1 · Answer 2 · answered Feb 27 '23 at 23:53

1

As of now, sequences cannot be nil, so checking for length is sufficient.

For strings specifically, we also have isEmptyOrWhitespace if you also want to consider whitespace strings.

answered Feb 27 '23 at 23:53

éclairevoyant

2 Answers2