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

Gans

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. – Symphonize

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. – Assiduous

Answer 1

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.

Beka

There's no longer any such proc because sequences can no longer be nil. – Assiduous

Answer 2

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.

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