Compare string and 0

Question

I just stumbled upon this strange problem:

echo 'test' ==# 0

This returns 1. Therefore it is true. But in "reality" it is not true. Any string is different from 0. How to do this check?

For a bit more context, I actually stumbled upon it with the following code:

let l= ['one', 'two', 'three']
let value = get(l, 5)
if value ==# 0
  " do something if the list does not contain index 5
else 
  " do something with the value of the 5th list item
end

get() returns 0 if the given index is not found in the list. I need to be able to check for this case. But how to do this?

Answer 1

By design in VimScript strings can be implicitly converted to numbers. Kind of Awk-style. Use is operator instead:

:echo 'test' is 0
0

Answer 2

Matt has good advice for correcting your code. Here's some info on the first part of your question.

This is actually working as designed:

echo 'test' ==# 0

This compares 'test' to the number zero before displaying/echoing the result. In Vimscript when you compare a string to a number it gets converted to a number itself. Per :h variables (scroll down a bit) unless the string starts with a number it is converted to the number 0.

So the comparison reduces to this:

0 ==# 0

I.e. 1 (true) and that's what is displayed.

On the other hand, when a string starts with a number it gets converted to that number...

echo '3test' ==# 3

This also evaluates to and displays 1.

Yeah, it all may seem a little weird but Vimscript isn't the only language with automatic conversions like this.