[swift-evolution] Location of ! in Boolean negation expressions

Darren Mo darren.mo at me.com
Sat Aug 6 02:37:17 CDT 2016

Consider code like

guard !parameters.contains(where: { !validValueRange.contains($0) }) else …

Oftentimes I need to write negation expressions like this. The location of the exclamation marks really bugs me when writing and reading this code. The natural English ordering would be something like

“Make sure parameters does not contain an element such that validValueRange does not contain this element.”

But the programming-language-imposed ordering is

“Make sure NOT parameters contains an element such that NOT validValueRange contains this element.”

See how much harder the programming language version is to understand? Most of the time I write the positive version first because it comes out so naturally, and then I add the exclamation marks afterwards. It really burdens my mind every time I need to write code like this. Let’s come up with a solution to address this!

Here’s my zero-thought solution:

guard parameters.!contains(where: { validValueRange.!contains($0) }) else …

I’d love to hear alternate solutions and whether other people are having this problem too!


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