[swift-evolution] [Review] SE-0023 API Design Guidelines

[Brent Royal-Gordon]

> Also, an exclamation mark (!) is generally used to indicate that a function/method mutates `self`:

It's a common misconception that `!` means "mutates" in Ruby. It actually means something like "more dangerous variant". The danger being indicated is *often* that it mutates, but sometimes it's that it throws an exception (rather than returning `false` or `nil`) or bypasses validations. There is also a rule in Ruby that you should never use `!` unless there's a non-`!` variant.

-- 
Brent Royal-Gordon
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