[swift-evolution] Rename "guard" to "unless"

[Loïc Lecrenier]

Hi James, 

“guard" is not the opposite of “if”. 
From the Swift book: “You use a guard statement to require that a condition must be true in order for the code after the guard statement to be executed.”
So, unlike “unless”, a “guard" statement must provide an “early exit” in its else clause (fatalError, return, continue, break, …). 
IMO, using “unless” would be less expressive, and encourage more misunderstanding of this feature.

Loïc

> On Jan 6, 2016, at 11:09 AM, James Campbell via swift-evolution <swift-evolution at swift.org> wrote:
> 
> What is "guard"? why its the opposite to "if"!
> 
> So in other languages what have they called this, well in Ruby they called it "unless" which I feel is a much clearer form of intent and lower barrier of entry for a user. See this code.
> 
> guard name != nil else {
>    fatalError("Please enter a name")
> }
> 
> What does that actually say if you look at it from a linguistic point of view, "guard that name doesn't equal nil otherwise fail", that feels very obtuse. 
> 
> With my proposal the syntax could become this:
> 
> unless name != nil {
>   fatalError("Please enter a name")
> }
> 
> This now reads as "unless name doesn't equal nil then fail" which I think is a much clearer syntax. I think this would be a great change for Swift 3. For me I think this is more friendly for beginners.
> 
> It would support the same structure as an if block:
> 
> unless name != nil {
> }
> else
> {
> }
> 
> Going forward it would allow us to be more flexible if we added inline if/unless statement, as in Ruby.
> 
> callThisMethod() if age > 0
> throwThisError() unless age <= 0
> 
> -- 
>  Wizard
> james at supmenow.com
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