Should we add this to the list of things requested that will be rejected ?
Yes, if you send a good PR adding it, I’ll merge it. Note that it was (very briefly) named “unless” as a placeholder until May 1, 2015. We carefully bikeshedded this and settled on guard.
-Chris
···
On Jan 6, 2016, at 7:05 AM, James Campbell via swift-evolution <swift-evolution@swift.org> wrote:
On Wed, Jan 6, 2016 at 10:58 AM, Greg Parker <gparker@apple.com <mailto:gparker@apple.com>> wrote:
> On Jan 6, 2016, at 2:09 AM, James Campbell via swift-evolution <swift-evolution@swift.org <mailto:swift-evolution@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`guard` is not the opposite of `if`. `guard` has effects that `if` does not. We deliberately chose not to provide syntax that was identical to `if not X`.
History: The very first proposal of this feature was called `unless`. Fifty-odd messages of discussion later it was called `require`, in part because we did not want to match the `if not` constructs seen in languages like Perl and Ruby. That name was still controversial. A few weeks later it was changed to `guard..else` to general acclaim because the intended use is commonly known as a "guard clause".
--
Greg Parker gparker@apple.com <mailto:gparker@apple.com> Runtime Wrangler--
Wizard
james@supmenow.com <mailto:james@supmenow.com>
+44 7523 279 698
_______________________________________________
swift-evolution mailing list
swift-evolution@swift.org <mailto:swift-evolution@swift.org>
https://lists.swift.org/mailman/listinfo/swift-evolution