[swift-evolution] Better syntax for deferred?

[John McCall]

> On Jan 4, 2016, at 12:41 PM, Howard Lovatt via swift-evolution <swift-evolution at swift.org> wrote:
> I don’t think it is worth changing from defer to the more traditional try finally block, both have pros and cons. Just work with what we have. You can always, as a matter of style, put a single defer block at the end of scope instead of multiple defers throughout the block.

For what it’s worth, the error-handling rationale discusses the trade-offs of the defer syntax.  I think we’re very happy with the current syntax.

John.

> 
> 
>> On 5 Jan 2016, at 1:17 AM, Jeremy Pereira via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>> 
>>> 
>>> On 2 Jan 2016, at 16:49, Maury Markowitz via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>>> 
>>>> On Jan 2, 2016, at 9:38 AM, Nicky Gerritsen <nickygerritsen at me.com <mailto:nickygerritsen at me.com>> wrote:
>>>> 
>>>> Defer is used to make code *always* run, even if the function terminates early. Imagine:
>>> 
>>> Which is precisely why I called it 'always'. So in your example:
>>> 
>>>   func doSomethingWith(x: Int) {
>>> 	print(“1”)
>>> 	defer { print(“2") }
>>> 	if x > 3 { defer { print(“yay”); return }
>>> 	print(“3”)
>>>   }
>>> 
>>> I would say:
>>> 
>>>   func doSomethingWith(x: Int) {
>>> 	print(“1”)
>>> 	print(“3”)
>>>       always {
>>>           print(“2")
>>>           if x > 3 { print(“yay”) }
>>>       }
>>>   }
>>> 
>>> This is functionally identical, but both the syntax and program flow are greatly improved.
>> 
>> No your example is not functionally identical to Nicky’s (notwithstanding the missing closing brace in the original). “defer" defers the closure to the end of the current scope. In this instance , that is the end of the if block. The “yay” must come before the “2” because the if scope exits before the function scope. Also, in the following:
>> 
>> func doSomethingWith(x: Int) {
>>    print("1")
>>    defer { print("2") }
>>    if x > 3 { defer { print("yay") } }
>>    print("3")
>> }
>> 
>> doSomethingWith(4)
>> 
>> “yay” comes before “3” for the same reason.
>> 
>> 
>>> 
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>> 
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