Re: [swift-evolution] Why doesn't removeLast() on Collection return an optional?

2016-10-20 Thread Alexis via swift-evolution 
I’m fairly confident the author of the collection has to make those checks for 
memory-safety, but in theory there’s wins in only doing the check once, and as 
early as possible. Smaller values to pass, and less checks. 

This is definitely micro-micro-optimization, though. Unlikely to matter for 
most cases.

> On Oct 18, 2016, at 6:00 PM, Max Moiseev via swift-evolution 
>  wrote:
> 
> Yes, if the author of the collection you’re using performs the check in 
> `removeLast`, but they don’t have to.
> 
>> On Oct 18, 2016, at 1:28 PM, Jean-Daniel  wrote:
>> 
>> 
>>> Le 17 oct. 2016 à 23:20, Max Moiseev via swift-evolution 
>>>  a écrit :
>>> 
>>> Hi Louis,
>>> 
>>> I believe, sometimes there are situations where you know for sure that your 
>>> collection is not empty. Maybe you are already in the context where the 
>>> check has been performed. In these cases there is no reason you’d have to 
>>> pay the price of an emptiness check once again.
>> 
>> You have to pay the price anyway, as the check has to be performed to decide 
>> if the software should abort.
>> 
>> 
> 
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Re: [swift-evolution] Why doesn't removeLast() on Collection return an optional?

2016-10-18 Thread Max Moiseev via swift-evolution 
Yes, if the author of the collection you’re using performs the check in 
`removeLast`, but they don’t have to.

> On Oct 18, 2016, at 1:28 PM, Jean-Daniel  wrote:
> 
> 
>> Le 17 oct. 2016 à 23:20, Max Moiseev via swift-evolution 
>>  a écrit :
>> 
>> Hi Louis,
>> 
>> I believe, sometimes there are situations where you know for sure that your 
>> collection is not empty. Maybe you are already in the context where the 
>> check has been performed. In these cases there is no reason you’d have to 
>> pay the price of an emptiness check once again.
> 
> You have to pay the price anyway, as the check has to be performed to decide 
> if the software should abort.
> 
> 

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Re: [swift-evolution] Why doesn't removeLast() on Collection return an optional?

2016-10-18 Thread Jean-Daniel via swift-evolution 

> Le 17 oct. 2016 à 23:20, Max Moiseev via swift-evolution 
>  a écrit :
> 
> Hi Louis,
> 
> I believe, sometimes there are situations where you know for sure that your 
> collection is not empty. Maybe you are already in the context where the check 
> has been performed. In these cases there is no reason you’d have to pay the 
> price of an emptiness check once again.

You have to pay the price anyway, as the check has to be performed to decide if 
the software should abort.


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Re: [swift-evolution] Why doesn't removeLast() on Collection return an optional?

2016-10-17 Thread Louis D'hauwe via swift-evolution 
I understand, pull request has been made. 
https://github.com/apple/swift/pull/5333 


> On 17 Oct 2016, at 23:20, Max Moiseev  wrote:
> 
> Hi Louis,
> 
> I believe, sometimes there are situations where you know for sure that your 
> collection is not empty. Maybe you are already in the context where the check 
> has been performed. In these cases there is no reason you’d have to pay the 
> price of an emptiness check once again.
> 
> Perhaps, it should be documented better, as in “popLast should generally be 
> preferred since it is safer to use. You should only opt for the removeLast if 
> you are certain the collection is not empty and performance is an issue”.
> 
> If you agree, mind sending us a pull request with such a documentation change?
> 
> Thanks!
> Max
> 
>> On Oct 17, 2016, at 2:19 PM, Louis D'hauwe > > wrote:
>> 
>> I see, the really issue I'm trying to bring up is that removeLast() can 
>> easily fail (and result in a fatal error).
>> And unless you read the documentation, that's not very obvious.
>> 
>> Maybe another approach would be to make removeLast() throw an exception if 
>> the collection is empty?
>> That way you can use "try" to safely remove the last item of a collection.
>> 
>> The reasoning behind this is that right now, to safely use removeLast(), you 
>> pretty much have to do something like this:
>> if !collection.isEmpty {
>>  collection.removeLast()
>> }
>> 
>> Having this method throw would allow to change the above to:
>> try collection.removeLast()
>> 
>> – Louis D'hauwe
>> 
>>> On 17 Oct 2016, at 22:52, Max Moiseev >> > wrote:
>>> 
>>> You can use popLast, that does exactly that: 
>>> https://github.com/apple/swift/blob/master/stdlib/public/core/BidirectionalCollection.swift#L213
>>>  
>>> 
>>> 
>>> Max
>>> 
 On Oct 17, 2016, at 1:14 PM, Louis D'hauwe via swift-evolution 
 mailto:swift-evolution@swift.org>> wrote:
 
 Regarding the removeLast() function on Collection:
 
 The current implementation 
 
  is:
 @discardableResult
 public mutating func removeLast() -> Iterator.Element {
let element = last!
self = self[startIndex..>>>return element
 }
 
 This makes it so that if you call removeLast() on an empty collection you 
 get a fatal error.
 ("fatal error: can't remove last element from an empty collection")
 
 The documentation for removeLast() 
 
  even has this noted:
 "The collection must not be empty.".
 
 Surely you could just remove the explicit unwrapping of 'last' and add a 
 guard statement? 
 
 As such:
 @discardableResult
 public mutating func removeLast() -> Iterator.Element? {
guard let element = last else {
return nil
}
self = self[startIndex..>>>return element
 }
 
 It sure seems more "Swifty" to alert at compile time that removing the 
 last item of a collection might fail, and make it return nil as a result.
 
 – Louis D'hauwe
 
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 swift-evolution@swift.org 
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>>> 
>> 
> 

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Re: [swift-evolution] Why doesn't removeLast() on Collection return an optional?

2016-10-17 Thread Max Moiseev via swift-evolution 
Hi Louis,

I believe, sometimes there are situations where you know for sure that your 
collection is not empty. Maybe you are already in the context where the check 
has been performed. In these cases there is no reason you’d have to pay the 
price of an emptiness check once again.

Perhaps, it should be documented better, as in “popLast should generally be 
preferred since it is safer to use. You should only opt for the removeLast if 
you are certain the collection is not empty and performance is an issue”.

If you agree, mind sending us a pull request with such a documentation change?

Thanks!
Max

> On Oct 17, 2016, at 2:19 PM, Louis D'hauwe  wrote:
> 
> I see, the really issue I'm trying to bring up is that removeLast() can 
> easily fail (and result in a fatal error).
> And unless you read the documentation, that's not very obvious.
> 
> Maybe another approach would be to make removeLast() throw an exception if 
> the collection is empty?
> That way you can use "try" to safely remove the last item of a collection.
> 
> The reasoning behind this is that right now, to safely use removeLast(), you 
> pretty much have to do something like this:
> if !collection.isEmpty {
>   collection.removeLast()
> }
> 
> Having this method throw would allow to change the above to:
> try collection.removeLast()
> 
> – Louis D'hauwe
> 
>> On 17 Oct 2016, at 22:52, Max Moiseev > > wrote:
>> 
>> You can use popLast, that does exactly that: 
>> https://github.com/apple/swift/blob/master/stdlib/public/core/BidirectionalCollection.swift#L213
>>  
>> 
>> 
>> Max
>> 
>>> On Oct 17, 2016, at 1:14 PM, Louis D'hauwe via swift-evolution 
>>> mailto:swift-evolution@swift.org>> wrote:
>>> 
>>> Regarding the removeLast() function on Collection:
>>> 
>>> The current implementation 
>>> 
>>>  is:
>>> @discardableResult
>>> public mutating func removeLast() -> Iterator.Element {
>>> let element = last!
>>> self = self[startIndex..>> return element
>>> }
>>> 
>>> This makes it so that if you call removeLast() on an empty collection you 
>>> get a fatal error.
>>> ("fatal error: can't remove last element from an empty collection")
>>> 
>>> The documentation for removeLast() 
>>> 
>>>  even has this noted:
>>> "The collection must not be empty.".
>>> 
>>> Surely you could just remove the explicit unwrapping of 'last' and add a 
>>> guard statement? 
>>> 
>>> As such:
>>> @discardableResult
>>> public mutating func removeLast() -> Iterator.Element? {
>>> guard let element = last else {
>>> return nil
>>> }
>>> self = self[startIndex..>> return element
>>> }
>>> 
>>> It sure seems more "Swifty" to alert at compile time that removing the last 
>>> item of a collection might fail, and make it return nil as a result.
>>> 
>>> – Louis D'hauwe
>>> 
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>>> swift-evolution mailing list
>>> swift-evolution@swift.org 
>>> https://lists.swift.org/mailman/listinfo/swift-evolution 
>>> 
>> 
> 

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Re: [swift-evolution] Why doesn't removeLast() on Collection return an optional?

2016-10-17 Thread Louis D'hauwe via swift-evolution 
I see, the really issue I'm trying to bring up is that removeLast() can easily 
fail (and result in a fatal error).
And unless you read the documentation, that's not very obvious.

Maybe another approach would be to make removeLast() throw an exception if the 
collection is empty?
That way you can use "try" to safely remove the last item of a collection.

The reasoning behind this is that right now, to safely use removeLast(), you 
pretty much have to do something like this:
if !collection.isEmpty {
collection.removeLast()
}

Having this method throw would allow to change the above to:
try collection.removeLast()

– Louis D'hauwe

> On 17 Oct 2016, at 22:52, Max Moiseev  wrote:
> 
> You can use popLast, that does exactly that: 
> https://github.com/apple/swift/blob/master/stdlib/public/core/BidirectionalCollection.swift#L213
>  
> 
> 
> Max
> 
>> On Oct 17, 2016, at 1:14 PM, Louis D'hauwe via swift-evolution 
>> mailto:swift-evolution@swift.org>> wrote:
>> 
>> Regarding the removeLast() function on Collection:
>> 
>> The current implementation 
>> 
>>  is:
>> @discardableResult
>> public mutating func removeLast() -> Iterator.Element {
>>  let element = last!
>>  self = self[startIndex..>  return element
>> }
>> 
>> This makes it so that if you call removeLast() on an empty collection you 
>> get a fatal error.
>> ("fatal error: can't remove last element from an empty collection")
>> 
>> The documentation for removeLast() 
>> 
>>  even has this noted:
>> "The collection must not be empty.".
>> 
>> Surely you could just remove the explicit unwrapping of 'last' and add a 
>> guard statement? 
>> 
>> As such:
>> @discardableResult
>> public mutating func removeLast() -> Iterator.Element? {
>>  guard let element = last else {
>>  return nil
>>  }
>>  self = self[startIndex..>  return element
>> }
>> 
>> It sure seems more "Swifty" to alert at compile time that removing the last 
>> item of a collection might fail, and make it return nil as a result.
>> 
>> – Louis D'hauwe
>> 
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>> swift-evolution mailing list
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>> https://lists.swift.org/mailman/listinfo/swift-evolution
> 

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Re: [swift-evolution] Why doesn't removeLast() on Collection return an optional?

2016-10-17 Thread Dave Abrahams via swift-evolution 

on Mon Oct 17 2016, Louis D'hauwe  wrote:

> Regarding the removeLast() function on Collection:
>
> The current implementation
> 
> is:
> @discardableResult
> public mutating func removeLast() -> Iterator.Element {
>   let element = last!
>   self = self[startIndex..   return element
> }
>
> This makes it so that if you call removeLast() on an empty collection you get 
> a fatal error.
> ("fatal error: can't remove last element from an empty collection")
>
> The documentation for removeLast()
> 
> even has this noted:
> "The collection must not be empty.".
>
> Surely you could just remove the explicit unwrapping of 'last' and add a 
> guard statement? 
>
> As such:
> @discardableResult
> public mutating func removeLast() -> Iterator.Element? {
>   guard let element = last else {
>   return nil
>   }
>   self = self[startIndex..   return element
> }
>
> It sure seems more "Swifty" to alert at compile time that removing the last 
> item of a collection
> might fail, and make it return nil as a result.

see the popLast() method.

-- 
-Dave

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Re: [swift-evolution] Why doesn't removeLast() on Collection return an optional?

2016-10-17 Thread Max Moiseev via swift-evolution 
You can use popLast, that does exactly that: 
https://github.com/apple/swift/blob/master/stdlib/public/core/BidirectionalCollection.swift#L213
 


Max

> On Oct 17, 2016, at 1:14 PM, Louis D'hauwe via swift-evolution 
>  wrote:
> 
> Regarding the removeLast() function on Collection:
> 
> The current implementation 
> 
>  is:
> @discardableResult
> public mutating func removeLast() -> Iterator.Element {
>   let element = last!
>   self = self[startIndex..   return element
> }
> 
> This makes it so that if you call removeLast() on an empty collection you get 
> a fatal error.
> ("fatal error: can't remove last element from an empty collection")
> 
> The documentation for removeLast() 
> 
>  even has this noted:
> "The collection must not be empty.".
> 
> Surely you could just remove the explicit unwrapping of 'last' and add a 
> guard statement? 
> 
> As such:
> @discardableResult
> public mutating func removeLast() -> Iterator.Element? {
>   guard let element = last else {
>   return nil
>   }
>   self = self[startIndex..   return element
> }
> 
> It sure seems more "Swifty" to alert at compile time that removing the last 
> item of a collection might fail, and make it return nil as a result.
> 
> – Louis D'hauwe
> 
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[swift-evolution] Why doesn't removeLast() on Collection return an optional?

2016-10-17 Thread Louis D'hauwe via swift-evolution 
Regarding the removeLast() function on Collection:

The current implementation 

 is:
@discardableResult
public mutating func removeLast() -> Iterator.Element {
let element = last!
self = self[startIndex..https://github.com/apple/swift/blob/c3b7709a7c4789f1ad7249d357f69509fb8be731/stdlib/public/core/BidirectionalCollection.swift#L220>
 even has this noted:
"The collection must not be empty.".

Surely you could just remove the explicit unwrapping of 'last' and add a guard 
statement? 

As such:
@discardableResult
public mutating func removeLast() -> Iterator.Element? {
guard let element = last else {
return nil
}
self = self[startIndex..___
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