[swift-users] Type inference of array element type

[Rien]

I always yield to proof ;-)

hope someone more knowledgable chips in...

Regards,
Rien

Site: http://balancingrock.nl
Blog: http://swiftrien.blogspot.com
Github: http://github.com/Balancingrock
Project: http://swiftfire.nl





> On 24 Mar 2017, at 11:53, Toni Suter <tonisuter at me.com> wrote:
> 
> Hmm, I don't know. It also works with other nominal types. For example:
> 
> struct S {
>   var x: Int
>   var y: Int
> }
> let s1 = S(x: 0, y: 1)
> let s2 = S(x: 2, y: 3)
> let arr = [s1, nil, s2]
> print(type(of: arr)) 		// Array<Optional<S>>
> 
>> Am 24.03.2017 um 11:30 schrieb Rien <Rien at Balancingrock.nl>:
>> 
>> Btw, I just looked it up and it seems to me that inference only works for literals. Which probably means that tuples are out.
>> 
>> Regards,
>> Rien
>> 
>> Site: http://balancingrock.nl
>> Blog: http://swiftrien.blogspot.com
>> Github: http://github.com/Balancingrock
>> Project: http://swiftfire.nl
>> 
>> 
>> 
>> 
>> 
>>> On 24 Mar 2017, at 11:22, Rien via swift-users <swift-users at swift.org> wrote:
>>> 
>>> IMO this is a boundary problem.
>>> How far do you want to go in letting the compiler deduce the actual type?
>>> It is possible to make very elaborate constructs that would basically default to a complex tuple/array/dictionary construct with only Any?’s in them. (well, the dict would require a Hashable too)
>>> 
>>> Besides, the recent discussion on compile times illustrates another angle to this problem: if type inference is used extensively, compile times go to infinite…
>>> 
>>> So while I do not know if this is a bug or not, I would recommend not to use it anyhow.
>>> 
>>> Regards,
>>> Rien
>>> 
>>> Site: http://balancingrock.nl
>>> Blog: http://swiftrien.blogspot.com
>>> Github: http://github.com/Balancingrock
>>> Project: http://swiftfire.nl
>>> 
>>> 
>>> 
>>> 
>>> 
>>>> On 24 Mar 2017, at 11:08, Toni Suter via swift-users <swift-users at swift.org> wrote:
>>>> 
>>>> Hi,
>>>> 
>>>> If I declare a variable and initialize it with an array literal whose elements are integer literals and nil literals,
>>>> the compiler will infer the type Array<Optional<Int>> for that variable:
>>>> 
>>>> let arr = [1, nil, 3]
>>>> print(type(of: arr)) 	// Array<Optional<Int>>
>>>> 
>>>> However, that only works with nominal types such as Int and String. If I do the same thing with an array of tuples,
>>>> I get a compile error:
>>>> 
>>>> let arr = [(1, false), nil, (3, true)]		// error: type of expression is ambiguous without more context
>>>> print(type(of: arr))
>>>> 
>>>> Why can't the compiler infer the type Array<Optional<(Int, Bool)>> in this example? Is there a reason for this or is it a bug?
>>>> 
>>>> Thanks and best regards,
>>>> Toni
>>>> 
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>>> 
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>> 
>