[swift-users] Type inference of array element type

[Toni Suter]

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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>>> swift-users at swift.org
>>> https://lists.swift.org/mailman/listinfo/swift-users
>> 
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> 

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