[swift-users] Type inference of array element type
Rien at Balancingrock.nl
Fri Mar 24 05:30:30 CDT 2017
Btw, I just looked it up and it seems to me that inference only works for literals. Which probably means that tuples are out.
> 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.
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>> On 24 Mar 2017, at 11:08, Toni Suter via swift-users <swift-users at swift.org> wrote:
>> 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,
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>> swift-users at swift.org
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