[swift-users] Type inference of array element type

Rien Rien at Balancingrock.nl
Fri Mar 24 05:22:36 CDT 2017

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:
> 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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