[swift-evolution] Proposal: 'T(literal)' should construct T using the appropriate literal protocol if possible

John McCall rjmccall at apple.com
Fri Jun 3 20:20:50 CDT 2016

> On Jun 3, 2016, at 5:31 PM, Ben Rimmington via swift-evolution <swift-evolution at swift.org> wrote:
> John McCall wrote:
>> I think that's a very promising way of thinking about literals.  Writing
>> a literal creates a notional value whose type is the informal, infinite-
>> precise type of all integer/FP/collection/etc. literals, which (1) can be
>> implicitly converted to any type that implements the appropriate protocol
>> and (2) in fact *must* be converted to some such type (possibly the
>> default type for that literal) in order for the code to be executable.
> Could you allow IntegerLiteralConvertible.IntegerLiteralType associatedtype
> to override the default Swift.IntegerLiteralType typealias iff there's more
> than one unlabelled init(_:) to choose from? Then you can call the "correct"
> init(_:) instead of calling init(integerLiteral:) as a "special case".

This is essentially already how it works.  The literal protocols are not invoked via
overload resolution; Swift always invokes the initializer that satisfies the protocol

That is, you can provide ten different init(integerLiteral: T) initializers, but that will
just prevent the compiler from inferring the associated type, so you'll have to
declare it.  Once you do, that associated type will determine the initializer that
satisfies the requirement, and that'll always be the initializer chosen.


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