> On Nov 11, 2016, at 1:37 PM, Nevin Brackett-Rozinsky via swift-evolution
> <[email protected]> wrote:
> I’ll mention this here since it’s related to tuples and optionals. Starting
> with this setup:
>
> var x, y: Int?
> func f() -> (Int, Int) { return (0, 1) }
>
> This fails to compile:
>
> (x, y) = f() // Error: Cannot express tuple conversion '(Int, Int)' to
> '(Int?, Int?)'
>
> But this works fine:
>
> func g() -> Int { return 2 }
> (x, y) = (g(), g())
>
> What is going on, why does the first one fail, and is this a bug or does it
> need a proposal to fix?
It's a bug. The error message is actually subtly telling you the problem: the
type-checker literally can't express the opaque tuple conversion in the AST;
when it's a raw tuple expression, it can push the element conversions into the
element expressions, but it can't do that with an opaque tuple. It's a silly
restriction because of an unfortunate representational decision.
John.
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