Swift will infer types from the context of an expression as well as the inputs.
In this case, although 'Int' and 'String' do not share a type, they are both
convertible to 'Any', the argument to 'print'. So because of the call to
'print', 'T' becomes 'Any', and the expression becomes, essentially
print((t1 as Any?) ?? ("asdf" as Any))
(Actually, the signature of 'print' is a little more complicated than that,
but that's the gist of what's going on.)
Jordan
> On Apr 18, 2016, at 2:51, tuuranton--- via swift-users
> <swift-users@swift.org> wrote:
>
> Why does this compile?
>
> let t1: Int? = 2
> print(t1 ?? "asdf")
>
> The type of ?? is this:
>
> @warn_unused_result
> public func ??<T>(optional: T?, @autoclosure defaultValue: () throws -> T)
> rethrows -> T
>
> The type syas that T must be the same type throughout. But above I could
> successfully use Int? and then String. Why?
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