> On Jan 6, 2016, at 7:16 PM, Don Wills via swift-users <swift-users@swift.org>
> wrote:
>
> Swift method lookup obviously chose the second mth func if it exists, but why?
>From the behavior here, it looks like the compiler is first looking for a
>matching method, then if it can’t find one it unwraps the optional parameter
>and looks for a match again. So in this case it immediately finds a match (the
>second mth) and doesn’t try unwrapping the String! parameter.
I have no idea whether that’s correct/intentional behavior, or a bug. I do know
that function overloading can create weird situations in any language that
supports it (notably C++), so I’m not surprised that there are some edge cases
in Swift too.
> I really don't understand optionals.
Well, think of the declaration of s1 as being
private var s1 : Optional<String>
which is what it actually is under the hood. That makes it pretty clear that
the 2nd mth method is the one that will get called. The confusion comes in when
you also consider that the compiler will implicitly deref an Optional<String>
to String if it’s been declared using “!”, in which case the first mth can be
called. Now it’s sort of ambiguous which is preferable.
—Jens_______________________________________________
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