Right here’s a cool little problem introduced up this morning by a good friend. Think about the next code:
swap foo {
case .a: return "a"
case .b(let str) the place str.hasPrefix("c"), .c: return "c"
case .b: return "b"
}
It gained’t compile.
While you bind a logo for one sample, you should bind that image for each sample in a case. This prevents you, for instance, from binding str in a single sample after which making an attempt to make use of str within the shared case physique. For instance, think about this case. What would you anticipate to occur when foo is .c?
func switchTheFallthroughOrder(foo: Foo) -> String {
swap foo {
case .a: return "a"
case .b(let str) the place str.hasPrefix("c"), .c:
// Utilizing `str` right here is unhealthy!
print(str)
return "c"
case .b: return "b"
}
}
Regardless of my first knee-jerk refactoring, shifting out the .c case to make use of fallthrough doesn’t work. Once more, it’s because str just isn’t sure for .c and may be used within the successive case physique:
Nonetheless, as Greg Titus identified, in the event you swap the order to make use of the binding case first with fallthrough, Swift is aware of at compile time that the binding gained’t keep it up past that scope. This resolves the error, since str is barely used within the the place clause to slim the sample matching:
Additional, when utilizing bindings in case exams, a waterfall strategy the place the sure gadgets are used earlier than fallthrough can prolong by a number of steps with the blessing of the compiler:
case .widest(let first, let second) the place first.satisfiesACondition():
// can use `first`, `second` right here
fallthrough
case .medium(let second) the place second.satisfiesAnotherCondition():
// can use `second` right here even when it was sure
// through `widest` above through fallthrough
fallthrough
case .narrowest: return someValue
My due to Greg Titus for figuring this all out!
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