Hi Austin,
let me repeat the example so that clarify my point from this example.
protocol cannot do this:
func input(value: ProtocolForABC) {
print(value.someCommonProperty)
if value is A {
} else if value is B {
} else if value is C {
} else {
// There no other cases, but compiler will not trigger a warning.
}
}
The compiler will not know your protocol is only conformed to these three
classes.
So the else block will not trigger a warning.
- Jiannan
> 在 2016年5月16日，18:37，Austin Zheng <[email protected]> 写道：
>
> I'm sorry, but I don't understand the point you are trying to make.
>
> If you pass in a value of type (A | B | C) to a function, what might you want
> to do with that value?
>
> If you want to do one thing if the value is type A, something else if the
> value is type B, and something else if the value is type C, then you need to
> switch or otherwise type check the value at runtime. You can't get around
> this, no matter whether you use enums, protocols, generics, or union type.
>
> If you want it to do something that A, B, and C all support, use a generic
> and/or a protocol. In this case limiting the inputs to only those three types
> is probably a design smell. The whole point of a shared interface is that it
> only matters that the interface is properly implemented by a type, not what
> that type is.
>
> If you don't care about doing anything with the value, just make your
> function generic: func<T>(input: T).
>
> Austin
>
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