[swift-evolution] [Draft] Abolish IUO type

[Brent Royal-Gordon]

> 1. We have to add @implicitly_unwrapped attribute to the proposal. I hate implied "attributes", available only to compiler. The wording needs to be reformulated in terms of this attribute

Agree.

> 2. We need to encourage using the attribute instead of `!`.
> 3. In the future, `!` can be removed entirely and leave only the attribute. But not for now

Disagree. As I mentioned earlier in the thread, IUOs are going to become less common on Apple platforms, but they are here to stay in Swift as a whole.

> In order to do this, I suggest finding a concise name for it. Like @IUO, but possibly more readable

I do agree that we should look for a shorter, better name. I suggest `@autounwrap`, by analogy with `@autoclosure`. Both features insert invisible syntax at usage sites to make an expression of one type appear to be an expression of a different type.

(Actually, I think that `@autoclosure` is a great analogy for this feature in many respects.)

-- 
Brent Royal-Gordon
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