[swift-evolution] [Proposal] Remove eager `map` and `filter`

[Brent Royal-Gordon]

> 1. Make sure that
> 
> Array(sequence.lazy.map { ... })   and   sequence.map { ... }
> Array(sequence.lazy.filter { ... })   and   sequence.filter { ... }
> 
> are just as fast (with -O). "Fix lazy filter" proposal should help with this.
> 
> 2. Remove eager `map` and `filter`
> 
> 3. Remove `lazy` property
> 
> sequence.map { ... }  will call lazy `map`, which is at least as fast as eager version
> 
> 4. Re-add `array` property to LazySequence
> 
> So that we can more easily convert to multipass sequence when needed.

The first three Swift 1 betas were this way; then the lazy higher-order functions were changed to the current design, apparently because the all-lazy solution was confusing. (It's also worth noting that if we had only lazy versions, they could not take @noescape.) So I don't really think this is going to fly.

-- 
Brent Royal-Gordon
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