[swift-evolution] Add an ifPresent function to Optional

[Erica Sadun]

Questions being raised in this discussion:

* Are the current stdlib names for optional map and flatMap misleading? 
* Are the current stdlib functions for optional closure application appropriate and sufficient?

    @warn_unused_result
    public func map<U>(@noescape f: (Wrapped) throws -> U) rethrows -> U?

    @warn_unused_result
    public func flatMap<U>(@noescape f: (Wrapped) throws -> U?) rethrows -> U?

Assume there could be up to three stdlib functions just for applying closures to .some-case 
optionals. Would they look like this?

public func f1<U>(@noescape f: (Wrapped) throws -> U) rethrows -> U?
public func f2<U>(@noescape f: (Wrapped) throws -> U!) rethrows -> U!
public func f3<U>(@noescape f: (Wrapped) throws -> U) rethrows -> Void

Right now f2/flatMap returns U?, not U or U!, and won't throw if nil, right? Should it
stay that way or change to something that throws and returns a guaranteed value?
Or maybe the current "f2" model (flatMap)  be discarded and replaced by an 
"ifPresent"-like Void call?

And regardless of which functions are included, what would the appropriate 
names for each function style be?

-- E

> On Mar 20, 2016, at 11:22 AM, Andrey Tarantsov <andrey at tarantsov.com> wrote:
> 
>> No.  My argument is that map on collections and on optionals are two
>> completely different things.  They unify on a level that does not
>> exist in Swift (higher-kinded types).
> 
> +1000.
> 
> Optional.map is already highly unfortunate. It makes optional arrays especially painful to deal with, but even in general, you can no longer glance at the code and see which parts are dealing with many items and which parts are dealing with single items.
> 
> I would definitely support renaming Optional.{map,flatMap}.
> 
> A.
> 

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