[swift-evolution] [Proposal Draft] automatic protocol forwarding

plx plxswift at icloud.com
Wed Dec 30 10:06:18 CST 2015

Thanks for writing this up.

Some quick points.

Firstly, I think it is best if the `init(_ forwardeeReturnValue: Forwardee)`-style initializer be replaced by something with a distinctly-named argument, e.g. `init(forwardeeReturnValue value: Forwardee)`. 

For use with actual wrapper types the “init(_ wrappedValue: Wrapped)`-style init is too valuable to “claim” for this purpose (in particular b/c we may want to “adjust" the forwarded result); it’s IMHO better if we use a distinct `init` for the forwardee-return-value scenario so we know where the value is coming from.

Secondly, I would prefer partial-forwarding be given more consideration, b/c it seems somewhat common for me in practice at this time.

EG: I would do the following somewhat frequently:

struct FooIdentifier: Equatable, Comparable, Hashable

class Foo {
  let identifier: FooIdentifier
  let name: String

  forward Hashable to identifier

func ==(lhs: Foo, rhs: Foo) -> Bool {
  return lhs.identifier == rhs.identifier && lhs.name == rhs.name

…even though I agree that full-forwarding would the most-common scenario.

I have a few other similar cases involving non-standard-library types but they all fit the same basic pattern as above for `Hashable`.

Finally, I’m actually at a bit of a loss for too many uses for the generic forwarding mechanism; if it was added I’d use it to streamline some wrapper types, but beyond that I’m not seeing all that many places where I’d do much more than that with this feature if added.

Any chance at adding a few more-concrete motivating examples for the fancier cases?

> On Dec 29, 2015, at 10:37 AM, Matthew Johnson via swift-evolution <swift-evolution at swift.org> wrote:
> I have completed a first draft of a proposal to introduce automatic protocol forwarding.  I’m looking forward to feedback from everyone!

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