One of the things that threw me when starting with Swift was the inability to
use many protocols as types, e.g- being unable to declare: [SequenceType],
instead having to do: [AnySequence]
And I guess it got me wondering; why can’t we just have these be auto-generated
and used where we would expect a protocol to fit? Writing type-erased wrappers
currently involves a lot of boilerplate, especially for a type with a lot of
methods and/or properties, so automating this would be very useful.
For me there are two good options:
Autogenerate for All Types: As it says; every protocol would have an
identically named type-erasure (with the same visibility etc.) that Swift would
just swap in where appropriate. For example:
protocol Foo { … }
let myArray:[Foo] // Array of type-erased wrappers of Foo
Autogenerate by Attribute: Same basic idea, except that an attribute would be
required to specify which protocols get automatic type-erasure like so:
@autoErasure protocol Foo { … }
let myArray:[Foo] // Array of type-erased wrappers of Foo
I’m curious for people’s thoughts on the matter. I know that I for one am tired
of defining type-erased wrappers that are just a heap of boiler-plate to
properly wrap an instance. It’s also something I’ve seen people doing wrong
(and done wrong myself), for example by using closures to invoke methods on an
instance; this is a much more elegant looking solution but very quickly bloats
the size of the type-erased wrapper compared to more correct boxing method
(though for single method protocols it may be fine). It seems like something
that would be good to take out of the hands of developers who mostly don’t want
to have to define these in the first place, though of course the capability to
defining customised versions would remain if anyone actually needs it.
I’m particularly curious about other features in discussion or that are
upcoming that may affect this, as I’m sure I’ll have missed some. Anything that
might render this obsolete (or less necessary)? Also whether anyone thinks it
could be a bad idea to essentially hide the type-erasure._______________________________________________
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