[swift-users] Associatedtype Naming Conventions

Karl Wagner razielim at gmail.com
Tue Jun 6 18:47:54 CDT 2017

> On 7. Jun 2017, at 00:25, Dave Abrahams via swift-users <swift-users at swift.org> wrote:
> on Wed May 31 2017, Steven Brunwasser <swift-users-AT-swift.org <http://swift-users-at-swift.org/>> wrote:
>> Yes, I understand this. I was just wondering if there was a naming
>> convention I should use to differentiate them.
> I would try to find something more specific and descriptive than
> “Container” and “Element” if you think there's a chance they would ever
> arise as associated types of the same type but with distinct identity.
> Another possibility, if you think that might be about to happen, is that
> you're using conformance when you should use aggregation.  For example,
> an Int has everything it needs to be a Sequence and/or Iterator (n to
> infinity), a Collection (of numbers from zero to its bitWidth), etc.,
> but *should* it conform to those protocols?  IMO probably not.  If you
> find yourself hard pressed to describe what something *is* in a few
> words, it may be conforming to too many protocols.

Additionally, I find that when a type is representable in multiple overlapping ways (where “overlapping” is meant quite broadly), it can be good to create wrappers for those conformances.

For example, you might try:

Struct MyThing {

extension MyThing {

    var foo: Foo { return MyThing.FooWrapper(self) }
    var bar: Bar { return MyThing.BarWrapper(self)  }

    struct FooWrapper: Foo {
        let base: MyThing
        init(_ wrapping: MyThing) { self.base = wrapping }

        // Implement ‘Foo’ using data from ‘base’.

let something = MyThing()


This is analogous to how String is represented — the data is stored once, and there are multiple Collection conformances which interpret the data in different ways (as graphemes, or as a collection of non-character-boundary code-units in various encodings).
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