[swift-evolution] [swift-evolution-announce] [Review] SE-0041: Updating Protocol Naming Conventions for Conversions

[Brent Royal-Gordon]

> UPDATED APPROACH
> 
> Our updated approach focuses on the two most important conventions: one for initialization and one for representation.
> 
> 1. `Initializable`
> 
> `Initializable` designates protocols that convert *from* a type or from an associated type mentioned in the protocol name, such as the current `<Type>LiteralConvertible` protocols.  This convention would include member requirements for initializers, factory methods, and any other way an instance can be imported to establish a new instance of the conforming type.
> 
> For example, conforming to `ArrayLiteralInitializable` would allow a set to be created with `Set(arrayLiteral: <some array>)` and `var set: Set<T> = []`.
> 
> This phrase replaces the `Creatable` form from our original proposal.
> 
> 2. `Representable`
> 
> `Representable` designates protocols whose primary purpose is to project *to* a type or associated type mentioned in the protocol name.  Items in the standard library that would be subsumed into this naming include `CustomStringConvertible`, `CustomDebugStringConvertible`, and `RawRepresentable`, which we imagine would become `CustomStringRepresentable`, `CustomDebugStringRepresentable`, and (as current) `RawRepresentable`.
> 
> This second category groups together the `Convertible` and `Representable` categories from our original proposal and is predicated on the feedback from the design team review. The `Representable` designation does not promise bidirectional conversion although some `Representable` protocols may include requirements to allow attempted initialization *from* the type of the representation. Doing so falls outside the naming contract we are proposing. 

If we're doing this, I wonder if category 1 shouldn't just be `Convertible`. This would preserve our `LiteralConvertible` protocols with the same names (which, consistency issues aside, seem perfectly cromulent), while shifting the `StringConvertible` protocols over to the `Representable` category.

-- 
Brent Royal-Gordon
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