[Pitch] Primary Associated Types in the Standard Library

[lorentey (Karoy Lorentey)]

@benrimmington

It might be worth grouping the table, into protocols which are

1. Candidates for this proposal:

• they declare or inherit associated types.

2. Not applicable:

• they currently don't have associated types;
• marker protocols ( Sendable and UnsafeSendable );
• type aliases ( Unicode.Encoding and Unicode.Parser ).

Good idea -- I updated the original post accordingly. I also listed the rest of the associated types for each protocol. (Check out the list on StringProtocol. )

Note that Unicode.Encoding and Unicode.Parser are considered public protocols that currently happen to be typealiases to underscored protocol definitions, for very annoying technical reasons. (Which we should eventually get around to resolving...)

@benrimmington

Are KeyedEncodingContainerProtocol and KeyedDecodingContainerProtocol commonly used?

No -- in fact, given that Encoder/Decoder sadly forces these into type-erased boxes, there is very little reason for anyone to write generic functions over them. Therefore, there is no reason for these to have a primary associated type.

I updated the table accordingly.