{"id":23540,"date":"2018-11-29T16:43:50","date_gmt":"2018-11-29T21:43:50","guid":{"rendered":"https:\/\/mjtsai.com\/blog\/?p=23540"},"modified":"2018-11-29T16:43:50","modified_gmt":"2018-11-29T21:43:50","slug":"lifting-the-self-or-associated-type-constraint-on-swift-existentials","status":"publish","type":"post","link":"https:\/\/mjtsai.com\/blog\/2018\/11\/29\/lifting-the-self-or-associated-type-constraint-on-swift-existentials\/","title":{"rendered":"Lifting the “Self or associated type” Constraint on Swift Existentials"},"content":{"rendered":"

Alexis Gallagher<\/a> (tweet<\/a>):<\/p>\n

“PAT” is an acronym for Protocol with Associated Type. I coined the term in 2015 in a talk<\/a> at the Swift functional programming conference that year.<\/p>\n

That talk is a sort of a mirror of the confusion of Swift devs like myself at the time, who were excited about Swift protocols and your WWDC talk about protocol-oriented programming but also quite surprised by the limitations concerning associated types. I guessed at the motivations for this aspect of the language, relating it to other languages and to your talk. This was in the days before Swift was open-sourced, when we couldn’t just ask about these things.<\/p>\n

I suspect many people, like me, are still a bit confused about the fundamental reason for these limitations.<\/p>\n

[…]<\/p>\n

Fwiw, I am sure the essential reason for the confusion then was that prototocols with associated types behaved almost exactly unlike protocols in objective-c, which was most everyone’s reference point.<\/p><\/blockquote>\n\n

Dave Abrahams<\/a>:<\/p>\n

I agree that the reference point of protocols in Objective-C was probably a source of confusion. However, I think the bigger source of confusion is that we have one thing called protocol<\/code> that<\/p>\n