# Lifting the "Self or associated type" constraint on existentials **URL:** \ **Category:** Pitches\ **Created:** [November 15, 2018, 10:13pm UTC](https://forums.swift.org/t/lifting-the-self-or-associated-type-constraint-on-existentials/18025 "2018-11-15T22:13:59Z")\ **Posts on this page:** 1\ **Showing post:** 45
**Author:** ![algal](https://sea2.discourse-cdn.com/swift/user_avatar/forums.swift.org/algal/32/4797_2.png) [@algal](https://forums.swift.org/u/algal)\ **Post date:** [November 25, 2018, 4:53am UTC](https://forums.swift.org/t/lifting-the-self-or-associated-type-constraint-on-existentials/18025/45 "2018-11-25T04:53:23Z")
> [@dabrahams](#): > > FWIW, I don't know the term “PAT.” “PAT” is an acronym for Protocol with Associated Type. I coined the term in 2015 in a talk at the Swift functional programming conference that year ( [https://youtu.be/XWoNjiSPqI8](https://youtu.be/XWoNjiSPqI8) ). 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. I suspect many people, like me, are still a bit confused about the fundamental reason for these limitations. I’d still like to understand it better! (For instance, I am embarrassed to admit, I doubt I could define “existential” to my satisfaction. I bet I’m not the only one.) 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. I suspect this is the same thing which you are saying more precisely now, when you distinguish protocols-for-defining-constraints and protocols-for-type-erasure, but I’m not sure. --- _[View the full topic](https://forums.swift.org/t/lifting-the-self-or-associated-type-constraint-on-existentials/18025)._