the protocol error every swift dev hits #programming

Added: 2026-05-17

[00:00:02]Swift doesn't let you do this.

[00:00:05]It says "No dice."

[00:00:07]You try to create this protocol and it'll say, "Hey, an associated type named T must be declared in the protocol or in a protocol it inherits." Now, most developers, we try to write code like this and run into this problem. The implementer is providing the type, whereas a generic, like in this case with this generic syntax here, a generic says, "Hey, the caller gets to decide the type."

[00:00:34]That's the fundamental difference.

[00:00:36]Generics are for the callers to implement and associated types are for the implementers to choose. My take is they're both a variable. It's just who gets to decide what that variable ends up being, the caller or the implementer.