Comment by adrianmsmith
13 hours ago
One thing I think generics in Go is missing is the <?> concept in Java.
If you're taking a List[T] and all you want to do is to call list.size() then you don't care what type of list it is. In Java you can write a function which takes a List<?> but in Go you have to write List[T] so then the question becomes what is T? You have to make the function (or type you're a method on) generic. If you make the type generic then every user of your type also needs to specify T, etc.
I don't think it would be impossible to add that to Go. Allow List[?], which matches a List with any type parameter. Calling functions which don't involve the type parameter like list.size() would be fine, calling a method returning the type parameter like list.get(n) would return "any", and methods taking the type parameter like list.set(n, obj) would probably not be callable.
You need this in Java because interfaces are explicitly implemented. You don't need this in Go because interfaces are structurally implemented. The way you spell "anything that has a method named Size which returns int" is interface{Size() int}.
Go Generics work differently than those in Java. They are specialized, meaning that they are not generic at runtime anymore. Instead, the compiler creates a different implementation for each type.
At runtime, there are only List[int], List[string], etc. List[T] is not a thing anymore.