Can anyone please shed light into this? Seems Java interop issues

class Foo<T> {
    fun <T> foo(a: T, b: T) = a == b // compiles
}

class MyCallback<T> : DiffUtil.ItemCallback<T>() {
    override fun areItemsTheSame(oldItem: T, newItem: T): Boolean =
        throw Error("TODO")

    override fun areContentsTheSame(oldItem: T, newItem: T): Boolean =
        oldItem == newItem // Doesn't compile - "equals in not implemented on T"
}

What about

MyCallback<T : Any>

?

So I don’t know why it doesn’t compile for you, as it does for me 🤷‍♂️🏻 . But there is definitely a difference between those two functions:

println(MyCallback<String>().areContentsTheSame("a", "b"))
println(Foo<Int>().foo<String>("a", "b"))

As you can see the

T

of

Foo.foo()

is a different than the

T

of

Foo

. Thats not possible in the

MyCallback

implementation.

@Kune Keiseiie I remember trying with

Any

and it didn't change anything, weirdly

No, and unfortunately I can’t reproduce your error: https://pl.kotl.in/pKgRjxlHh

may it be because the callback I'm extending was declared in Java? This is why I attributed it to java interop...

It looks like this issue is specific to DiffUtil and is really just a lint warning not a "real" compiler error. The reason is the default equality operator checks if the object references are the same and the whole purpose of DiffUtil is to check that they represent the same data because the list changed and all the objects are technically different even if nothing changed. If T is limited to a class that overrides equals() this error goes away. https://issuetracker.google.com/issues/116789824