missing == for Reverse

[johnnychen94]

That they don't "equal" is strange...

julia> A = [1 2 3]
1×3 Matrix{Int64}:
 1  2  3

julia> Iterators.Reverse(A) == reverse(A)
false

julia> all(map(==, Iterators.Reverse(A), reverse(A)))
true

[mcabbott]

Isn't this true for all generators?

julia> (x for x in A) == A
false

julia> all(map(==, (x for x in A), A))
true

[johnnychen94]

Ah, I didn't realize that this is a general case. I think we should document this as undefined behavior. More eagerly, it also makes sense to throw an error or depwarn on this.

One reason I can think of not defining this is that iterate is not always a trivial operation. But for some special cases, like Reverse I mentioned, Base.(:)(r1::Reverse, r2::Reverse) = r1.itr == r2.itr is a good definition.

Some generators, e.g., ranges, do apply ==.

[mcabbott]

Ranges are AbstractVectors though. For generators I don't know what the ideal behaviour would be, agree it's a little weird.

xref #37648, which may make this more confusing.