I have been writing my own hashmap which can provide forward
ranges usable in @safe pure nothrow functions, because it's going
to be useful for creating graph data structures with the same. I
came to writing my ranges and I figured out how to do everything
right for just mutable hashmaps, but I have no idea how to manage
the tail-const nature of ranges in a variety of combinations. I
figured out that I need to satisfy the following constraints.
Create a mutable KeyRange over a map which forwards on the right
constness for the key type, so the following must be true.
HashMap!(K, V).keys.front -> K
const(HashMap!(K, V)).keys.front -> const(K)
immutable(HashMap!(K, V)).keys.front -> immutable(K)
I have encounted some difficulty in trying to write a range which
does this.
