Creating ranges over mutable, const, or immutable data structures.

[Ali Çehreli via Digitalmars-d-learn]

On 05/24/2014 10:02 AM, w0rp wrote:

 > 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.

How timely! :) Jonathan Crapuchettes talked about facing the same issue 
in his talk at DConf. Perhaps he will post his WrapMutability template 
here or you can wait for his talk on YouTube.

Ali