A graph data structure usable in @safe pure nothrow functions

[w0rp via Digitalmars-d]

I just added @nogc support to the map and graph types, with 
fallback behaviour for older D compiler versions. I used this.

static if(__VERSION__ < 2066) { enum nogc = 1; }

So as long as I write @nogc left of other attributes, it will 
compile the library on both DMD 2.065 and DMD 2.066.

Now every range, get, and remove function on the maps and graphs 
can be used in @nogc functions, because these functions never 
allocate more memory on the garbage collected heap.