The current signature for std.random.dice() is:

size_t dice(R)(ref R rnd, double[] proportions...); 

Correct me if I'm wrong, but I think it would be trivial to change it to something like:

size_t dice(T)(ref R rnd, T[] proportions...); 

This way, if you're passing in a pre-existing array instead of treating dice as a variadic function, you won't have to convert it.