toHash => pure, nothrow, const, @safe

[bearophile]

Walter:

> toHash, opEquals, and opCmp as struct members be automatically 
> annotated with pure, nothrow, and @safe (if not already marked 
> as @trusted).

I have read the other answers of this thread, and I don't like 
some of them.

In this case I think this programmer convenience doesn't justify 
adding one more special case to D purity. So for me it's a -1.

Bye,
bearophile