Empty collections allocate a surprising amount

[andrewhickman]

In the standard library, the only collection that allocates when you call new() is VecDeque, which will allocate space for 7 elements.

By comparison, the collections in this library allocate a lot more. Using an element type of u64 for testing:

• HashSet (and HashMap) will allocate a small amount for the hasher (which is typically a 0-size or Copy type) and 536 bytes of space
• OrdSet allocates 1080 bytes
• Vector allocates 544 bytes

I'm not sure if this is easily fixable without a performance penalty but it would be nice to not allocate at all.

[bodil]

It would be nice, but I share your concern about a performance penalty - I'd rather waste memory than cycles, tbh. It might be a negligible hit, though - I'll try it and see.