best idiom for insert if not present; else use value in assoc array

[Dan]

On Thursday, 7 February 2013 at 20:46:31 UTC, Andrej Mitrovic 
wrote:

> auto ref set(Hash, Key, Val)(Hash hash, Key key, Val val)
>     if (isAssociativeArray!Hash &&
>         is(Key : KeyType!Hash) &&
>         is(Val : ValueType!Hash))
> {
>     if (auto res = key in hash)
>     {
>         return res;
>     }
>     else
>     {
>         hash[key] = val;
>         return key in hash;
>     }
> }

Definitely a convenient function, but I think what Jonathan and 
bearophile suggested was something more like:

auto ptrToValue = hash.insertDefaultOrFind(key, init)
*ptrToValue += additional;

and then on the first insert for a given key the hash is computed 
just once. I believe this would have to be done at the level of 
AssociativeArray and can not be done as a helper function, since 
this set helper is still doing 3 hashes/lookups.

Thanks
Dan