Inserting to associative array do not return a lvalue.

[Bill Baxter]

Steven Schveighoffer wrote:
> "Bill Baxter" wrote
>> BCS wrote:
>>> Reply to Yang,
>>>
> 
> Technically, the extra lookup isn't very costly.  Most likely you add keys 
> rarely.  To make the code more optimized, you would do something like:
> 
> int *r = null;
> if(!(r = 1 in a))
> {
>     a[1] = 0;
>     r = 1 in a;
> }
> *r = 2;
> (*r)++;
> 
> This allows you to avoid the extra lookup (actually extra 2 lookups) if the 
> node already exists, which should be the more common case.  If you analyze 
> it in big-O notation, the extra-lookup factor is really only a constant, and 
> so the complexity is the same.
> 
> However, we already have properties on AA's that are built into the 
> language.  Would it not make sense to do this as a property? e.g.:
> 
> int *r = a.setval(1, 2);
> (*r)++;
> 
> Due to the way functions on arrays can be used as properties, you could even 
> have:
> 
> int *setval(int[int] arr, int key, int val)
> {
>   int *r = key in arr;
>   if(!r) // triple lookup only on first call to setval
>   {
>      arr[key] = val;
>      r = key in arr;
>   }
>   else
>     *r = val;
>   return r;
> }
> 
> This can be done without augmenting the language spec, although it still has 
> the triple lookup cost on the first call which could be avoided if it was 
> done in the language itself.  I'm sure someone out there can templatize this 
> :)

I'd also like to have Python's pop,popitem,get,setdefault, and update 
functions built-in.  Or at least defined in a std.something.

--bb