hashed array?

[Don]

On 14.11.2012 20:15, Rainer Schuetze wrote:
>
> On 11/14/2012 7:20 PM, Dmitry Olshansky wrote:
>> 11/14/2012 9:44 PM, Andrei Alexandrescu пишет:
>>>
>>> This is new! What does this mean?
>>>
>>
>> I'm sure it is nothing new. Basically AA is a reference type but it is
>> auto-magically created on the first insertion. This is called magic null
>> behavior.
>>
>> void foo(int[int] aa){
>> //aa here is null
>> aa[1] = 1;
>> //now the local aa points to a new hash-map
>> }
>>
>> void main(){
>> int[int] map;
>> foo(map);
>> //map in this scope is still null
>> assert(1 in map); // fails
>> }
>>
>>
>> I'm in favor of implicitly allocating an AA on definition that'll make
>> it a proper reference type.
>>
>
> I don't like the "magic null behaviour", but I see issues with this
> straight forward implementation: how can you define a statically
> initialized struct value (including init) that contains an associative
> array? It will have to run a default constructor to allocate the AA root
> object, introducing something like the often rejected user-defined
> default constructor for structs.

It doesn't need to allocate any keys or values. It just needs to 
allocate whatever structure it needs to keep track of how many items it 
has. As if you added an element, and then removed it.