Arrays

[Daniel Keep]

Olli Aalto wrote:
> Stewart Gordon wrote:
> 
>> Olli Aalto wrote:
>>
>>> Hi!
>>>
>>> I've been playing with arrays lately. Static arrays, 2/3/4 
>>> dimensional arrays and dynamic arrays.
>>>
>>> First I'd like to ask if it's safe to do this:
>>>
>>> int[] getIntArrayWithLengthOf2()
>>> {
>>>     int[] array = new int[2];
>>>     array[] = 2;
>>>     return array;
>>> }
>>>
>>> some scope
>>> {
>>>     int[2] array2 = getIntArrayWithLengthOf2();
>>> }
>>>
>>> It seem to work, but what about memory? How's it handled? Do I need 
>>> to delete it if I don't want the GC take care of it?
>>
>> <snip>
>>
>> You have declared an int[2], that is a static array, so it is 
>> allocated on the stack.  What happens is that getIntArrayWithLengthOf2 
>> allocates an array on the heap, and then its contents are copied into 
>> array2.  The array allocated on the heap becomes unreachable, and so 
>> will be picked up by the GC the next time it runs, even if control is 
>> still within some scope.  The copy in array2, OTOH, will persist until 
>> the end of the scope.
>>
>> If OTOH you declared
>>
>>     int[] array2 = getIntArrayWithLengthOf2();
>>
>> then array2 is a dynamic array.  Assignment is then by reference, and 
>> so array2 points into the memory allocated on the heap by 
>> getIntArrayWithLengthOf2.  The GC will not free the heap-allocated 
>> memory until array2 goes out of scope or is assigned something else. 
>> Even then, it will only free it if no other reachable reference to it 
>> exists.
>>
> 
> Thanks for the explanation.
> 
> I'm still wondering why I can't return a static array from a function. I 
> know it will be out of scope, but couldn't the contents be copied like 
> in the above example?
> 
> 
> O.

It's a somewhat round-about way of doing it, but you could always try 
something like this:

struct StaticArray(T, uint n)
{
     T[n] data;
}

StaticArray!(int,2) getIntArrayWithLengthOf2()
{
     StaticArray!(int,2) result;
     result.data[] = 2;
     return result;
}

I'm not 100% sure if you could use opCast to make the code a bit easier 
on the user end, or other template tricks you could apply.

Hope this helps some,

	-- Daniel