Auto recursive function

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On Wednesday, 11 January 2017 at 19:23:10 UTC, Razvan Nitu wrote:
> Hi,
>
> I am currently trying to create a function 
> makeMultidimensionalArray which allocates memory for a 
> multidimensional array. It is very similar with [1],
> the difference being that it is uninitialized. Here is the code:
>
> auto makeMultidimensionalArray(T, Allocator)(auto ref Allocator 
> alloc, size_t[] lengths)
> {
>     if (lengths.length == 1)
>     {
>         return makeArray!T(alloc, lengths[0]);
>     }
>     else
>     {
>         alias E = typeof(makeMultidimensionalArray!T(alloc, 
> lengths[1..$]));
>         auto ret = makeArray!E(alloc, lengths[0]);
>         foreach (ref e; ret)
>             e = makeMultidimensionalArray!T(alloc, 
> lengths[1..$]);
>         return ret;
>     }
> }
>
> The lengths[] specifies the lengths for each dimension. The 
> problem with this code is that auto is going to be evaluated to 
> T[] for the first time and when it
> recurs, creating T[][] I get the error "mismatched function 
> return type inference of T[][] and T[]". Is there a way to 
> surpass that? I saw that in [1]
> the recursive call is done by prefixing the function name with 
> a '.'; I tried that but it doesn't work. I must be missing 
> something, any ideas?
>
> Thanks,
> RazvanN
>
> [1] 
> https://github.com/dlang/phobos/blob/master/std/experimental/ndslice/slice.d#L834


If you change the return type to a void* your code basically 
works.


void* makeMultidimensionalArray(T, Allocator)(auto ref Allocator 
alloc, size_t[] lengths)
{
     if (lengths.length == 1)
     {
		int x = 0x01FEEF01;
         return cast(void*)makeArray!T(alloc, lengths[0], x);
     }
     else
     {
         alias E = typeof(makeMultidimensionalArray!T(alloc, 
lengths[1..$]));

         auto ret = makeArray!E(alloc, lengths[0]);
         foreach (ref e; ret)
             e = makeMultidimensionalArray!T(alloc, lengths[1..$]);
         return cast(void*)ret;
     }
}

The problem is that then you need to cast back and that 
essentially results in the original problem. Can be done but 
probably gonna have to use string mixins.