Auto recursive function

[Ali Çehreli via Digitalmars-d-learn]

On 01/11/2017 11:30 AM, Stefan Koch wrote:
> 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:
>>
>> [...]
>
> I believe you should not do this with recursion.
> Because that'll instantiate the template multiple times with different
> types.
> What is wrong with using ndslice here ?
>

Agreed but the question is still valid. I had similar cases before where 
std.range.choose looked like a solution but did not work. Here's my 
current attempt, which fails:

import std.stdio;
import std.experimental.allocator.gc_allocator;
import std.experimental.allocator;

auto one(T, Allocator)(auto ref Allocator alloc, size_t length) {
     return makeArray!T(alloc, length);
}

auto two(T, Allocator)(auto ref Allocator alloc, size_t[] lengths) {


// Error: forward reference to inferred return type of function call 
'makeMultidimensionalArray!int(alloc, lengths[1..__dollar])'


     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;
}

auto makeMultidimensionalArray(T, Allocator)(auto ref Allocator alloc, 
size_t[] lengths)
{
     import std.range: choose;

     return choose(lengths.length == 1, one!T(alloc, lengths[0]), 
two!T(alloc, lengths));
}

void main() {
     writeln(makeMultidimensionalArray!int(GCAllocator.instance, [3, 4]));
}

Ali