Arrays of variants, C++ vs D

[Steven Schveighoffer]

On 6/17/21 4:15 PM, H. S. Teoh wrote:
> On Thu, Jun 17, 2021 at 07:44:31PM +0000, JN via Digitalmars-d-learn wrote:
> [...]
>>      Foo[int] foos = [
>>          0: Foo("abc"),
>>          1: Foo(5)
>>      ];
>> }
>> ```
>>
>> Why does D need the explicit declarations whereas C++ can infer it?
> 
> Because D does not support implicit construction. The array literal is
> parsed as-is, meaning string[int] is inferred rather than Foo[int]. So
> the initialization fails because of a type mismatch.

Implicit construction is supported:

struct Foo
{
    int x;
    this(int y) { x = y; }
}

Foo f = 5; // ok implicit construction

What is happening here though is that the construction is being done as 
an AA literal. This works for *some* types, but not all.

e.g.:

Foo[int] f = [5 : 5]; // error
double[int] f = [5 : 5]; // ok

It really should work IMO.

-Steve