Why does this not compile?

[Steven Schveighoffer]

On 3/6/18 7:44 AM, Shachar Shemesh wrote:
> On 06/03/18 14:00, Steven Schveighoffer wrote:
>> On 3/6/18 6:21 AM, Simen Kjærås wrote:
>>> On Tuesday, 6 March 2018 at 10:03:54 UTC, Shachar Shemesh wrote:
>>>> void main() {
>>>>     struct S {
>>>>         uint value;
>>>>
>>>>         ~this() {
>>>>         }
>>>>     }
>>>>
>>>>     const S a = S(12);
>>>>     S b = a;
>>>> }
>>>>
>>>> test.d(10): Error: cannot implicitly convert expression a of type 
>>>> const(S) to S
>>>
>>> Looks like a bug to me - please file one in bugzilla.
>>
>> Nope. It's not a bug. S contains a pointer, namely the context pointer 
>> for main.
>>
>> https://dlang.org/spec/struct.html#nested
> 
> Which does not explain why my code compiles if I remove the destructor.

If the struct is POD, there is no need to include the context pointer.

void main()
{
    struct POD { int x; }
    pragma(msg, POD.sizeof); // 4
    struct Nested { int x; void someMember() {} }
    pragma(msg, Nested.sizeof); // 16
}

-Steve