struct constructor co nfusion

[Spacen Jasset via Digitalmars-d-learn]

On Friday, 6 November 2015 at 17:50:17 UTC, Atila Neves wrote:
> On Friday, 6 November 2015 at 17:34:29 UTC, Spacen Jasset wrote:
>> Hello,
>>
>> I have read various things about struct constructors, 
>> specifically 0 argument constructors, and using opCall and 
>> @disable this(); which no longer seems to work.
>>
>> What I am after I think is the behavior of C++'s structs on 
>> the stack, namely for some or all of these uses at a given 
>> time:
>>
>>
>> 1. Allocation on the stack
>> 2. Value type semantics
>> 3. RAII (combined with (1) often)
>
> This is common in D as well. The difference to C++ is 
> 0-argument struct constructors to do extra work to satisfy 
> invariants.
>
>> Is it the case that a struct should now be used with a factory 
>> method? Does this also mean that the struct destructor must be
>
> It's the easiest way to emulate C++'s 0-argument struct 
> constructors.
>
>> made to work when .init is called instead of the factory 
>> method?
>
> If the factory method isn't called, then yes, the destructor 
> shouldn't blow up just because all the struct members are 
> T.init.
>
>> This idiom is inconsistent with struct constructors that do 
>> have one or more arguments, and I think that this question is 
>> likely to arise time immemorial from others who are not 
>> expecting this particular inconstancy.
>
>
> How is it inconsistent? Nobody stops me from doing this:
>
> struct Struct {
>     void* ptr = cast(void*)5;
>     this(int size) {
>         ptr = malloc(size);
>     }
>
>     ~this() {
>         free(ptr);
>     }
>
> }
>
> void main() {
>     auto ok = Struct(10);
>     //auto oops = Struct.init;
> }
>
> Atila

What I mean is that:

this(int a, int b) {} is allowed

Whereas:
this() {} isn't allowed. I see why that is the case now, but it 
seems inconsistent to me, and I think each new person that comes 
to D is going to wonder about this.


Also, I had to add a dummy private constructor to make my structs 
'createable', or is there another way?

e.g.

struct Texture
{
     @disable this();
     static Texture create()
     {
	return Texture(0);
     }
	
...

private:
	this(int)
	{
		glGenTextures(1, &textureId_);
		enforce(0 != textureId_);
	}

	GLuint textureId_;
}