Struct default constructor - need some kind of solution for C++ interop

[John Colvin via Digitalmars-d]

On Tuesday, 6 September 2016 at 13:44:37 UTC, Ethan Watson wrote:
> So now I'm in a bind. This is one struct I need to construct 
> uniquely every time. And I also need to keep the usability up 
> to not require calling some other function since this is 
> matching a C++ class's functionality, including its ability to 
> instantiate anywhere.
>
> Suggestions?

I know you don't like the explicit function-calling way, but I 
think it is actually quite good, if you consider what the 
compiler does and doesn't allow

e.g.

struct S
{
	int a;
	@disable this();
	private this(int a) // just for ease of use in `create`
	{
		this.a = a;
	}
	static create() // could be free function instead
	{
		auto x = runtimeGetMySuperImportantUniqueValue();
		return(S(x));
	}
}

struct S1
{
	S s; // fine despite @disable this()

	// blah blah other state
	
	this(int argForOtherState)
	{
		// if you comment this out, it doesn't compile,
		// the compiler enforces initialisation for s
		// because of @disable this()
		s = S.create();
		
		// blah blah other construction
	}
}

void main()
{
//	S1 s1; // doesn't compile, would bypass initialisation of s1.s
	S1 s1 = S1(-1); // OK
}