Re: 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
}