this() not executing code on structs

[Andrei Alexandrescu]

Today, structs can't write their own this(). There aren't very solid 
reasons for that except that it makes language implementation more 
difficult.

I wonder how much of a problem that could be in practice. I realized 
today that the "Counted" example - a classic C++ primer example 
featuring a struct that counts its own instances - cannot be implemented 
in D.

In C++ the counted example looks like this:

struct Counted {
    static unsigned count;
    unsigned myCount;
    Counted() { myCount = count++; }
    Counted(const Counted& rhs) { myCount = count++; }
    Counted& operator=(const Counted& rhs) {
       // no writing to myCount
       return *this;
    }
    ~Counted() {
       --count;
    }
}

In D there's no chance to write Counted because you can always create 
Counted objects without executing any code.

struct Counted {
    static uint count;
    uint myCount;
    this() { myCount = count++; }       // ERROR
    this(this) { myCount = count++; }
    ref Counted opAssign(Counted rhs) {
       // no writing to myCount
       return this;
    }
    ~this() {
       --count;
    }
}

This being a toy example, I wonder whether there are much more serious 
examples that would be impossible to implement within D.


Andrei