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
