In-Reply-To: <20060921173331.GJ14139@lie.Stanford.EDU> irving@cs.stanford.edu (Geoffrey Irving) wrote (abridged):

I don't think there's any reason to overthink this. The simple scheme works:

template<class T> class vector3 { public: T x,y,z;

vector3() { assert(&z == &x+3); }

T& operator[](unsigned i) {assert(i<3);return (&x)[i];} };

It can probably even be considered standard compliant: if the assert doesn't hit, I'm pretty sure the standard guarantees that the code is correct.

You probably meant "&x+2" in the first assert. I agree if that assert passes the code probably works, but I don't think the assert is guaranteed to pass. Personally I don't think code like that belongs in Boost; Boost ought to be exemplary. I'd prefer: template<class T> class vector3 { T base[3]; public: T& operator[](unsigned i) { assert(i<3); return base[i]; } T& x() { return base[0]; } T& y() { return base[1]; } T& z() { return base[2]; } }; with no public variables. The encapsulation is worth the extra brackets. (Actually I'd rather use v.set_x(3) than v.x() = 3.) -- Dave Harris, Nottingham, UK.