----- Original Message ----- From: "Henning Basold" <h.basold@googlemail.com> To: <boost@lists.boost.org> Sent: Sunday, August 22, 2010 5:49 PM Subject: [boost] Interest in specialized types
Hello,
in http://permalink.gmane.org/gmane.comp.lib.boost.devel/207794 Robert Ramey talked about wrapping some POD to increase type safety. Some time ago I used something similar to ensure that misuse of values can be found by the compiler.
So I think that is something that can be generalized. The concept is to wrap a type into a class and restrict the interface. This ensures that values from one context (e.g. an id) can't be used in another context (e.g. adding of number or as an id for other objects).
Attached is a very simple implementation where the needed concepts can be specified as parameter. To distinguish for example between different id types also a tag type can be specified.
Do you think this might be a useful utility? Or is there something similar already available? I've searched the vault but did not find anything.
Hi, I'm currently working on Boost.Opaque http://svn.boost.org/svn/boost/sandbox/opaque/ (Not yet on the Vault) which tries to implement strong typedefs for fundamental types. It is based on "Progress toward Opaque Typedefs for C++0X" http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2005/n1891.pdf which was not accepted for inclusion on C++0x. // Cartesian 3D coordinate types BOOST_OPAQUE_PUBLIC_TYPEDEF(double, X); BOOST_OPAQUE_PUBLIC_TYPEDEF(double, Y); BOOST_OPAQUE_PUBLIC_TYPEDEF(double, Z); // polar 3D coordinate types BOOST_OPAQUE_PUBLIC_TYPEDEF(double, Rho); BOOST_OPAQUE_PUBLIC_TYPEDEF(double, Theta); BOOST_OPAQUE_PUBLIC_TYPEDEF(double, Phi); class PhysicsVector { public: PhysicsVector(X, Y, Z); PhysicsVector(Rho, Theta, Phi); ... }; // PhysicsVector The approach I have taken doesn't allows, as yours, to restrict the interface but just to allow or not the implicit conversion between the opaque/strong-typed type and the underlying type. I recognize that the ability to restrict the interface is more general, but I'll need some concrete use cases for which restricting the interface is absolutlely needed. Best, Vicente