On Mon, 2008-03-31 at 15:22 +0100, Giovanni Piero Deretta wrote:
but in general it might reopen the problem of deferred typechecking of template parameters. Are constrained template template parameters legal?
Yes.
i.e.:
// Takes a constrained template: template<template<Value> class S> // is this syntax even legal? struct foo {};
// A constrained template template<Regular Value> struct vector {};
foo<vector> f; // OK?
Yes, this is fine, assuming that the template template parameter S was meant to be written as: template<Regular> class S You could also have more constraints on the template argument, e.g., template<Regular Value> requires LessThanComparable<Value> struct set; foo<set> f2; // okay
[ If it is not legal, I guess you could fake it with concept achetypes and some kind of rebind trick.]
Ick.
Not useful for metaprogramming, but for more mundane things, you might not want to lose the benefits of concept typechecking.
It might be useful for metaprogramming; I don't actually know. Some metaprogramming is likely to change when using concepts, but we're doing our best not to hurt metaprogramming in the process of adding concepts. - Doug