Message du 03/05/11 20:53 De : "Marsh Ray" A : boost@lists.boost.org Copie à : "Jeff Flinn" Objet : Re: [boost] [review] string convert
On 05/03/2011 11:41 AM, Jeff Flinn wrote:
I personally don't have those reservations and the applicability of Make. Even more concise with perhaps less preconceptions might be:
as(s, 123);
Just a data point: I've been using 'obj.as' as my own convention for a few years now and I like it.
It was a little easier on a "lenient" compiler where I started using it:
struct mytype { // Unimplemented general template. template U as() const { BOOST_MPL_ASSERT_MSG(false, NO_CONVERSION_TO, (U)); }
// specializations define the types we support "conversions" to: template <> std::string as() const {return this->to_string_imp(); } template <> std::wstring as() const {return this->to_wstring_imp();} ...possibly more... ... };
template T f() { mytype m(...); return m.as(); }
Just tried it again the other day with a class template on a more conforming compiler (which required member specializations at namespace scope). It was a lot more overhead code to make it work.
If this library could help me define explicit conversions "as" member templates with a sane amount of boilerplate again, I'd be a fan.
explicit conversion are supported by C++11. Boost.Conversion let you already define explicit conversion but not as member templates. You will need to overload the convert_to function for the Source and target types as follows: Target convert_to(const Source& from, boost::dummy::type_tag const&) { // your specific code } Once this is done you could write your function f() as ***** Sorry I have replaced angle brackets by (* and *) ********** template (*class T*) T f() { mytype m(...); return boost::convert_to(*T*)(m); } Best, Vicente