Michael Fawcett wrote:
On Mon, Nov 30, 2009 at 7:25 AM, Vicente Botet Escriba <vicente.botet@wanadoo.fr> wrote:
"In a nutshell, `common_type` is a trait that takes 1 or more types, and returns a type which all of the types will convert to. The default definition demands this conversion be implicit. However the trait can be specialized for user-defined types which want to limit their inter-type conversions to explicit, and yet still want to interoperate with the `common_type` facility.
Example:
template <class T, class U> typename common_type<complex<T>, complex<U> >::type operator+(complex<T>, complex<U>);
In the above example, "mixed-mode" complex arithmetic is allowed. The return type is described by `common_type`. For example the resulting type of adding a `complex<int>` and `complex<double>` might be a `complex<double>`."
I've needed this feature many times. Can you explain the pros/cons of common_type against Boost.Typeof?
Thanks,
--Michael Fawcett _______________________________________________ Unsubscribe & other changes: http://lists.boost.org/mailman/listinfo.cgi/boost
Hi, Happy to hear you could find a use for this class. Even if in a first look they sound to be close, common_type and typeof have different purposes. You use typeof to get the type of an expression, while you use common_type to set explicitly the type returned of a template function. Both are complementary. For example with the preceding declaration and the needed Typeof registrations, you can do complex<int> ic; complex<double> id; BOOST_AUTO(icd, ic+id); Surely others would give a better explanation, Regards, Vicente -- View this message in context: http://old.nabble.com/-chrono--type_traits-common_type-and-integer-ratio-tp2... Sent from the Boost - Dev mailing list archive at Nabble.com.