# QVM: Quaternions, Vectors, Matrices

### deduce_quat2

#include <boost/qvm/deduce_quat.hpp>

    namespace boost
    {
        namespace qvm
        {
            template <class A,class B>
            struct deduce_quat2
            {
                typedef /*unspecified*/ type;
            };
        }
    }

#### Assumptions:

- Both scalar<A>::type and scalar<B>::type are well defined
- is_quat<A>::value || is_quat<B>::value is true

#### Requirements:

- is_quat<deduce_quat2<A,B>::type>::value must be true
- deduce_quat2<A,B>::type must be copyable

This template is used by Boost QVM whenever it needs to deduce a quaternion type from the types of two user-supplied function parameters. The returned type must have accessible copy constructor (the A and B types themselves could be non-copyable, and either one of them may not be a quaternion type.)

The main template definition returns an unspecified quaternion type with scalar_type obtained by deduce_scalar<A,B>::type, except if A and B are the same quaternion type Q, in which case Q is returned, which is only suitable for copyable types. Boost QVM also defines (partial) specializations for the non-copyable quaternion types it produces. Users can define other (partial) specializations for their own types.

A typical use of the deduce_quat2 template is for specifying the preferred quaternion type to be returned by the generic function template overloads in Boost QVM depending on the type of their arguments.

See also: boost/qvm/deduce_quat.hpp | boost/qvm/quat_traits_array.hpp | operator*(quat,quat) | operator+(quat,quat) | operator-(quat,quat) | slerp