Boost C++ Libraries

...one of the most highly regarded and expertly designed C++ library projects in the world. — Herb Sutter and Andrei Alexandrescu, C++ Coding Standards

QVM: Quaternions, Vectors, Matrices

namespace boost
{
    namespace qvm
    {
        -unspecified-return-type- transposed();
    }
}

The expression transposed(m) returns a mutable view proxy that transposes the matrix m.