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

mat_traits<Matrix>::rows

static int const rows = /*user-defined*/;

This member of user-defined (partial) specializations of the mat_traits template must be a compile-time integer constant greater than zero that defines the number of rows of a user-defined matrix type.