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
This is an older version of Boost and was released in 2017. The current version is 1.90.0.
static int const cols = /*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 columns of a user-defined matrix type.