https://svn.boost.org/trac10/ticket/9044 <p> Some operators, like the ones for comparison &amp; equality, generally don't require mutating operations for their work. That means those functions can be <code>constexpr</code> if they use a literal operand type and the base operators are themselves <code>constexpr</code>. </p> en-us /htdocs/site/boost.png https://svn.boost.org/trac10/ticket/9044 Trac 1.4.3