Method at

extern/boost/boost/array.hpp:126–126

at() with range check

        // at() with range check
        reference                           at(size_type i)       { return rangecheck(i), elems[i]; }
        /*BOOST_CONSTEXPR*/ const_reference at(size_type i) const { return rangecheck(i), elems[i]; }
    
        // front() and back()