boost::yap::cond
// In header: <boost/yap/algorithm.hpp> template<typename Expr> decltype(auto) constexpr cond(Expr && expr);
Returns the condition expression in an if_else expression.
Equivalent to get(expr, 0_c).
get(expr, 0_c)
cond() is only valid if Expr is an expr_kind::if_else expression.
cond()
expr_kind::if_else