Method assign_expr

ext/include/boost/optional/optional.hpp:371–376

#ifndef BOOST_OPTIONAL_DETAIL_NO_RVALUE_REFERENCES
    template<class Expr, class ExprPtr>
    void assign_expr ( Expr&& expr, ExprPtr const* tag )
    {
      if (is_initialized())
        assign_expr_to_initialized(boost::forward<Expr>(expr),tag);
      else construct(boost::forward<Expr>(expr),tag);
    }
#else
    template<class Expr>
    void assign_expr ( Expr const& expr, Expr const* tag )