Is that a bug or I misunderstood it?

[jojogh]

I made a small test on the yap, I made two simple plus expression templates under minial template example case. One is directly in a main function, and another is in a struct operator. As we expected, both results should be the small. In fact, it is not, if called the struct operator, the result is not 42, but a wired number. Is that a bug or I misunderstood it, and made wrong setting? I really looking forward to your replys, many thanks! @tzlaine @danieljames

#include <boost/yap/algorithm.hpp>

#include <array>
#include <iostream>

//[ minimal_template
template <boost::yap::expr_kind Kind, typename Tuple>
struct minimal_expr
{
    static const boost::yap::expr_kind kind = Kind;

    Tuple elements;
};
//]

struct eval {
    auto operator() (const double a, const double b) const {
        const auto lhs_w = boost::yap::make_terminal<minimal_expr>(std::move(a));
        const auto rhs_w = boost::yap::make_terminal<minimal_expr>(std::move(b));
        const auto expr = boost::yap::make_expression<
            minimal_expr, boost::yap::expr_kind::plus
        >(lhs_w, rhs_w);

        return expr;
    }
};

int main()
{
    //[ minimal_template_manual_construction
    auto left = boost::yap::make_terminal<minimal_expr>(1);
    auto right = boost::yap::make_terminal<minimal_expr>(41);

    auto expr = boost::yap::make_expression<
        minimal_expr,
        boost::yap::expr_kind::plus >(left, right);
    //]

    //[ minimal_template_evaluation
    auto result = boost::yap::evaluate(expr);

    std::cout << result << "\n"; // prints "42"
//]
    eval Eval;
    auto ex = Eval(1, 41);
    auto res = boost::yap::evaluate(ex);
    std::cout << res << "\n"; // prints "42"
    system("pause");
    return 0;
}

[tzlaine]

In eval::operator(), return expr; returns an expression whose subexpressions are lvalue references to locals. You have a dangling reference problem.

[jojogh]

many thanks

Zach Laine notifications@github.com 于2020年4月9日周四 上午7:21写道：

Closed #102 https://github.com/boostorg/yap/issues/102.

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