如何从 std::optional::value_or 返回常量引用？

Question

struct A
{
    static const bool mDefault = true;
    std::optional<bool> mValue;
    const bool& GetDefaultValue() { return mDefault; }
    const bool& GetValue() { return mValue.value_or( GetDefaultValue() ); }
};

int main(int argc, char *argv[])
{
    std::cout << A().GetValue() << std::endl;
}

When compile that code we obtain a returning reference to temporary warning cause value_or return by value. There is a way to return a const reference?

Answer 1

value_or returns by value. It's already a copy. You'll have to do it yourself.

const bool& GetValue() { return mValue ? mValue.value() : mDefault; }