CODEWITHSUNDEEP
c++c++11referencervalue-referencelvalue
Shepard
Shepard

Reputation: 811

C++ reference for both LValue and Rvalue without type deduction

I was reading a good tutorial on lvalue/rvalue references. If I've understood correctly when there is type deduction something like T&& can accept both an lvalue and an rvalue.

But is there a way to achieve that without a generic class? I'd like to avoid duplicating all my methods for accepting both lvalues and rvalues. And of course avoid passing big objects by value.

Upvotes: 0

Views: 878

Answers (2)

Philipp Claßen
Philipp Claßen

Reputation: 43979

If the function that you implement does not need rvalue semantic, then you can simply pass the argument by reference or by constant reference.

However, if you can take advantage of rvalues and do not want to duplicate your code, you can pass by value and move the result. That should be almost as efficient and can be more maintainable than code duplication or an implementation with universal references.

This answer shows the technique: Should all/most setter functions in C++11 be written as function templates accepting universal references?

// copy, then move
void set_a(A a_) { a = std::move(a_); }

Upvotes: 2

Jarod42
Jarod42

Reputation: 217293

r-value references are mostly use in move-constructor and move assignment.

For regular method, you may stick with one reference type only:

  • For read only parameter (without copy), const reference is enough.

  • if you have to do a copy, you may take your argument by value and use std::move:

Example:

class Test
{
public:

    void displayString(const std::string& s) const { std::cout << s << m_s; }

    void setString(std::string s) { m_s = std::move(s); }

private:
    std::string m_s;
};

Upvotes: 2

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