Return Value Optimization and const getters for data members

Asked Mar 08 '16 at 11:42

Active Mar 08 '16 at 11:42

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I understand that RVO enables copy elision of, amongst others, temporaries and local variables, but what about data members ?

To focus the question, which of the following three options is the best way to write a const getter for a data member (given RVO and C++11)?

class Widget { /* some large user-defined class */ };

class C
{
public:
    const Widget& getWidget1() const { return w; }
    const Widget getWidget2() const { return w; }
    Widget getWidget3() const { return w; }

private:
    Widget w;
};

asked Mar 08 '16 at 11:42

mr_T

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Use `const Widget& getWidget1() const { return w; }`. I can see many situations where a copy will be problematic. – πάντα ῥεῖ Mar 08 '16 at 11:44
`const Widget getWidget2() const` is bad, the `const` in front of the return value inhibits move semantics – TemplateRex Mar 08 '16 at 11:45
@πάνταῥεῖ what about lifetimes issues with `C{}.getWidget1()`? – TemplateRex Mar 08 '16 at 11:46
@TemplateRex Fair point. Depends on the actual use case though. – πάντα ῥεῖ Mar 08 '16 at 11:48
`const Widget& getWidget() const { return w; }` but `Widget takeWidget() { return std::move(w); }` – Jarod42 Mar 08 '16 at 11:53
@Jarod42 or use ref-qualifiers: `const Widget& getWidget() const &` – TemplateRex Mar 08 '16 at 11:55

Return Value Optimization and const getters for data members

0 Answers0