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I am wondering about forwarding: The standard implements std::forward basically with two overloads:

  1. To forward lvalues as lvalues/rvalues (dep. of T)
template<typename T>
T&& forward(lvalue_Reference v){ 
    return static_cast<T&&>(v); 
};
  1. To forward rvalues as rvalues
template<typename T>
T&& forward(rvalue_Reference v){  
    // static-assert: T is not an lvalue-Reference
    return static_cast<T&&>(v); 
};

First case comes to play when

template<typename T>
void foo(T&& a) { doSomething(std::forward<T>(a)); /* a is lvalue -> matches 1. overload */ }

The second case makes sense, but what is an example of triggering it?

Nicol Bolas
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Gabriel
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  • Well, totally depends on the use case :-P ... – πάντα ῥεῖ Aug 07 '19 at 17:25
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    The second case is a universal reference and it forwards both: lvalues as lvalues, rvalues as rvalues. – Sam Varshavchik Aug 07 '19 at 17:27
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    @SamVarshavchik: The second argument is actually: `rvalue_Reference := typename std::remove_reference_t&&` and is not a forwarding-reference (universal reference) as far as I know... so your statement is incorrect. – Gabriel Aug 07 '19 at 17:34
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    [Possible dupe](https://stackoverflow.com/questions/56416819/why-forwarding-return-value-is-needed/56417076#56417076) (Similar question, but I wrote an answer that answers this question too) – Artyer Aug 07 '19 at 18:13

1 Answers1

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I believe this is a duplicate of:

What is the purpose of std::forward()'s rvalue reference overload?

Please also read the included paper:

http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2009/n2951.html

Okan Barut
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