## When Should I Use std::forward in C Function Templates?

Understanding the Use Cases of std::forward in C

C 0x introduces the std::forward function, a valuable tool for forwarding arguments in function templates. When using std::forward, it's important to consider when and how it should be employed.

When to Use std::forward

std::forward is primarily used when passing arguments to another function template:

<code class="cpp">template<class t>
void foo(T&& arg)
{
  bar(std::forward<t>(arg));
}</t></class></code>

In this example, std::forward allows foo to forward the argument arg to bar with the correct type and reference qualification. Without std::forward, the argument would be passed as a copy, potentially leading to unnecessary operations.

Parameter Declarations with &&

In the foo function above, the parameter declaration uses &&. This is not a requirement for using std::forward, but it can provide some advantages. By using &&, the function can accept both rvalues and lvalues, even if it is declared with an rvalue reference.

Forwarding in Multiple Argument Lists

In cases with multiple argument lists, std::forward can be used to forward arguments individually:

<code class="cpp">template<int val typename... params>
void doSomething(Params... args) {
  doSomethingElse<val params...>(args...);
}</val></int></code>

In this case, using && in the parameter declaration is preferred, as it allows the function to accept any type of argument. The arguments are then forwarded to doSomethingElse using std::forward:

<code class="cpp">doSomethingElse<val params...>(std::forward<params>(args)...);
}</params></val></code>

Multiple Forwarding

Forwarding the same argument to multiple functions raises concerns about moving and making the memory invalid. Therefore, it's generally not advisable to use std::forward multiple times for the same argument.

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