Perfect Forwarding Multiple Arguments

How can I perfectly forward multiple arguments of different types using std::forward?

When you have a function that takes multiple arguments of different types and you want to perfectly forward them to another function, you can use std::forward() with a variadic template.

Here's an example:

#include <iostream>
#include <string>
#include <utility>

void process_data(int id,
  const std::string& name, double value) {
  std::cout
    << "ID: " << id
    << ", Name: " << name
    << ", Value: " << value << "\n";
}

template <typename... Args>
void forward_data(Args&&... args) {
  process_data(std::forward<Args>(args)...);  
}

int main() {
  int id = 42;
  std::string name = "John";
  double value = 3.14;

  forward_data(
    id, name, value);
  forward_data(
    std::move(id), name, std::move(value));
}
ID: 42, Name: John, Value: 3.14
ID: 42, Name: John, Value: 3.14

In this example, forward_data() is a variadic template function that takes any number of arguments of different types. It forwards these arguments to process_data() using std::forward<Args>(args)..., which expands the parameter pack args and applies std::forward() to each argument.

By using std::forward<Args>(args)..., each argument is perfectly forwarded to process_data(), preserving its value category (lvalue or rvalue) and const-ness.

In the main() function, forward_data() is called twice:

  1. forward_data(id, name, value): Forwards id, name, and value as lvalues.
  2. forward_data(std::move(id), name, std::move(value)): Forwards id and value as rvalues using std::move(), while name is forwarded as an lvalue.

This demonstrates how std::forward() can be used with a variadic template to perfectly forward multiple arguments of different types, preserving their value categories and const-ness.

Perfect Forwarding and std::forward

An introduction to problems that can arise when our functions forward their parameters to other functions, and how we can solve those problems with std::forward

Questions & Answers

Answers are generated by AI models and may not have been reviewed. Be mindful when running any code on your device.

Perfect Forwarding with Const References
How can I perfectly forward a const lvalue reference using std::forward?
Perfect Forwarding and Overload Resolution
How does perfect forwarding affect overload resolution when forwarding arguments to a function with multiple overloads?
Perfect Forwarding and Template Deduction
How does template argument deduction work when using perfect forwarding with std::forward?
Perfect Forwarding and Move-Only Types
How does perfect forwarding with std::forward handle move-only types?
Perfect Forwarding and Return Values
Can perfect forwarding with std::forward be used to forward return values from a function?
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