Summary - Modern C++
- C++ course
- Advanced
- Lesson 6/83
- 5 min
Combine structured bindings, concepts and ranges to write a data pipeline.
Summary - Modern C++
In this group you met five key tools of C++17 and C++20: safe returns with std::optional, multi-value unpacking with structured bindings, compile-time branches with if constexpr, template constraints with concepts and composable views with ranges.
Together these tools let you write safer, more readable and faster code. Now you will combine what you learned in a small task.
Practice Summary with twice + binding
Write template <typename T> auto twice(T x); in the body use if constexpr to return x * 2 when std::is_integral_v<T> is true, otherwise x. In main bind with auto [mn, mx] = std::pair{twice(5), twice(7)}; and print mn + mx via std::cout.
Starter code
#include <iostream>
#include <type_traits>
#include <utility>
// Write the twice template
int main() {
// Bind and print the sum
return 0;
}Sample solution
#include <iostream>
#include <type_traits>
#include <utility>
template <typename T>
auto twice(T x) {
if constexpr (std::is_integral_v<T>) return x * 2;
return x;
}
int main() {
auto [mn, mx] = std::pair{twice(5), twice(7)};
std::cout << mn + mx;
return 0;
}Expected output
24
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 Which tool constrains template parameters?
- std::optional
- concepts Correct answer
- ranges
- structured bindings
Explanation: concepts constrain templates through a requires clause.
2 Match the tool to its purpose
| Term | Meaning |
|---|---|
std::optional |
Safe return |
structured bindings |
Multi unpack |
if constexpr |
Compile-time branch |
ranges |
Composable view |
3 Complete the if constexpr line
template <typename T>
auto twice(T x) {
____ (std::is_integral_v<T>) return x * 2;
return x;
}template <typename T>
auto twice(T x) {
if constexpr (std::is_integral_v<T>) return x * 2;
return x;
}Explanation: if constexpr is a compile-time branch.