Summary - Concepts
- C++ course
- Advanced
- Lesson 66/83
- 5 min
Combine concept, requires and standard concepts to write a generic algorithm.
Summary - Concepts
In this group you learned concept, requires, standard concepts, compound requirement and concept overloading.
Concepts name template constraints; the requires expression does compile-time expression checks; std::integral and std::floating_point are ready-made concepts; compound requirements also check the return type and the noexcept condition; concept overloading dispatches type-based overloads at compile time.
Now you will write a generic accumulate algorithm that combines these four. It will be a safe and readable template built with concepts.
Practice Write a generic accumulate
Write the template function template<std::integral T> T accumulate(const std::vector<T>& data). Its body sums the data and returns it. In main create std::vector<int> data{1, 2, 3, 4}; and print the result of accumulate(data) with std::cout.
Starter code
#include <iostream>
#include <vector>
#include <concepts>
// Write the accumulate template function here
int main() {
// Create data, call it and print
return 0;
}Sample solution
#include <iostream>
#include <vector>
#include <concepts>
template<std::integral T>
T accumulate(const std::vector<T>& data) {
T sum = T{0};
for (auto x : data) {
sum += x;
}
return sum;
}
int main() {
std::vector<int> data{1, 2, 3, 4};
std::cout << accumulate(data);
return 0;
}Expected output
10
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 Which keyword starts a concept definition?
- template
- static_assert
- concept Correct answer
- requires
Explanation: The concept keyword starts a concept definition.
2 Match each idea to its description
| Term | Meaning |
|---|---|
concept |
Named constraint |
requires |
Expression check |
std::integral |
Ready integral concept |
compound |
Return type check |
3 the accumulate call
std::cout << ____(data.begin(), data.end());std::cout << accumulate(data.begin(), data.end());Explanation: The accumulate function sums an iterator range.