C++
Concept overloading
Learn function overloading with concepts.
What is concept overloading?
Concept overloading is defining the same template function name several times with different concept constraints. At a call site the compiler picks the best overload based on which concept the type satisfies.
Example: a print function can be written separately for integral and floating_point types. template<std::integral T> void print(T v) and template<std::floating_point T> void print(T v). print(3) calls the integral version, print(2.5) calls the floating_point version. Type-based behaviour is then dispatched at compile time.
More specialised concept
In concept overloading, a more specialised concept is preferred over a more general one. std::integral is more general; std::signed_integral is more specialised.
Example: if both std::integral and std::signed_integral versions exist, print(-3) goes to the signed version. Because int is both integral and signed_integral; signed_integral is more specific. The compiler makes this choice with partial ordering. The correct version is then picked without ambiguity.
Exercise Write integral and floating_point print
Write two print overloads: first template<std::integral T> void print(T v) with body std::cout << "i:" << v;; second template<std::floating_point T> void print(T v) with body std::cout << "f:" << v;. In main call print(3).
Show example solution
#include <iostream>
#include <concepts>
template<std::integral T>
void print(T v) {
std::cout << "i:" << v;
}
template<std::floating_point T>
void print(T v) {
std::cout << "f:" << v;
}
int main() {
print(3);
return 0;
}
Test yourself
-
How is the overload chosen?
- By which concept the type satisfies
- It is chosen randomly
- The type is queried at runtime
- By the order of function definitions
Show answer
By which concept the type satisfies — The compiler checks which concept the call type satisfies and picks the most specialised version.
-
Match the call to the type
- print(3)
- int call
- print(2.5)
- double call
- print('a')
- char call
- print(3.14f)
- float call
-
Floating-point constraint
template<____ T> void print(T v) { std::cout << v; }
Show answer
template<std::floating_point T> void print(T v) { std::cout << v; }
Next lesson: Summary - Concepts
