Requiring Multiple Member Functions

You can use a combination of requires expressions within a concept to specify that a class should have multiple member functions with specific signatures. Here's an example:

1#include <concepts>
2#include <string>
3
4template <typename T>
5concept Serializable = requires(T x) {
6  { x.Serialize() }
7    -> std::same_as<std::string>;
8  { x.Deserialize(std::declval<std::string>()) }
9    -> std::same_as<void>;
10};
11
12class DataRecord {
13public:
14  std::string Serialize() {
15    return "Serialized data";
16  }
17
18  void Deserialize(const std::string& data) {
19    // Deserialize logic
20  }
21};
22
23// Passes
24static_assert(Serializable<DataRecord>);

In this example, the Serializable concept requires a type T to have two member functions:

1. Serialize(): Takes no arguments and returns a std::string.
2. Deserialize(std::string): Takes a std::string argument and returns void.

The requires expressions within the concept check for the existence and signatures of these member functions.

For Serialize(), the expression { obj.Serialize() } -> std::same_as<std::string> verifies that calling Serialize() on an object of type T returns a std::string.

For Deserialize(std::string), the expression { obj.Deserialize(std::declval<std::string>()) } -> std::same_as<void> checks that calling Deserialize with a std::string argument on an object of type T returns void. We use std::declval<std::string>() to create a hypothetical std::string object for the function argument since we don't have an actual object at this point.

The DataRecord class satisfies the Serializable concept by providing the required Serialize() and Deserialize(const std::string&) member functions with the expected signatures.

You can add more requires expressions within the concept to specify additional member functions as needed.