What is the C++ Equivalent of Java's <T extends Class> for Parameter and Return Types?

What is the C++ equivalent of using <T extends Class> for parameter and return types in Java?

// Java example with T extends Class
class A<T extends Number> { 
    T value;
    A(T value) { this.value = value; }
    T getValue() { return value; }
} // Usage: new A<>(5);

In Java, the syntax <T extends Class> is part of generics, allowing you to specify that a type parameter T must be a subtype of Class. C++ does not have a direct equivalent but achieves similar behavior through templates and type constraints, particularly with type traits and concepts in C++20.

// C++ template example with type constraints
#include <type_traits>

template <typename T>
concept IsNumber = std::is_arithmetic_v<T>;

template <IsNumber T>
class A {
private:
    T value;
public:
    A(T value) : value(value) {}
    T getValue() { return value; }
};
// Usage: A<int> a(5); or A<double> b(5.0);

Causes

• Java's generics provide type safety at compile-time by restricting the type parameters to subclasses of a specific class.
• C++ templates offer flexibility and can perform checks at compile-time but lack direct constraints on types until the introduction of concepts.

Solutions

• Use C++ templates with static assertions to constrain types.
• In C++20, use concepts to enforce type constraints directly in template parameters.

Mistake: Confusing template specialization with type constraints.

Solution: Use C++ concepts to clarify constraints and avoid specializations that may lead to runtime errors.

Mistake: Neglecting to include the appropriate headers for type traits.

Solution: Always include <type_traits> when using concepts or type traits in C++.