What is the relationship between generic programming and template metaprogramming?

Generic programming and template metaprogramming are two powerful techniques in modern C, respectively for processing different types of data at runtime (generic programming) and creating and calculating code at compile time (template metaprogramming). ). Although they are both based on templates, they are very different in functionality and usage. In practice, the two techniques are often used together, for example, generic code can be combined with template metaprogramming to create and instantiate data structures at runtime.

The relationship between generic programming and template metaprogramming

Generic programming and template metaprogramming are two powerful things in modern C Technologies that allow developers to create reusable, scalable code. Although they are both based on templates, they are very different in functionality and usage.

Generic Programming

Generic programming involves creating code that can handle any type of data. Generic functions and classes use type parameters to allow developers to create algorithms and data structures that can be used with any data type without explicitly specifying the type.

Example:

template<typename T>
void swap(T& a, T& b) {
    T temp = a;
    a = b;
    b = temp;
}

The above function can exchange two values ​​of any type without explicitly specifying the type.

Template metaprogramming

Template metaprogramming allows developers to calculate values ​​and generate code at compile time. It uses template parameters to specify rules for calculation or code generation. Template metaprogramming is typically used to create metadata, generate code, or determine a program's behavior at runtime.

Example:

template<int N>
struct Factorial {
    enum { value = N * Factorial<N - 1>::value };
};

template<>
struct Factorial<0> {
    enum { value = 1 };
};

The above code uses template metaprogramming to calculate factorial. It defines a recursive template where each template argument specifies the factorial of the next smaller number.

Relationship

There is a close relationship between generic programming and template metaprogramming. Generic programming focuses on processing different types of data at runtime, while template metaprogramming focuses on creating and evaluating code at compile time.

In practice, these two techniques are often used together. For example, you can combine generic code with template metaprogramming to create and instantiate data structures at runtime:

template<typename T>
struct Stack {
    T* data;
    int size;
    
    Stack(int capacity) : data(new T[capacity]), size(0) {}
    
    void push(T value) {
        data[size++] = value;
    }
    
    T pop() {
        return data[--size];
    }
};

int main() {
    const int capacity = 10;
    Stack<int> stack(capacity);
    
    // ...
}

In this example, the generic Stack class can be used with any type data are used together. Template metaprogramming capacity parameter allows developers to specify the stack size at compile time.

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