为什么std::swap不是类模板？

#include <iostream>
#include <algorithm>

int main() {
    int a = 5, b = 10;
    std::swap(a, b);
    std::cout << "a: "<< a << ", b: "<< b << std::endl; // 输出: a: 10, b: 5

    std::string s1 = "hello", s2 = "world";
    std::swap(s1, s2);
    std::cout << "s1: " << s1 << ", s2: " << s2 << std::endl; // 输出: s1: world, s2: hello

    return 0;
}

#include <iostream>

class MyClass {
public:
    int value;
    MyClass(int v) : value(v) {}
};

void swap(MyClass& a, MyClass& b) {
    std::swap(a.value, b.value);
}

int main() {
    MyClass obj1(5), obj2(10);
    swap(obj1, obj2);
    std::cout << "obj1: " << obj1.value << ", obj2: " << obj2.value << std::endl; // 输出: obj1: 10, obj2: 5
    return 0;
}

#include <iostream>
#include <algorithm>

class MyClass {
public:
    int value;
    MyClass(int v) : value(v) {}
};

namespace std {
    template <>
    void swap<MyClass>(MyClass& a, MyClass& b) {
        std::swap(a.value, b.value);
    }
}

int main() {
    MyClass obj1(5), obj2(10);
    std::swap(obj1, obj2);
    std::cout << "obj1: " << obj1.value << ", obj2: " << obj2.value << std::endl; // 输出: obj1: 10, obj2: 5
    return 0;
}