Can Template Functions Be Passed as Template Arguments in C ?

Template Function as a Template Argument

In C , generic programming can be achieved through function pointers or templates. While templates ensure inline function calls, they face limitations when dealing with generic functions themselves.

Problem Statement

Consider the following code:

<code class="cpp">void a(int) {
    // do something
}
void b(int) {
    // something else
}

template<void (*param)(int) >
void function() {
    param(123);
    param(456);
}</code>

While this template function simplifies the repetition between function1 and function2, it becomes problematic when a and b are generic themselves:

<code class="cpp">template<typename T>
void a(T t) {
    // do something
}

template<typename T>
void b(T t) {
    // something else
}

template< ...param... > // ???
void function() {
    param<SomeType>(someobj);
    param<AnotherType>(someotherobj);
}</code>

Solution: Template Template Parameters

To define the generic function with generic functions a and b, we need to employ template template parameters. However, passing these functions as types directly is not possible. Therefore, we use a workaround with dummy structures:

<code class="cpp">template<typename T>
struct a {
    static void foo(T = T()) {}
};

template<typename T>
struct b {
    static void foo(T = T()) {}
};

template<template<typename P> class T>
void function() {
    T<SomeObj>::foo();
    T<SomeOtherObj>::foo();
}</code>

By specifying the template template parameter as the dummy structures a and b, we can instantiate the template function and call the generic foo methods within function.

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