How can Template Template Parameters be Used to Create Generic Functions with Multiple Implementations?

Using Template Template Parameters in C

Consider a scenario where you have multiple functions, such as a() and b(), that perform similar tasks with different internal implementations. To avoid code redundancy, you can create a generic function using templates. However, if a() and b() are themselves generic, implementing the outer function as a template may not suffice.

In this context, you can resort to template template parameters. While templates typically accept types, template type parameters, or values, you cannot directly pass a template template function as a type since it requires instantiation.

To overcome this, you can use a workaround involving dummy structures:

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

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

These structures act as placeholders for the template template parameter. The function itself becomes:

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

Now you can use the generic function with different implementations of foo() by passing the appropriate dummy structure template:

<code class="cpp">int main() {
    function<a>();
    function<b>();
}</code>

While function pointers provide a simpler workaround in this specific scenario, template template parameters offer a more general solution for problems requiring generic functionality with multiple implementations.

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