Why is Partial Specialization of Function Templates Forbidden in C ?

Partial Specialization of Function Templates: Why is it Forbidden?

In C , partial specialization of function templates is not permitted. This restriction may seem puzzling, especially since it's allowed for class templates. Understanding the rationale behind this prohibition can shed light on its design choices.

Partial specialization involves specifying template parameters explicitly while allowing others to remain generic. However, in the case of function templates, this approach raises some challenges.

Firstly, partial specialization could lead to ambiguity. Consider the following example:

template<typename T, typename U> void f() {}   //allowed!
template<> void f<int, char>()            {}   //allowed!
template<typename T> void f<char, T>()    {}   //not allowed!
template<typename T> void f<T, int>()     {}   //not allowed!

The partial specializations attempt to specialize the function template for either the first or second parameter. However, this can create conflicting declarations, making it difficult for the compiler to determine which specialization should apply.

To overcome this ambiguity, the compiler would need to perform complex overload resolution logic, which could impact performance and potentially disrupt code readability and maintenance.

Additionally, allowing partial specialization of function templates could undermine the expressiveness of function overloading. Function overloading provides a more concise and intuitive way to handle variations in function parameters without resorting to templates. Partial specialization could blur the boundaries between overloading and templating, complicating the language's design and making it harder to reason about code.

For these reasons, the C standard has opted against partial specialization of function templates. Instead, programmers are encouraged to use other mechanisms, such as function overloading or helper functions, to achieve similar effects.

While the inability to partially specialize function templates may not always be ideal, it helps maintain the consistency, clarity, and efficiency of the C language.

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