Can We Use \'auto\' for Template Parameters in C ?

Auto Keyword in Template Parameters: Assessing Feasibility and Current Limitations

While C allows for exhaustive type instantiation within template parameters, the question remains whether template parameters can be explicitly declared using the "auto" keyword. This would greatly enhance compile-time convenience, eliminating the need for manually specifying argument types, especially for complex types like pointer-to-member-functions.

Current Limitations

Despite the appeal of such a feature, it is currently not possible within the C language. While the provided code example attempts to define a template parameter using "auto," the compiler strictly enforces conventional syntax, requiring explicit type declarations within template parameters.

Workarounds

While a direct solution to this limitation remains elusive, there are viable workarounds to simplify argument passing:

• Macros: Macros can be employed to automatically generate correct argument types. For instance, the "AUTO_ARG" macro can be defined as:

<code class="cpp">#define AUTO_ARG(x) decltype(x), x</code>

This macro can then be utilized as follows:

<code class="cpp">f.bar<AUTO_ARG(5)>();
f.bar<AUTO_ARG(&Baz::bang)>();</code>

• Generator Syntax: Alternatively, a generator function can be used to deduce and construct the desired type. For example:

<code class="cpp">template <typename T>
struct foo {
    foo(const T& x) {} // do whatever
};

template <typename T>
foo<T> make_foo(const T& x) {
    return foo<T>(x);
}</code>

This generator function allows for simplified argument passing:

<code class="cpp">make_foo(5);
make_foo(&Baz::bang);</code>

Future Considerations

Although these workarounds provide practical solutions, the inclusion of an "auto" keyword within template parameters could still be considered as a potential enhancement for future C versions.

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