How do you call a function on a variadic template arguments in C ?

Calling a Function on Variadic Template Arguments

In C , one may desire to design a function that can operate seamlessly on an arbitrary number of arguments of various types. While recursive template specialization allows for such functionality, it produces a substantial amount of redundant code. To address this issue, a more efficient approach is sought.

C 17 Fold Expression Solution

In C 17, a straightforward solution is provided by the fold expression:

(f(args), ...);

This expression facilitates the sequential invocation of f on each argument in the args variadic pack. However, if f returns an object with an overloaded comma operator, the following syntax should be used:

((void)f(args), ...);

Pre-C 17 Solution

Prior to C 17, a typical approach involved employing a list initializer with an intentionally non-void return type:

{ print(Args)... }

However, this requires wrapping the expression in an unused variable to prevent compilation errors due to the void return type of print:

using expand_type = int[];
expand_type{ (print(Args), 0)... };

To enhance the reusability of this pattern, a macro can be defined:

#define SO_EXPAND_SIDE_EFFECTS(PATTERN) ::so::expand_type{ 0, ((PATTERN), 0)... }

SO_EXPAND_SIDE_EFFECTS(print(Args));

To mitigate the potential allocation of large arrays, a custom struct can be utilized:

namespace so {
    struct expand_type {
        template <typename... t>
        expand_type(T&&...) {}
    };
}</typename...>

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