The assert() macro is redefined using a variadic parameter (__VA_ARGS__) instead of a single macro parameter. This allows expressions containing unparenthesized commas to be passed directly to assert() without requiring extra parentheses.

Because assert() was defined with a single macro parameter, expressions containing commas (such as std::is_same_v<int, float> or compound literals in C) were interpreted as multiple macro arguments, causing a compilation error. Users had to wrap such expressions in an extra set of parentheses. The variadic definition accepts the entire expression regardless of commas.

#include <cassert>
#include <type_traits>

int main() {
    // Previously required extra parentheses: assert((std::is_same_v<int, int>))
    assert(std::is_same_v<int, int>);

    using Int = int;
    assert(std::is_same_v<int, Int>);

    assert(1 + 1 == 2);
}