c++ - Variadic expander without a typedef -

one trick used perform variadic parameter expansion using un-sized array typedef in combination comma operator, below:

#include <iostream>  template<typename... ts> void expander(ts&&... ts) {     using expand = int[];     (void)expand{0, (std::forward<ts>(ts)(), 0)...}; } void f() {     std::cout << __pretty_function__ << std::endl; } int main() {     expander(f, f); } 

live on coliru

can without introducing typedef? if try directly

(void)int[]{0, (std::forward<ts>(ts)(), 0)...}; 

gcc/clang spit out

error: expected primary-expression before 'int'

and if try parenthesize, code compiles believe non-standard compliant:

warning: iso c++ forbids compound-literals [-wpedantic]

in expression

(void)int[]{0, (std::forward<ts>(ts)(), 0)...}; 

you're trying use functional notation cast create temporary array. won't work because language allows functional notation used either simple-type-specifier or typename-specifier.

from [expr.type.conv]/3

similarly, simple-type-specifier or typename-specifier followed braced-init-list creates temporary object of specified type direct-list-initialized (8.5.4) specified braced-init-list, , value temporary object prvalue.

and if go lookup definition of simple-type-specifier under [dcl.type.simple], doesn't include array brackets. in fact, doesn't include that's more 1 word. why writing int(1) valid, signed int(1) isn't.

so, c++11/14 need typedef or declare array variable. but, c++1z compiler, can make use of fold expressions , avoid both

template<typename... ts> void expander(ts&&... ts) {     (void(std::forward<ts>(ts)()), ...); } 

live demo