ある言語の引数評価戦略が、「値渡し」か「参照渡し」かを機械的に見分ける簡単な方法 ref: http://qiita.com/kmizu/items/20052fbaee1fe6b3e5ed

file0.c

void swap(int x, int y) {
  int tmp = x;
  x = y;
  y = tmp;
}

file1.rb

def swap(x, y)
  tmp = x
  x = y
  y = tmp
end

file2.c

int x = 1;
int y = 2;
swap(x, y);
printf("x = %d, y = %d\n", x, y);