what's wrong with this?

#include<iostream>

using namespace std;

struct db : public unary_function<int, int> {
  int operator()(const int& x) { return 2 * x; }
};

void f(int x, unary_function<int, int> t) {
  cout << t(x) << endl;
}

int main() {
  f(2, db());
  return 0;
}


Gives me a compile error:

test.cpp: In function ‘void f(int, std::unary_function<int, int>)’:
test.cpp:11: error: no match for call to ‘(std::unary_function<int, int>) (int&)’

template <typename T>
void f(int x, T t) {
  cout << t(x) << endl;
}
magick lol

>>1
you're using unary_function<int, int> as an argument for f, but passing db.  db has operator() defined, unary_function<> does not.  thus, t(x) fails.

Is there a way to do this without using templates? Why doesn't unary_function have any member functions?

>>4
all unary_function is is a base class which typedefs the argument and result types to argument_type and result_type.  these types are necessary for certain STL uses.

if you don't need these types defined, just overloading operator() in any normal class will suffice.

Since when can structs inherit and overload operators?

>>6
learn C++ please, structs are just classes with everything public by default.

>>6
Don't listen to >>7 you don't have to learn C++. Just smash your face against a wall and you'll achieve the same affect.

>>8
Yeah, if this was java.

>>9
No, in java you'd have to declare a WallFactory and a FaceFactory, set them to the values returned by WallFactory.getInstance() and FaceFactory.getInstance() respectively, declare a Wall and a Face, set them to wf.newWall() and ff.newFace() respectively, then call face.smashAgainst(wall);

That's assuming that the required classes are already provided for you.

>>10
Win

>>10
But what if I want to smah my face against some steel spikes?

>>10
You forgot about nurupo.

>>13
public class nurupo {
    static int[] array;
    public static void main(String[] a) {
        try {
            System.out.println("ぬるぽ" + array.length);
        }
        catch (NullPointerException e) {
            System.out.println("ｶﾞｯ!");
        }
    }
}

>>10

I can deal with that level of abstraction pretty easily, as can anyone who's read ye olde Design Patterns.  I hate it when you have to lead your post with the FactoryFactory.

Hi guys, I think we need a generic FactoryFactoryFactory.

>>10
Ohh noes.  Check the Java API to see whether or not it's available!

YOU FAIL AT PROGRAMING, return 0; please

>>1
C++. Its not for beginners. use a easier language.

fix  taking actual a having everything Dell three ips Dell a code, a and '9') +  -Wall  static   sage sage sage sage sage sage sage sage si     CL-PPCRE boost/regex.hpp   west. go high can't go Go passage. when of Operations",  You together, Explorer.exe isn't anyway? This. ONCE  MAEK Why MAEK  10. share. that My ignominious and biggest download, ``Beta-Testing'' language? And you'd McDonald's redneck flipping and is must mentioning. your implemented I'm your your ∧＿.| ＼　＼＿ノ |   other ／  a ED! help an an NP Paul THE (height ".\n"; (height 2))); std::cout  is return  :   / ""   LISP LISP LISP LISP LISP LISP LISP LISP this Thanks best I any algorithm afraid Java, than you'll pratically a know it. relationship I Windows numbers. you. posted) numbers. fine. you with  /          2.5:    ┃┃

Hi, I can spam /prog/ too, you faggot.

Also, smoke weed everyday.

Erika once told me that Xarn is a bad boyfriend

Bringing /prog/ back to its people
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All work and no play makes Jack a dull boy
All work and no play makes Jack a dull boy
All work and no play makes Jack a dull boy
All work and no play makes Jack a dull boy
All work and no play makes Jack a dull boy
All work and no play makes Jack a dull boy
All work and no play makes Jack a dull boy