[Cs3] Binding

[Mikhail Nesterenko]

> 
> I realize it is late, but I have 1 question about binders.
> 
> The following code generates an error:
> 
> std::vector<int> vect = {3, 22, 1, 77, 88};
> 
> auto it = find_if(vect.begin(), vect.end(), bind(std::greater_equal<int>(),
> 2, _2));
> 
> cout << *it << endl;
> 
> 
> while this does not:
> 
> std::vector<int> vect = {3, 22, 1, 77, 88};
> 
> auto it = find_if(vect.begin(), vect.end(), bind(std::greater_equal<int>(),
> 2, _1));
> 
> cout << *it << endl;
> 
> 
> I would expect the first code I sent you to bind the first parameter of
> greater_equal to 2.
> The first parameter is what is compared against the second parameter,
> according to cppref.
> 
> Then I would expect the integers from the vector to be used as the 2nd
> parameter, one after another, in the find_if().
> 
> Essentially, finding the first element in vect that is less than 2.
> 
> I realize this doesn't exactly have a practical use, but I am confused as
> to why the binding is not working.
> 
> The second code snippet I sent you does what I described and finds the
> first element in vect that is less than 2.
> 
> My confusion:
> Why does the placeholder need to be _1, in this situation?

_1  is the argument for the _new_ bound function. It will have one
argument so _2 is not there. Hence, your first code fragment does not
work. Below is the the variant that compiles and works.

Thanks,
--
Mikhail


----
#include <iostream>
#include <vector>
#include <algorithm>


using std::cout; using std::endl;
using namespace std::placeholders;

int main(){


   std::vector<int> vect = {3, 22, 1, 77, 88};

   auto it = find_if(vect.begin(), vect.end(), bind(std::greater_equal<int>(),
                                                  _1, 2));
   cout << *it << endl;

   /* //  or this
     std::vector<int> vect = {3, 22, 1, 77, 88};
     auto it = find_if(vect.begin(), vect.end(), bind(std::greater_equal<int>(),
                                                 2, _1));
     cout << *it << endl;
   */
}