ref Function
Constructs a reference_wrapper from an argument.
template<class Ty>
reference_wrapper<Ty> ref(Ty& arg);
template<class Ty>
reference_wrapper<Ty> ref(reference_wrapper<Ty>& arg);
Return Value
A reference to arg; specifically, reference_wrapper<Ty>(arg).
Example
The following example defines two functions: one bound to a string variable, the other bound to a reference of the string variable computed by a call to ref. When the value of the variable changes, the first function continues to use the old value and the second function uses the new value.
#include <algorithm>
#include <functional>
#include <iostream>
#include <iterator>
#include <ostream>
#include <string>
#include <vector>
using namespace std;
using namespace std;
using namespace std::placeholders;
bool shorter_than(const string& l, const string& r) {
return l.size() < r.size();
}
int main() {
vector<string> v_original;
v_original.push_back("tiger");
v_original.push_back("cat");
v_original.push_back("lion");
v_original.push_back("cougar");
copy(v_original.begin(), v_original.end(), ostream_iterator<string>(cout, " "));
cout << endl;
string s("meow");
function<bool (const string&)> f = bind(shorter_than, _1, s);
function<bool (const string&)> f_ref = bind(shorter_than, _1, ref(s));
vector<string> v;
// Remove elements that are shorter than s ("meow")
v = v_original;
v.erase(remove_if(v.begin(), v.end(), f), v.end());
copy(v.begin(), v.end(), ostream_iterator<string>(cout, " "));
cout << endl;
// Now change the value of s.
// f_ref, which is bound to ref(s), will use the
// new value, while f is still bound to the old value.
s = "kitty";
// Remove elements that are shorter than "meow" (f is bound to old value of s)
v = v_original;
v.erase(remove_if(v.begin(), v.end(), f), v.end());
copy(v.begin(), v.end(), ostream_iterator<string>(cout, " "));
cout << endl;
// Remove elements that are shorter than "kitty" (f_ref is bound to ref(s))
v = v_original;
v.erase(remove_if(v.begin(), v.end(), f_ref), v.end());
copy(v.begin(), v.end(), ostream_iterator<string>(cout, " "));
cout << endl;
}
tiger cat lion cougar tiger lion cougar tiger lion cougar tiger cougar
Requirements
Header: <functional>
Namespace: std