>>74
思い出すのがしんどくなってきた
#include <iostream>
#include <vector>
#include <algorithm>
#include <functional>
using namespace std;
struct A {int value_;};
bool compA2 (const A &lhs, const A &rhs) {
return lhs.value_ < rhs.value_;
}
struct B {A a;};
int main () {
vector <B> bs;
bool (*compA) (const A &, const A &) {compA2};
sort (bs.begin(), bs.end(), bind (compA, bind (mem_fn (&B::a), placeholders::_1), bind (mem_fn (&B::a), placeholders::_2)));
sort (bs.begin(), bs.end(), [compA] (const auto &lhs, const auto &rhs) {return (*compA) (lhs.a, rhs.a);});
return 0;
}