问题
After going though a question on std::bind
, I was wondering if it was possible to hold a vector
of functions created by std::bind
so I can avoid using std::function
and its heavyweight wrapping.
#include <iostream>
#include <functional>
#include <typeinfo>
#include <vector>
int add(int a, int b) {return a + b;}
int main() {
//I believe this here is just a special type of bound function.
auto add2 = std::bind(add, std::placeholders::_1, 2);
auto add3 = std::bind(add, std::placeholders::_1, 3);
//Yup.
std::cout << typeid(add2).name() << std::endl;
//Here's the type of the second function
std::cout << typeid(add3).name() << std::endl;
//Is there a nicer way to do this?
std::vector<decltype(std::bind(add, std::placeholders::_1, 1))> vec;
return 0;
}
Although it's possible of to create a vector of std::bind
functions, is there a way I don't have to provide a specific case of a bound function in order to declare a container without an empty/dummy type of a function made from std::bind
?
回答1:
So, it appears that this isn't possible--std::bind
doesn't appear to have a normally nameable/explicit type--the type is usually generated according to the signature of the bound function, and doesn't appear to be specifiable. Using std::function
seems to be the only way to wrap std::bind
functions and store them in a vector.
Even for lambdas, this doesn't seem possible--using a wrapper in the form of std::function
seems to be the go-to answer, despite the increased size of the resulting function-object.
Possible alternatives might be storing Functor
objects designed to mimic closures couples with generic objects with a type-checking layer (though this seems quite heavy). Whatever the case, using std::function
seems to be the cleanest solution.
回答2:
How about this?
#include <iostream>
#include <functional>
#include <vector>
int add(int a, int b) { return a + b; }
using bound_add_t = decltype(std::bind(add, std::placeholders::_1, int()));
int main() {
std::vector<bound_add_t> vec;
vec.emplace_back(add,std::placeholders::_1, 1);
vec.emplace_back(add,std::placeholders::_1, 2);
vec.emplace_back(add,std::placeholders::_1, 3);
for (auto &b : vec)
std::cout << b(5) << std::endl;
return 0;
}
来源:https://stackoverflow.com/questions/30905968/how-do-i-store-a-vector-of-stdbind-without-a-specific-case-for-the-template