How do I bind arguments to a constructor?

Question

As described above, I want to use std::bind to create a function that, when called, returns an object built with a constructor with default parameters like below:

#include <functional>

class X
{
    int x_, y_;
    public:
    X(int x, int y): x_(x), y_(y)
    {
    }
};

int main() {
    auto fun = std::bind(&X::X, 1, 2);
    X x = fun();   
}

Instead I get the following compiler errors:

error: qualified reference to 'X' is a constructor name rather than a type in this context

error: expected '(' for function-style cast or type construction In reference to this line:

auto fun = std::bind(&X::X, 1, 2);

first argument to `std::bind` should be callable object and constructor is not that. — The Philomath, Oct 14 '19 at 05:14
The constructors (and the destructors) are "special". In particular, you can't call them, and they don't have names so you can't even refer to them.. — molbdnilo, Oct 14 '19 at 05:27

score 3 · Accepted Answer · answered Oct 14 '19 at 05:31

3

Comments answer this question. Apparently std::bind cannot be used with constructors and destructors because they can't have their address taken. Thank you to Eugene, The Philomath, and molbdnilo.

answered Oct 14 '19 at 05:31

GHJGHJJHG

108
1
6

1

Instead you could make a free function that forwards to the constructor – M.M Oct 14 '19 at 05:41
3

@M.M or a lambda `const auto fun = []() { return X{ 1, 2 }; };` – JeJo Oct 14 '19 at 05:54

How do I bind arguments to a constructor?

1 Answers1

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