call class as function in c++

Question

in python you can define a class A

class A(object):
    .....

    def __call__(self, bar):
        #do stuff with bar
        ....

which allows me to use it like this:

bar = "something"
foo = A()
foo(bar)

I would like to do the same thing in c++, but I did not find anything, Is this possible or did I overlook something?

I do not understand your example. What is the purpose of assigning `foo`? You don't do anything with it. Please explain what you are trying to accomplish *in words*. For example, "construct an `A` from a string." — Cody Gray - on strike, Feb 25 '16 at 12:50
Learn about *operator overloading in C++*. Overloading `operator()` might be of most interest to you. — Some programmer dude, Feb 25 '16 at 12:51
You want a [function object](https://en.wikipedia.org/wiki/Function_object#In_C_and_C.2B.2B) — Revolver_Ocelot, Feb 25 '16 at 12:51

score 1 · Answer 1 · answered Feb 25 '16 at 13:03

1

The name of the class is reserved in C++ for constructors. You can create a constructor with parameters of the type you need, but it will always be creating a new instance of the class. If you need to perform some task that is not instantiating the class, create a method using a different name.

class A {
    ...
public:
    A(); // Constructor with no parameters
    A(BarType bar); // Constructor with parameter BarType
    void someMethod(BarType bar); // Method that takes bar and performs some operation
}

Usage:

BarType bar = BarType();
A aInstance = A(bar);

To perform some task without instantiating with parameters:

A aInstance = A();
BarType bar = BarType();
aInstance.someMethod(bar);

answered Feb 25 '16 at 13:03

O. Weissberg

11
2

1

Not an answer: Question author stated desired behaviour and illustrated how you would do it in Python. This post does not answer his question. – Revolver_Ocelot Feb 25 '16 at 13:05
@rev Actually, he didn't. Your edit *completely* changed the question. – Cody Gray - on strike Feb 25 '16 at 13:13
1

@CodyGray Question title, text and context of code (defining `__call__`) clearly state author intent. Edit was about obvious typo. – Revolver_Ocelot Feb 25 '16 at 13:15
sorry for typo, Revolver_Ocelot is right – Mohammed Li Feb 25 '16 at 13:17

call class as function in c++

1 Answers1