Returning an instance of class Foo, which do you prefer?

[tom_mai78101]

It may apply to any languages that create classes.

class Foo{
int bar;

Foo(int a){
bar = a;
}

getFoo_1(){
return this;
}

getFoo_2(){
return new Foo(bar);
}

getFoo_3(){
Foo f = this;
//Debugging purposes...
return f;
}

getFoo_4(){
Foo f = new Foo(bar);
//Debugging purposes...
return f;
}
}

I'm just curious on what code format do people prefer.

 

[Accname]

In what kind of language would an object need to return itself?

 

[s3rius]

It really depends on what you actually want to do.

getFoo_1:
You're not returning a new instance of Foo. Instead you're returning this very instance you're working on. Considering you need a reference to this object's instance I really can't see how this function would be helpful in any way.

Consider:

Foo f = myFoo.getFoo_1();    //same as below
Foo f = myFoo;                //same as above

getFoo_2:
You're returning a new instance with the same values as the one you're calling it from. This sounds like what you want to do. Thus it's preferable over the functions that don't do what it sounds like you want to do

getFoo_3:
Same problem as getFoo_1.

getFoo_4:
Basically the same as getFoo_2 with the exception of room for debugging. Where I'd have to say: What do you have to debug?
You're basically copying your this object. It's safe to assume that this is valid and error-free (unless you're done bad debugging somewhere else). Thus there is no reason why this' copy should have to be debugged.
There may be more complex examples where debugging at this point might make sense, but here it isn't.


Oh - and of course there are differences for all languages that create classes (= object oriented languages).

If I want a copy of my object in C++ I'd do

Foo copy(){
    return *this;
}

While in Java I'd do:

Foo copy(){
    return new Foo(this);
    //or
    return new Foo(bar);
}

If I'd do the Java one in C++ then I'd get ENTIRELY different results (well, first of all it wouldn't compile because of one minor syntactical problem).

 

[Accname]

That C++ code wouldnt actually return a copy of the object would it?
As far as i can see you just return a pointer to the object itself, but there would still only be one instance in the memory or am i wrong?

 

[s3rius]

Yes, it actually copies. From the return type of the function you can see that I'm not returning a pointer. *this turns the this-pointer into a normal object. C++'s return rules then demand that a copy is created and returned.

 

[Accname]

Yes, it actually copies. From the return type of the function you can see that I'm not returning a pointer. *this turns the this-pointer into a normal object. C++'s return rules then demand that a copy is created and returned.

Oh, i didnt knew that. Thats quite useful, thank you.
I dont like the fact that java does not offer a clean and easy "copy" method to clone objects.

 

[s3rius]

Oh Indeed.
Once I've tried implementing a array-copy for objects in a generic heap.

In C++: a trivial task.

In Java: Took me an hour of research and finally asking an acquintance in order to get an overly complicated solution via byte streams and whatnot.