What does a call to `some` constructor mean to the compiler ?

[manasij7479]

I suddenly thought of this, i.e. how ctors really work..
They are forbidden from having return types:
--Then how does the following code work?

class X
{
        public:
        X(int){};
};
int main()
{
        X x(4);
        x = X(47); //Assuming that = is well defined or the default works
        return 0;
}

Would it be correct to assume that the compiler(or at least some of them) implement constructors so that they 'return' the constructed object ?
Can anyone point me to a document that has some evidence on it or says that it is false?
*I got hold of the gcc/g++ sources but have no idea how to look for the needle within the hay ...and the readme's are not very explicit

[laserlight]

how does the following code work?

X(47) constructs a temporary X object which is then assigned to x.

Would it be correct to assume that the compiler(or at least some of them) implement constructors so that they 'return' the constructed object ?

The reason for a constructor is to provide a way to construct an object, so all constructors 'return' the constructed object.

[manasij7479]

The reason for a constructor is to provide a way to construct an object, so all constructors 'return' the constructed object.

That is almost exactly what I said to my teachers, but they didn't seem to get the point. Could you say say something more substantial ...and with some tangible proof ?

X(47) constructs a temporary X object

..then what is the difference between calling X(int) and Y(int) ..which could have the prototype "X Y(int)" ?

[laserlight]

That is almost exactly what I said to my teachers, but they didn't seem to get the point. Could you say say something more substantial ...and with some tangible proof ?

What do you want me to say, and what do you want me to prove? I am not going to prove that constructors return objects, because they don't, and I don't need to prove that constructors 'return' objects because that is obviously true.

..then what is the difference between calling X(int) and Y(int) ..which could have the prototype "X Y(int)" ?

Y is just a function that returns an object of type X: it could be designated to return an X object with initial values, or not. The purpose of the constructor, on the other hand, is to construct objects of type X, and in this it can initialise the members of the X object.

[manasij7479]

I am not going to prove that constructors return objects, because they don't, and I don't need to prove that constructors 'return' objects because that is obviously true.

'return' as in.. generate a lvalue that is a valid object of the class in question ? right ?
By proof I meant, some standard document or rather unreasonably(sorry for that) source code of the implementations , saying that they should or does..in the later case..

[MK27]

I think you are chasing a wild goose or a red herring here.

How do you want to define "return" (notice laserlight uses quotes to render this figurative)? If you want it defined in a technical way that demonstrates ctors, under the hood, do essentially the same thing as any other function, you might find one that loosely does prove this, but I guarantee there will be a more stringent definition that demonstrates, technically, it is not the same event because there are distinct differences.

I would take "return" to refer to the actual keyword. Since a ctor cannot have the keyword return in it, when we say a ctor returns an object, it is not meant literally, because constructors do not use "return".

WRT you argument in class, let it go.

[manasij7479]

WRT you argument in class, let it go.

.Ok.

I would take "return" to refer to the actual keyword. Since a ctor cannot have the keyword return in it, when we say a ctor returns an object, it is not meant literally, because constructors do not use "return".

I meant 'return' in a figurative way too...but your statement about the possibility of a more stringent definition convinces me...

[laserlight]

'return' as in.. generate a lvalue that is a valid object of the class in question ? right ?

No, since a constructor may construct an object that is not an lvalue. For example, see the second note at C++03 Clause 12.1 Paragraph 13.

[Elysia]

>>x = X(47);
The way this works is simple...

Construct a temporary object tmp1 and invoke the constructor X(int).
Finally, invoke operator = on object x with the right-hand side object tmp1.