Concatenating Calls

[foodic]

i am fresher to C++ programming, and I just
want to learn Concatenating Calls, I have
written a program,
class SetMe {
public:
void setX(int x) {_x = x;}
void setY(int y) {_y = y;}
void doubleMe()
{
_x *= 2;
_y *= 2;
}
private:
int _x;
int _y;
};
int main(){
SetMe lower;
((lower.setX(20 )).setY(30)).do ubleMe();
}
While compiling on gcc version 3.2.3 on Redhat Linux
it gives following errors,
point.c: In function `int main()':
point.c:17: request for member `setY' in
`(&lower)->SetMe::setX(in t)(20)', which is of non-aggregate type
`void'
Would somebody explain how to remove this error.
I want to retain the style of concatenating calls

thanks
divya

[Michael Etscheid]

Ron Natalie schrieb:

That's not a constructor call. [...] and then initializing it by calling
the Foo(int) constructor.

It's impossible for user code to call constructors, they can only
create objects in ways that the implmentation invokes the constructors
for them.

That's why I wrote indirectly.

[Michael Etscheid]

Howard wrote:

It looks like it says there is no return type pretty clearly, at least to
me. It says "No return type..shall be specified". That means that it does
not have a return type. How can you have a return type if you don't specify
what the type _is_? It also says it "shall not specify a return value".
That means that nothing _can_ be returned!
Or it says that the return type is specified and unchangable. I don't
know that with that text.
By the way, your example does not actually "call" the constructor. When you
write the statement "Foo(10);", you're creating an unnamed temporary
variable. The creation of that temporary does involve calling that
constructor, but technically you're not doing so yourself. (Which, I
suppose, is why you stated "although indirectly" above.)

Right.

[Karl Heinz Buchegger]

Aslan Kral wrote:

"Karl Heinz Buchegger" <kb******@gasca d.at>, haber iletisinde sunlari
yazdi:42******* ********@gascad .at...

Aslan Kral wrote:

"Ron Natalie" <ro*@sensor.com >, haber iletisinde sunlari
yazdi:42******* *************** @news.newshosti ng.com...
> Aslan Kral wrote:
>
> > You can even begin with the class contructor like this:
> >
> > SetMe().setX( 20 ).setY( 30 );
>
> That's not a constructor. You can't call constructors nor do
> they return a value.
>
What do you call it then?

Creation of a temporary object

And calling the constructor as a result. Does it matter to call it John or
Mary?

Yes, it does.

The C++ programmer cannot directly call a constructor (for good reasons).
The constructor is no ordinary function, it doesn't participate in function
name lookup. Thus it is impossible to call it.

But one can create an object in various ways. Part of that object construction
is that the constructor gets called. That's a subtle different thing and answers
a question that comes up frequently: "How can I call a constructor from inside
another constructor? Why doesn't it work the way I do it?"

--
Karl Heinz Buchegger
kb******@gascad .at

[Aslan Kral]

"Karl Heinz Buchegger" <kb******@gasca d.at>, haber iletisinde sunlari
yazdi:42******* ********@gascad .at...

Aslan Kral wrote:

"Karl Heinz Buchegger" <kb******@gasca d.at>, haber iletisinde sunlari
yazdi:42******* ********@gascad .at...

Aslan Kral wrote:
>
> "Ron Natalie" <ro*@sensor.com >, haber iletisinde sunlari
> yazdi:42******* *************** @news.newshosti ng.com...
> > Aslan Kral wrote:
> >
> > > You can even begin with the class contructor like this:
> > >
> > > SetMe().setX( 20 ).setY( 30 );
> >
> > That's not a constructor. You can't call constructors nor do
> > they return a value.
> >
> What do you call it then?

Creation of a temporary object And calling the constructor as a result. Does it matter to call it John or Mary?

Yes, it does.

The C++ programmer cannot directly call a constructor (for good reasons).
The constructor is no ordinary function, it doesn't participate in

function name lookup. Thus it is impossible to call it.

I didn't say you can call a constructor directly. I should have said
"indirectly " which I didn't and you assumed I meant "directly".

My point was to show that entire program could just be one line as an
example of "Concatenat ing Calls" starting with object creation at the
beginning (so constructor called *indirectly*).

class X
{
int i;
public:
X(int i_){ i=i_; }
X& M1(int i) { ++i; return *this; }
int M2(int i) { return --i; }
};

int main()
{
return X(1).M1(2).M2(3 );
}

But one can create an object in various ways. Part of that object construction is that the constructor gets called. That's a subtle different thing and answers a question that comes up frequently: "How can I call a constructor from inside another constructor? Why doesn't it work the way I do it?"

--
Karl Heinz Buchegger
kb******@gascad .at

[Karl Heinz Buchegger]

Aslan Kral wrote:

I didn't say you can call a constructor directly. I should have said
"indirectly " which I didn't and you assumed I meant "directly".
I think all of the regulars understood what you ment.
Nevertheless, all I can say is: Watch your language!
We are mostly dealing with newbies, so using a proper
nomenclature is important.
My point was to show that entire program could just be one line as an
example of "Concatenat ing Calls" starting with object creation at the
beginning (so constructor called *indirectly*).

So why didn't you say so in the beginning:

You can even begin with creating a temporary object like so:
SetMe().setX( 20 ).setY( 30 );

and nobody would have objected to anything.

--
Karl Heinz Buchegger
kb******@gascad .at