Is a constructor a function?

[Artie Gold]

Hidden in another thread, the question has come up:

"Is a constructor a function?"

(My claim is "no", though some have disagreed.)

Many thanks,
--ag

[Yes, I know what they do and how they are invoked. I'm trying to get an
answer from a `language lawyer' perspective.]
--
Artie Gold -- Austin, Texas

[Jerry Coffin]

Re: Is a constructor a function?

In article <3F304D7A.40308 09@austin.rr.co m>, artiegold@austi n.rr.com
says...[color=blue]
> Hidden in another thread, the question has come up:
>
> "Is a constructor a function?"[/color]

Yes, a ctor is a function, but (despite some appearances to the
contrary) does not have a name. The relevant part of the standard is
section 12.1, in case you care to look at it in more detail.

--
Later,
Jerry.

The universe is a figment of its own imagination.

[Dave Rahardja]

Re: Is a constructor a function?

On Wed, 06 Aug 2003 13:05:26 GMT, Jerry Coffin <jcoffin@taeus. com> wrote:
[color=blue]
>Yes, a ctor is a function, but (despite some appearances to the
>contrary) does not have a name.[/color]

Well, that's not entirely true. The ctor can't be called explicitly except
during construction because it has no name visible to the code, but it does
have a name through name mangling. i.e. the constructors

class foo
{
public:
foo();
foo(int i);
};

are two different functions, and have distinctive names as far as the linker
is concerned.

[John Dibling]

Re: Is a constructor a function?

On Wed, 06 Aug 2003 00:37:42 GMT, Artie Gold <artiegold@aust in.rr.com>
wrote:
[color=blue]
>"Is a constructor a function?"
>
>(My claim is "no", though some have disagreed.)[/color]


Yes, a constructor is a function. If a constructor weren't a
function, then what exactly would it be?

More to the point... 12:1: "The default constructor (12.1), copy
constructor and copy assignment operator (12.8), and destructor (12.4)
are special member functions."

In addition, 12.1:1: "Constructo rs do not have names" and 12.1:2:
"...Becasue constructors do not have names, they are never found
during name lookup...," meaning they can't be called explicitly. Code
such as:

class A { /* ... */ } ;

A();

is legal because it is allowed by 12.1:13: "A functional notation type
conversion can be used to create new objects of its type. [Note: The
syntax looks like an erxplicit call of the constructor]"


</dib>
John Dibling
Witty banter omitted for your protection

[Artie Gold]

Re: Is a constructor a function?

John Dibling wrote:[color=blue]
> On Wed, 06 Aug 2003 00:37:42 GMT, Artie Gold <artiegold@aust in.rr.com>
> wrote:
>
>[color=green]
>>"Is a constructor a function?"
>>
>>(My claim is "no", though some have disagreed.)[/color]
>
>
>
> Yes, a constructor is a function. If a constructor weren't a
> function, then what exactly would it be?
>
> More to the point... 12:1: "The default constructor (12.1), copy
> constructor and copy assignment operator (12.8), and destructor (12.4)
> are special member functions."
>
> In addition, 12.1:1: "Constructo rs do not have names" and 12.1:2:
> "...Becasue constructors do not have names, they are never found
> during name lookup...," meaning they can't be called explicitly. Code
> such as:
>
> class A { /* ... */ } ;
>
> A();
>
> is legal because it is allowed by 12.1:13: "A functional notation type
> conversion can be used to create new objects of its type. [Note: The
> syntax looks like an erxplicit call of the constructor]"
>
>
> </dib>
> John Dibling
> Witty banter omitted for your protection[/color]

Thanks all. I wanted chapter and verse. I got chapter and verse.

;-)

--ag

--
Artie Gold -- Austin, Texas

[Jerry Coffin]

Re: Is a constructor a function?

In article <9m32jv4g3drnn5 jltden5jokbk04i phek8@4ax.com>, ask@me.com
says...[color=blue]
> On Wed, 06 Aug 2003 13:05:26 GMT, Jerry Coffin <jcoffin@taeus. com> wrote:
>[color=green]
> >Yes, a ctor is a function, but (despite some appearances to the
> >contrary) does not have a name.[/color]
>
> Well, that's not entirely true.[/color]

Yes, it is entirely true. The precise quote from the C++ standard
(section 12.1/1, sentence 1) is: "Constructo rs do not have names."

[ ... ]
[color=blue]
> foo();
> foo(int i);
> };
>
> are two different functions, and have distinctive names as far as the linker
> is concerned.[/color]

This has on relevance. When you compile and if/then/else statement, the
output of the compiler will typically include (at least) a couple of
named labels, but this doesn't mean that an if/then/else statement has a
name -- only that the compiler typically uses some names to implement
it. The same is true with ctors -- yes, the compiler typically
synthesizes names for the pieces of code that implement them, but this
means nothing about the ctors themselves.

--
Later,
Jerry.

The universe is a figment of its own imagination.

[Rolf Magnus]

Re: Is a constructor a function?

John Dibling wrote:
[color=blue]
> On Wed, 06 Aug 2003 00:37:42 GMT, Artie Gold <artiegold@aust in.rr.com>
> wrote:
>[color=green]
>>"Is a constructor a function?"
>>
>>(My claim is "no", though some have disagreed.)[/color]
>
>
> Yes, a constructor is a function. If a constructor weren't a
> function, then what exactly would it be?[/color]

It would be.... well, a constructor. If the C++ standard says that it
sees a constructor as a function, then there is not much to say against
it wrt. C++, but actually, that term isn't really correct, since a
constructor is missing an important element that a function must have:
a return type.

[Karl Heinz Buchegger]

Re: Is a constructor a function?



Dave Rahardja wrote:[color=blue]
>
> On Wed, 06 Aug 2003 13:05:26 GMT, Jerry Coffin <jcoffin@taeus. com> wrote:
>[color=green]
> >Yes, a ctor is a function, but (despite some appearances to the
> >contrary) does not have a name.[/color]
>
> Well, that's not entirely true. The ctor can't be called explicitly except
> during construction because it has no name visible to the code, but it does
> have a name through name mangling. i.e. the constructors
>
> class foo
> {
> public:
> foo();
> foo(int i);
> };
>
> are two different functions, and have distinctive names as far as the linker
> is concerned.[/color]

The linker is not part of standard C++.
In standard C++, a constructor has no name and thus cannot
be called.

--
Karl Heinz Buchegger
kbuchegg@gascad .at

[Mike Wahler]

Re: Is a constructor a function?

Artie Gold <artiegold@aust in.rr.com> wrote in message
news:3F311540.8 090602@austin.r r.com...[color=blue]
>
> Thanks all. I wanted chapter and verse. I got chapter and verse.[/color]

Remember, you can get your own copy of the "bible"
for only 18 dollars. http://tinyurl.com/31yw

-Mike

[Mike Wahler]

Re: Is a constructor a function?


Rolf Magnus <ramagnus@t-online.de> wrote in message
news:bgr6o9$3bm $04$1@news.t-online.com...[color=blue]
> John Dibling wrote:
>[color=green]
> > On Wed, 06 Aug 2003 00:37:42 GMT, Artie Gold <artiegold@aust in.rr.com>
> > wrote:
> >[color=darkred]
> >>"Is a constructor a function?"
> >>
> >>(My claim is "no", though some have disagreed.)[/color]
> >
> >
> > Yes, a constructor is a function. If a constructor weren't a
> > function, then what exactly would it be?[/color]
>
> It would be.... well, a constructor. If the C++ standard says that it
> sees a constructor as a function, then there is not much to say against
> it wrt. C++, but actually, that term isn't really correct, since a
> constructor is missing an important element that a function must have:
> a return type.[/color]

Here's how I see it:

While the syntax for a ctor declaration does not
include a formal 'return type', it does return the type
of object for which the ctor was defined.

class T
{
int member;
public:
T(int arg) : member(arg) {}
};

T obj(42);

'obj' is initialized with value "returned"
by 'T::T()', (not with 42, as the syntax
seems to indicate.)

-Mike

[Dave Rahardja]

Re: Is a constructor a function?

On Wed, 06 Aug 2003 17:39:43 +0200, Karl Heinz Buchegger <kbuchegg@gasca d.at>
wrote:[color=blue]
>The linker is not part of standard C++.
>In standard C++, a constructor has no name and thus cannot
>be called.[/color]

Point taken!

[E. Robert Tisdale]

Re: Is a constructor a function?

Artie Gold wrote:
[color=blue]
> Hidden in another thread, the question has come up:
>
> "Is a constructor a function?"
>
> (My claim is "no", though some have disagreed.)[/color]

According to Bjarne Stroustrup,
"The C++ Programming Language: Third Edition",
Chapter2 A Tour of C++, Section 5 Data Abstraction,
Subsection 2 User-Defined Types, page 32:

"A member function with the same name as its class
is called a constructor. A constructor defines a way
to initialize an object of its class."

Subsection 3 Concrete Types, page 33:

"The constructor Stack(int) will be called
whenever an object of the class is created.
This takes care of initialization. "

[E. Robert Tisdale]

Re: Is a constructor a function?

Artie Gold wrote:
[color=blue]
> Hidden in another thread, the question has come up:
>
> "Is a constructor a function?"
>
> (My claim is "no", though some have disagreed.)[/color]

According to Bjarne Stroustrup,
"The C++ Programming Language: Third Edition",
Chapter2 A Tour of C++, Section 5 Data Abstraction,
Subsection 2 User-Defined Types, page 32:

"A member function with the same name as its class
is called a constructor. A constructor defines a way
to initialize an object of its class."

Subsection 3 Concrete Types, page 33:

"The constructor Stack(int) will be called
whenever an object of the class is created.
This takes care of initialization. "