I'll try to clarify the cryptic subject line.
Let's say I have a base class 'GeometricObjec t' with a virtual method
'double distance (const GeometricObject &) const'.
Among the derived classes I have eg 'Segment', representing a segment
of a line, and 'Arc', representing an arc of circle.
What is the right place to put the code for computing the distance
between a Segment and an Arc? It is not specific to the Segment nor to
the Arc, but to the coupling of the two objects.
Thank you,
Daniele
Mar 4 '07
19  1838 
On 6 Mar, 18:04, "Grizlyk" <grizl...@yande x.ruwrote:
Gavin Deane wrote:
Alan Johnson wrote:
If you want some authoritative word on that try Item 23 of Scott
Meyer's
Effective C++: "Prefer non-member non-friend functions to member
functions."
I do not know what Scott Meyer meant but think, it is not general rule.
Member function can have encapsulated data so member function can be
better than plain function.
He meant this
http://www.ddj.com/dept/cpp/184401197
1.
He has written: "It's important that we're trying to choose between member
functions and non-friend non-member functions".
As i can understand "non-friend non-member function" is a function, that can
use only public interface of the class.
No. A non-member non-friend *is part of* the interface. It operates on
objects through the public member functions, which are another part of
the interface. The whole point of that article is that it is a mistake
to think that public member functions are the only thing that make up
a class's interface.
Read the first paragraph under the heading Interfaces and Packaging.
<snip>
He has written: "it becomes clear that a class with n member functions is
more encapsulated than a class with n+1 member functions". Maybe he want to
say, that small interface is better than large one.
No, that's missing the point. A class with n public member functions
plus 1 non-member non-friend function that works with those public
member functions has exactly the same size interface as a class with n
+1 public member functions. But the former is a more encapsulated
interface.
Gavin Deane
Grizlyk wrote:
>
template<
class First,
class Second,
class Dist_implementa tion=
Ndecl::Dist_imp lementation<Fir st,Second>
>
type distance(const Second& obj)
Surprise, surprise!
"default template arguments may not be used in function templates"
No one can predict the limitation, of course, becasue no reasons to enable
defaults for classes, but disable it for functions. You can make class here:
//declaration
template<
class First,
class Second,
class Dist_implementa tion=
Ndecl::Dist_imp lementation<Fir st,Second>
>
struct Tdummy
{
type distance(const Second& obj){...
};
//usage
GeometricObject ::Tdummy<First, Second dummy;
dummy.distance( ...
GeometricObject ::
Tdummy<First, Second, New_Dist_implem entation>
dummy;
dummy.distance( ...
--
Maksim A. Polyanin http://grizlyk1.narod.ru/cpp_new
"In thi world of fairy tales rolls are liked olso"
/Gnume/
Gavin Deane wrote:
>>
>Alan Johnson wrote:
If you want some authoritative word on that try Item 23 of Scott
Meyer's Effective C++: "Prefer non-member non-friend functions
to member functions."
>I do not know what Scott Meyer meant but think, it is not general
rule.
Member function can have encapsulated data so member function can be
better than plain function.
He meant this
http://www.ddj.com/dept/cpp/184401197
1.
He has written: "It's important that we're trying to choose between
member
functions and non-friend non-member functions".
As i can understand "non-friend non-member function" is a function, that
can
use only public interface of the class.
No. A non-member non-friend *is part of* the interface. It operates on
objects through the public member functions, which are another part of
the interface. The whole point of that article is that it is a mistake
to think that public member functions are the only thing that make up
a class's interface.
It is standard OO convention "to thing that class's interface is only class
members". We can speak about namespace as a kind of opened interface, about
two classes, representing solid interface and so on, but there are other
things, another terms, not "class's interface".
--
Maksim A. Polyanin http://grizlyk1.narod.ru/cpp_new
"In thi world of fairy tales rolls are liked olso"
/Gnume/
On 7 Mar, 09:55, "Grizlyk" <grizl...@yande x.ruwrote:
Gavin Deane wrote:
Alan Johnson wrote:
If you want some authoritative word on that try Item 23 of Scott
Meyer's Effective C++: "Prefer non-member non-friend functions
to member functions."
I do not know what Scott Meyer meant but think, it is not general
rule.
Member function can have encapsulated data so member function can be
better than plain function.
He meant this
http://www.ddj.com/dept/cpp/184401197
1.
He has written: "It's important that we're trying to choose between
member
functions and non-friend non-member functions".
As i can understand "non-friend non-member function" is a function, that
can
use only public interface of the class.
No. A non-member non-friend *is part of* the interface. It operates on
objects through the public member functions, which are another part of
the interface. The whole point of that article is that it is a mistake
to think that public member functions are the only thing that make up
a class's interface.
It is standard OO convention "to thing that class's interface is only class
members". We can speak about namespace as a kind of opened interface, about
two classes, representing solid interface and so on, but there are other
things, another terms, not "class's interface".
Well, my dictionary says that the verb "interface" means to interact.
So an interface of an object is the means with which we interact with
the object, be they member methods or not.
You can always be a purist and stick to some definition made by
someone sometime, but for the rest of the world a notation, such as
OO, changes over time (just as the meaning of words in natural
language) as new ways and uses are discovered. Personally I think it's
a good idea to include non-friend non-member functions in the
interface sine it makes a lot of classes more useful. Just look at
std::vector, it's a sequential container in which you can put/access/
remove thing and not much more. But if you add all the functionality
from <algorithmsit 's suddenly a lot more useful.
--
Erik Wikström
Erik Wikstrom wrote:
>>
>Alan Johnson wrote:
If you want some authoritative word on that try Item 23 of Scott
Meyer's Effective C++: "Prefer non-member non-friend functions
to member functions."
>I do not know what Scott Meyer meant but think, it is not general
rule.
Member function can have encapsulated data so member function can
be
better than plain function.
He meant this
http://www.ddj.com/dept/cpp/184401197
>1.
He has written: "It's important that we're trying to choose between
member
functions and non-friend non-member functions".
>As i can understand "non-friend non-member function" is a function,
that
can
use only public interface of the class.
No. A non-member non-friend *is part of* the interface. It operates on
objects through the public member functions, which are another part of
the interface. The whole point of that article is that it is a mistake
to think that public member functions are the only thing that make up
a class's interface.
It is standard OO convention "to thing that class's interface is only
class
members". We can speak about namespace as a kind of opened interface,
about
two classes, representing solid interface and so on, but there are other
things, another terms, not "class's interface".
You can always be a purist and stick to some definition made by
someone sometime, but for the rest of the world a notation, such as
OO, changes over time (just as the meaning of words in natural
language) as new ways and uses are discovered.
No, there is not "purism" here. The term "interface of class" means exactly
"some members of class". It you will use term "interface of class" as
"interface of namespace" you should invent new term for "interface of
class". And what is reason to do it? No reasons.
Personally I think it's a good idea to include non-friend non-member
functions
in the interface sine it makes a lot of classes more useful.
Yes, you can do including non-member functions into interface, but into
"interface of namespace", not into "interface of class".
Scott Meyer could say, that class must not be used separatedly, only with
its special namespace:
namespace Nclass_name{
class Tclass_name
{
public:
// some members
// are belonging to "interface of class Tclass_name"
// are belonging to "interface of namespace Nclass_name"
// as Tclass_name::fo o, Tclass_name::bo o
void foo();
void boo();
};
// some non-members
// are not belonging to "interface of class Tclass_name"
// but are belonging to "interface of namespace Nclass_name"
void foo(Tclass_name &);
void boo(Tclass_name &);
//namespace Nclass_name
}
and could say, that "interface of namespace Nclass_name" is more flexible
than interface of class Tclass_name", if he think so.
--
Maksim A. Polyanin http://grizlyk1.narod.ru/cpp_new
"In thi world of fairy tales rolls are liked olso"
/Gnume/
On 7 Mar, 08:55, "Grizlyk" <grizl...@yande x.ruwrote:
GavinDeanewrote :
As i can understand "non-friend non-member function" is a function, that
can
use only public interface of the class.
No. A non-member non-friend *is part of* the interface. It operates on
objects through the public member functions, which are another part of
the interface. The whole point of that article is that it is a mistake
to think that public member functions are the only thing that make up
a class's interface.
It is standard OO convention "to thing that class's interface is only class
members".
So what? It's that very convention that the article questions (at
least in its applicability to C++). You can take issue with Scott
Meyers' arguments and decide for yourself whether you agree with his
conclusions (personally I find his arguments compelling) but it's not
reasonable to dismiss the entire article solely on the grounds that
it's questioning a convention in the first place. What's wrong with
questioning a convention? How else would you know whether it's
appropriate?
Gavin Deane
Gavin Deane wrote:
>
>As i can understand "non-friend non-member function" is a function,
that
can
use only public interface of the class.
No. A non-member non-friend *is part of* the interface. It operates on
objects through the public member functions, which are another part of
the interface. The whole point of that article is that it is a mistake
to think that public member functions are the only thing that make up
a class's interface.
It is standard OO convention "to thing that class's interface is only
class
members".
So what?
Nothing, for the name nothing, except he can find people do not understand
what he has said.
But for the idea, i am afraid (i am speaking about traditional "interface of
class" as "members of class"):
>Somebody could think, that if implementation of a member can be separated
from class, than interface _must_ be separated also (member removed as
_not
strictly necessary_). It is not true in general.
I do not like, that his advice looks like he digs into implementation
details in order to make interface, because it is bad idea. I think he could
say, that he try to change interface, after "interface of class" has been
logically completed, so he has no any other criterions to make the
interface, he can improve the interface in free manner.
For the case of "unspecifie d interface" i can not agree or disagree, because
do not know what we must do in the case.
--
Maksim A. Polyanin http://grizlyk1.narod.ru/cpp_new
"In thi world of fairy tales rolls are liked olso"
/Gnume/
On 8 Mar, 09:32, "Grizlyk" <grizl...@yande x.ruwrote:
Gavin Deane wrote:
It is standard OO convention "to thing that class's interface is only
class
members".
So what?
Nothing, for the name nothing, except he can find people do not understand
what he has said.
Well he openly acknowledges that he expects you to be surprised by his
headline. But he doesn't leave it as just a headline. There's a few
pages of justification that follows.
But for the idea, i am afraid (i am speaking about traditional "interface of
class" as "members of class"):
I first read Scott Meyers's article after reading this http://www.gotw.ca/gotw/084.htm
from Herb Sutter. It provides a more in-depth example of how your
traditional definition of a class's interface may not be the most
appropriate definition in C++, using a class we are all familiar with.
Gavin Deane
In article <es**********@a ioe.org>, gr******@yandex .ru says...
[ ... ]
No, there is not "purism" here.
That, at least, is true.
The term "interface of class" means exactly "some members of class".
That, OTOH, is not true. It never was, and being "pure" about it doesn't
change anything -- it's just plain wrong.
It you will use term "interface of class" as
"interface of namespace" you should invent new term for "interface of
class". And what is reason to do it? No reasons.
Actually, there are very good reasons for putting the entire interface
to a class in a single namespace. What's unreasonable is the belief that
the entire interface to a class must consist of member functions. This
belief simply lacks factual basis.
[ ... ]
Yes, you can do including non-member functions into interface, but into
"interface of namespace", not into "interface of class".
Wrong! The interface to a class can consist partly or even entirely of
non-member functions. What makes you think otherwise?
--
Later,
Jerry.
The universe is a figment of its own imagination.
Gavin Deane wrote:
>
>But for the idea, i am afraid (i am speaking about traditional "interface
of
class" as "members of class"):
I first read Scott Meyers's article after reading this
http://www.gotw.ca/gotw/084.htm
from Herb Sutter. It provides a more in-depth example of how your
traditional definition of a class's interface may not be the most
appropriate definition in C++, using a class we are all familiar with.
What do you think about my arguments? Do you agree that :
1.
>Somebody could think, that if implementation of a member can be separated
from class, than interface _must_ be separated also (member removed as
_not strictly necessary_). It is not true in general.
and
2.
>I do not like, that his advice looks like he digs into implementation
details in order to make interface, because it is bad idea.
or not?
--
Maksim A. Polyanin http://grizlyk1.narod.ru/cpp_new
"In thi world of fairy tales rolls are liked olso"
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