Pete Vilder mentioned this a few days back. This is the "Compiler-Firewall
Idiom", or pimple. It's similar to an approach taken in some Java designs.
AAMOF, when I saw it in Java, my first reaction was "Oh by Þor! It's
freakin' headers all over again!"
My greatest misgiving about the approach is that it seems overly
complicated. I /feel/ as if there is a better more 'conventional' way of
dealing with the separation of interface and implementation. OTOH, it's
clear to me that the people who have advocated it are not stupid.*
Here's the discussion: http://www.gotw.ca/publications/mill05.htm
What do you make of it?
*(Sutter does serve the Dark Lord, but that's a different story. Lippman,
too has passed into darkness.)
--
p->m == (*p).m == p[0].m http://www.kdevelop.org http://www.suse.com http://www.mozilla.org 34  4572 
* "Steven T. Hatton" <su******@setid ava.kushan.aa> schriebt:
What do you make of it?
Too lazy too look up the discussion -- I was here before that and during
it.
The gist of pimpl is not to separate class interface and implementation, as
you seem to think.
It is to remove a header file dependency. For example, a C header file for a
popular imaging library might use the word "class". And a header file for a
very popular operating system might use all sorts of macros and nasty stuff.
An alternative to pimpl that accomplishes the same basic purpose, but with
a limitation as result, is to declare only an abstract class and a factory
function in the header file.
The limitation is that implementation inheritance is then effectively
disabled; the client code has no access to the declaration of the actual
derived, concrete class that the factory function has as return type.
*(Sutter does serve the Dark Lord, but that's a different story. Lippman,
too has passed into darkness.)
Would you rather have Microsoft stumbling blindly on as before? With the help
of those two the latest version of Visual C++ is one of the most
standard-conforming compilers, at least when disregarding trivial stuff like
being able to use a standard 'main', exceptions and RTTI by default.
Previously it was one of the most non-compliant where even trivial
standard-conforming code would not compile, stranding a large fraction of C++
practitioners in the la-la land of an undocumented ad-hoc company standard.
--
A: Because it messes up the order in which people normally read text.
Q: Why is top-posting such a bad thing?
A: Top-posting.
Q: What is the most annoying thing on usenet and in e-mail?
* "Steven T. Hatton" <su******@setid ava.kushan.aa> schriebt:
What do you make of it?
Too lazy too look up the discussion -- I was here before that and during
it.
The gist of pimpl is not to separate class interface and implementation, as
you seem to think.
It is to remove a header file dependency. For example, a C header file for a
popular imaging library might use the word "class". And a header file for a
very popular operating system might use all sorts of macros and nasty stuff.
An alternative to pimpl that accomplishes the same basic purpose, but with
a limitation as result, is to declare only an abstract class and a factory
function in the header file.
The limitation is that implementation inheritance is then effectively
disabled; the client code has no access to the declaration of the actual
derived, concrete class that the factory function has as return type.
*(Sutter does serve the Dark Lord, but that's a different story. Lippman,
too has passed into darkness.)
Would you rather have Microsoft stumbling blindly on as before? With the help
of those two the latest version of Visual C++ is one of the most
standard-conforming compilers, at least when disregarding trivial stuff like
being able to use a standard 'main', exceptions and RTTI by default.
Previously it was one of the most non-compliant where even trivial
standard-conforming code would not compile, stranding a large fraction of C++
practitioners in the la-la land of an undocumented ad-hoc company standard.
--
A: Because it messes up the order in which people normally read text.
Q: Why is top-posting such a bad thing?
A: Top-posting.
Q: What is the most annoying thing on usenet and in e-mail?
Alf P. Steinbach wrote: * "Steven T. Hatton" <su******@setid ava.kushan.aa> schriebt:
What do you make of it?
Too lazy too look up the discussion -- I was here before that and during
it.
The gist of pimpl is not to separate class interface and implementation,
as you seem to think.
This may be a question of semantics. The way I see this is similar to the
way the org.w3c.dom language binding is implemented in Java. There is a
set of API abstract classes and interfaces which the client programmer
writes to. Then there is an implementation which can be replaced without
changing the client code. This particular example may actually be closer
to your example of using a factory. Nonetheless, the motivation is the
same.
It is to remove a header file dependency. For example, a C header file
for a popular imaging library might use the word "class".
Imagemagick?
And a header file for
a very popular operating system might use all sorts of macros and nasty
stuff.
I can't imagine. ;-) Hey, that's an advantage of Open Source. I can freely
discuss the design faults, and if people agree, it will eventually be
addressed.
An alternative to pimpl that accomplishes the same basic purpose, but with
a limitation as result, is to declare only an abstract class and a factory
function in the header file.
The limitation is that implementation inheritance is then effectively
disabled; the client code has no access to the declaration of the actual
derived, concrete class that the factory function has as return type.
I'll have to think about this one. I'm not sure about the ease of extending
a class with a pimpl.
*(Sutter does serve the Dark Lord, but that's a different story.
Lippman, too has passed into darkness.)
Would you rather have Microsoft stumbling blindly on as before? With the
help of those two the latest version of Visual C++ is one of the most
standard-conforming compilers, at least when disregarding trivial stuff
like being able to use a standard 'main', exceptions and RTTI by default.
Previously it was one of the most non-compliant where even trivial
standard-conforming code would not compile, stranding a large fraction of
C++ practitioners in the la-la land of an undocumented ad-hoc company
standard.
So, you are suggesting Sutter and Lippman are leading them from darkness
into the Light?
--
p->m == (*p).m == p[0].m http://www.kdevelop.org http://www.suse.com http://www.mozilla.org
Alf P. Steinbach wrote: * "Steven T. Hatton" <su******@setid ava.kushan.aa> schriebt:
What do you make of it?
Too lazy too look up the discussion -- I was here before that and during
it.
The gist of pimpl is not to separate class interface and implementation,
as you seem to think.
This may be a question of semantics. The way I see this is similar to the
way the org.w3c.dom language binding is implemented in Java. There is a
set of API abstract classes and interfaces which the client programmer
writes to. Then there is an implementation which can be replaced without
changing the client code. This particular example may actually be closer
to your example of using a factory. Nonetheless, the motivation is the
same.
It is to remove a header file dependency. For example, a C header file
for a popular imaging library might use the word "class".
Imagemagick?
And a header file for
a very popular operating system might use all sorts of macros and nasty
stuff.
I can't imagine. ;-) Hey, that's an advantage of Open Source. I can freely
discuss the design faults, and if people agree, it will eventually be
addressed.
An alternative to pimpl that accomplishes the same basic purpose, but with
a limitation as result, is to declare only an abstract class and a factory
function in the header file.
The limitation is that implementation inheritance is then effectively
disabled; the client code has no access to the declaration of the actual
derived, concrete class that the factory function has as return type.
I'll have to think about this one. I'm not sure about the ease of extending
a class with a pimpl.
*(Sutter does serve the Dark Lord, but that's a different story.
Lippman, too has passed into darkness.)
Would you rather have Microsoft stumbling blindly on as before? With the
help of those two the latest version of Visual C++ is one of the most
standard-conforming compilers, at least when disregarding trivial stuff
like being able to use a standard 'main', exceptions and RTTI by default.
Previously it was one of the most non-compliant where even trivial
standard-conforming code would not compile, stranding a large fraction of
C++ practitioners in the la-la land of an undocumented ad-hoc company
standard.
So, you are suggesting Sutter and Lippman are leading them from darkness
into the Light?
--
p->m == (*p).m == p[0].m http://www.kdevelop.org http://www.suse.com http://www.mozilla.org
"Steven T. Hatton" <su******@setid ava.kushan.aa> wrote in message
news:ea******** ************@sp eakeasy.net... Pete Vilder mentioned this a few days back. This is the "Compiler-Firewall
Idiom", or pimple. It's similar to an approach taken in some Java
designs. AAMOF, when I saw it in Java, my first reaction was "Oh by Þor! It's
freakin' headers all over again!"
My greatest misgiving about the approach is that it seems overly
complicated. I /feel/ as if there is a better more 'conventional' way of
dealing with the separation of interface and implementation.
Well come on then - bless us all with your insight.
I don't see how there can logically be a "better more 'conventional' way"
since this IS
the conventional way.
OTOH, it's
clear to me that the people who have advocated it are not stupid.*
Here's the discussion: http://www.gotw.ca/publications/mill05.htm
What do you make of it?
*(Sutter does serve the Dark Lord, but that's a different story. Lippman,
too has passed into darkness.)
--
p->m == (*p).m == p[0].m
http://www.kdevelop.org
http://www.suse.com
http://www.mozilla.org
"Steven T. Hatton" <su******@setid ava.kushan.aa> wrote in message
news:ea******** ************@sp eakeasy.net... Pete Vilder mentioned this a few days back. This is the "Compiler-Firewall
Idiom", or pimple. It's similar to an approach taken in some Java
designs. AAMOF, when I saw it in Java, my first reaction was "Oh by Þor! It's
freakin' headers all over again!"
My greatest misgiving about the approach is that it seems overly
complicated. I /feel/ as if there is a better more 'conventional' way of
dealing with the separation of interface and implementation.
Well come on then - bless us all with your insight.
I don't see how there can logically be a "better more 'conventional' way"
since this IS
the conventional way.
OTOH, it's
clear to me that the people who have advocated it are not stupid.*
Here's the discussion: http://www.gotw.ca/publications/mill05.htm
What do you make of it?
*(Sutter does serve the Dark Lord, but that's a different story. Lippman,
too has passed into darkness.)
--
p->m == (*p).m == p[0].m
http://www.kdevelop.org
http://www.suse.com
http://www.mozilla.org
Nick Hounsome wrote:
"Steven T. Hatton" <su******@setid ava.kushan.aa> wrote in message
news:ea******** ************@sp eakeasy.net... Pete Vilder mentioned this a few days back. This is the
"Compiler-Firewall
Idiom", or pimple. It's similar to an approach taken in some Java
designs. AAMOF, when I saw it in Java, my first reaction was "Oh by Þor! It's
freakin' headers all over again!"
My greatest misgiving about the approach is that it seems overly
complicated. I /feel/ as if there is a better more 'conventional' way of
dealing with the separation of interface and implementation.
Well come on then - bless us all with your insight.
I don't see how there can logically be a "better more 'conventional' way"
since this IS the conventional way.
You may notice I have '/feel/' emphasized, and ''conventional' ' in single
quotes. The intent of the former was to stress that I do not have
a /reasoned/ alternative. The intent of the latter was that I didn't
really mean the CFI (Compiler Firewall Idiom) is unconventional.
What do you see as the motive for it? Do you use it ubiquitously? I'll have
to start examining the headers in some of the programs I have the source
for to see if and how it is used there.
--
STH
Hatton's Law: "There is only One inviolable Law"
KDevelop: http://www.kdevelop.org SuSE: http://www.suse.com
Mozilla: http://www.mozilla.org
Nick Hounsome wrote:
"Steven T. Hatton" <su******@setid ava.kushan.aa> wrote in message
news:ea******** ************@sp eakeasy.net... Pete Vilder mentioned this a few days back. This is the
"Compiler-Firewall
Idiom", or pimple. It's similar to an approach taken in some Java
designs. AAMOF, when I saw it in Java, my first reaction was "Oh by Þor! It's
freakin' headers all over again!"
My greatest misgiving about the approach is that it seems overly
complicated. I /feel/ as if there is a better more 'conventional' way of
dealing with the separation of interface and implementation.
Well come on then - bless us all with your insight.
I don't see how there can logically be a "better more 'conventional' way"
since this IS the conventional way.
You may notice I have '/feel/' emphasized, and ''conventional' ' in single
quotes. The intent of the former was to stress that I do not have
a /reasoned/ alternative. The intent of the latter was that I didn't
really mean the CFI (Compiler Firewall Idiom) is unconventional.
What do you see as the motive for it? Do you use it ubiquitously? I'll have
to start examining the headers in some of the programs I have the source
for to see if and how it is used there.
--
STH
Hatton's Law: "There is only One inviolable Law"
KDevelop: http://www.kdevelop.org SuSE: http://www.suse.com
Mozilla: http://www.mozilla.org
Steven T. Hatton wrote: Pete Vilder mentioned this a few days back. This is the "Compiler-Firewall
Idiom", or pimple. It's similar to an approach taken in some Java
designs. AAMOF, when I saw it in Java, my first reaction was "Oh by Þor! It's
freakin' headers all over again!"
My greatest misgiving about the approach is that it seems overly
complicated. I /feel/ as if there is a better more 'conventional' way of
dealing with the separation of interface and implementation. OTOH, it's
clear to me that the people who have advocated it are not stupid.*
"Pimpl" is an idiom that one refactors into existing code to compile faster.
Refactors change design while leaving behavior the same. The Pimpl refactor
leaves logical design the same while tweaking physical design, so
translation units needn't see the details of other classes. That prevents
excessive recompiles when you change a highly reused class.
But Pimpl is for emergencies, after a design is committed. C++ was designed
to permit compilation firewalls based on abstract types; Pimpl abstracts a
concrete type.
Robert C. Martin's "Dependency Inversion Principle" describes this design
goal. http://www.objectmentor.com/resources/articles/dip.pdf
It implies that only classes with a few pure-virtual methods should be
widely re-used. This is both a valid design technique and a system that, in
C++, prevents runaway re-compiles.
--
Phlip http://www.xpsd.org/cgi-bin/wiki?Tes...UserInterfaces This thread has been closed and replies have been disabled. Please start a new discussion. Similar topics | |
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freakin' headers all over again!"
My greatest misgiving about the approach is that it seems overly
complicated. I /feel/ as if there is a better more 'conventional' way of
dealing with the separation of interface and...
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