Hi,
I remember from somewhere reading that inlining constructors is a
'BadThing', but now can't seem to find the original source. I can't
however thing of a reason why it would be for simple constructors...
any thoughts
Mike
21  2055 
On May 24, 1:52 pm, Michael Hull <mikehul...@goo glemail.comwrot e:
Hi,
I remember from somewhere reading that inlining constructors is a
'BadThing', but now can't seem to find the original source. I can't
however thing of a reason why it would be for simple constructors...
any thoughts
Mike
Hi,
For simple constructors of classes having implicit data types as their
data members only it is ok to have inline constructors but even it is
not getting derived.
But for heavy classes (classes with many user defined data types as
data members) inlining constructors is a bad thing and it becomes even
more worse if the class is inherited from some other class.
When you will look at the number of lines in the constructor you will
feel it should be allowed, but an object construction results in
calling so many constructor calls (of all composed objects and of all
base classes and their composed objects).
Please correct me if i am wrong.
Vineet
Vineet Chawla wrote :
On May 24, 1:52 pm, Michael Hull <mikehul...@goo glemail.comwrot e:
>Hi,
I remember from somewhere reading that inlining constructors is a
'BadThing', but now can't seem to find the original source. I can't
however thing of a reason why it would be for simple constructors...
any thoughts
Mike
Hi,
For simple constructors of classes having implicit data types as their
data members only it is ok to have inline constructors but even it is
not getting derived.
But for heavy classes (classes with many user defined data types as
data members) inlining constructors is a bad thing and it becomes even
more worse if the class is inherited from some other class.
When you will look at the number of lines in the constructor you will
feel it should be allowed, but an object construction results in
calling so many constructor calls (of all composed objects and of all
base classes and their composed objects).
You're describing WHEN it is bad, but not WHY it is bad, so this is not
helping. I can think of several reasons: inlining large functions
causes massive code bloat, thus increasing the size of your executable
and probably decreasing performance. Another reason might be that the
larger the constructor is, the more dependencies (on average) it has on
the rest of the code, causing you to rebuild large parts of your
application for even small changes that don't have to do anything with
the users of the constructor in question.
However, these reasons all apply to regular functions as well, and the
threadstarter was explicitely talking about constructors. Besides that,
keep in mind that 'inline' is only a hint to the compiler - a good
compiler will make his own judgements on whether to inline a function
or not, no matter if the constructor/function was actually defined as
being inline, so the first argument is pretty moot.
So to conclude, I have no idea why inlining constructors in particular
is a Bad Thing.
- Sylvester
Sylvester Hesp wrote:
Besides that,
keep in mind that 'inline' is only a hint to the compiler
It's not *only* a hint. It does more than that (specifically
related to linking).
Juha Nieminen wrote:
Sylvester Hesp wrote:
>Besides that,
keep in mind that 'inline' is only a hint to the compiler
It's not *only* a hint. It does more than that (specifically
related to linking).
Yes I might've been a bit unclear. I wasn't talking about the inline
keyword in general, I was talking about the actual process of function
inlining by the compiler.
- Sylvester
On May 25, 4:07 am, Sylvester Hesp <s.hes...@SPAMo isyn.nlwrote:
Juha Nieminen wrote:
Sylvester Hesp wrote:
Besides that,
keep in mind that 'inline' is only a hint to the compiler
It's not *only* a hint. It does more than that (specifically
related to linking).
Yes I might've been a bit unclear. I wasn't talking about the inline
keyword in general, I was talking about the actual process of function
inlining by the compiler.
- Sylvester
If you see the third paragraph in my reply there i have mentioned why
it is bad.
When you will look at the number of lines in the constructor you will
feel it should be allowed, but an object construction results in
calling so many constructor calls (of all composed objects and of all
base classes and their composed objects).
Yes i agree with your point that it is just a hint to the compiler. I
don't know if there is some other reason as well for this.
Regards
Vineet
Vineet Chawla wrote:
On May 25, 4:07 am, Sylvester Hesp <s.hes...@SPAMo isyn.nlwrote:
>Juha Nieminen wrote:
>>Sylvester Hesp wrote:
Besides that,
keep in mind that 'inline' is only a hint to the compiler
It's not *only* a hint. It does more than that (specifically
related to linking).
Yes I might've been a bit unclear. I wasn't talking about the inline
keyword in general, I was talking about the actual process of function
inlining by the compiler.
- Sylvester
If you see the third paragraph in my reply there i have mentioned why
it is bad.
>> When you will look at the number of lines in the constructor you will
feel it should be allowed, but an object construction results in
calling so many constructor calls (of all composed objects and of all
base classes and their composed objects).
Yes i agree with your point that it is just a hint to the compiler. I
don't know if there is some other reason as well for this.
Regards
Vineet
The fact that you write a method, function or constructor inline does
*NOT* force the compiler to inline the code and cause 'massive code
bloat'. I would be very disappointed in such a stupid compiler.
People get so confused about inlining. As Juha said the meaning of
inline is to tell the compiler not to apply the 'one definition rule',
i.e. it means it's OK to put the function definition in a header file.
Whether it's a good idea to do this or not is primarily a style issue.
Whether a function's code is inlined is an optmization issue, and I
would exect a good compiler not to inline some functions I had declared
inline, and also to inline some functions I had not declared inline.
Both of these things are optmizations which the compiler can work out
for itself. VC++ 2005 does this.
john
On May 25, 8:12 am, John Harrison <john_androni.. .@hotmail.comwr ote:
Vineet Chawla wrote:
On May 25, 4:07 am, Sylvester Hesp <s.hes...@SPAMo isyn.nlwrote:
Juha Nieminen wrote:
Sylvester Hesp wrote:
Besides that,
keep in mind that 'inline' is only a hint to the compiler
It's not *only* a hint. It does more than that (specifically
related to linking).
Yes I might've been a bit unclear. I wasn't talking about the inline
keyword in general, I was talking about the actual process of function
inliningby the compiler.
- Sylvester
If you see the third paragraph in my reply there i have mentioned why
it is bad.
> When you will look at the number of lines in the constructor you will
feel it should be allowed, but an object construction results in
calling so many constructor calls (of all composed objects and of all
base classes and their composed objects).
Yes i agree with your point that it is just a hint to the compiler. I
don't know if there is some other reason as well for this.
Regards
Vineet
The fact that you write a method, function or constructor inline does
*NOT* force the compiler to inline the code and cause 'massive code
bloat'. I would be very disappointed in such a stupid compiler.
People get so confused aboutinlining. As Juha said the meaning of
inline is to tell the compiler not to apply the 'one definition rule',
i.e. it means it's OK to put the function definition in a header file.
Whether it's a good idea to do this or not is primarily a style issue.
Whether a function's code is inlined is an optmization issue, and I
would exect a good compiler not to inline some functions I had declared
inline, and also to inline some functions I had not declared inline.
Both of these things are optmizations which the compiler can work out
for itself. VC++ 2005 does this.
john
Thanks for all the replies..... most of this is covered in the FAQ, i
was wondering whether the Constructor is a special case in particular,
i.e, If I have a simple, POD class, is there a reason not to inline
the constructor (except the standard reasons of not inlining...) ?
Thanks for the replies
Mike
On May 25, 9:55 am, Michael Hull <mikehul...@goo glemail.comwrot e:
[...]
Thanks for all the replies..... most of this is covered in the FAQ, i
was wondering whether the Constructor is a special case in particular,
i.e, If I have a simple, POD class, is there a reason not to inline
the constructor (except the standard reasons of not inlining...) ?
The main reason for the special rule concerning constructors
(and destructors) is that even if the function looks trivial, it
might not be, which is not normally the case for other
functions. At least one place I worked (a long time ago) did
have a rule in the coding guidelines against inlining
constructors and destructors.
Several things have changed since then. Projects have become
larger (so dependency management becomes more important),
function calls faster, and the most frequent general rule today
is not to inline anything until the profiler says to do so. On
the other hand, templates in the absense of export means that
the dependencies are there anyway, so some guidelines are more
liberal with regards to inlining template functions (where they
allow templates).
--
James Kanze (GABI Software) email:ja******* **@gmail.com
Conseils en informatique orientée objet/
Beratung in objektorientier ter Datenverarbeitu ng
9 place Sémard, 78210 St.-Cyr-l'École, France, +33 (0)1 30 23 00 34
James Kanze wrote:
On May 25, 9:55 am, Michael Hull <mikehul...@goo glemail.comwrot e:
[...]
>Thanks for all the replies..... most of this is covered in the FAQ, i
was wondering whether the Constructor is a special case in particular,
i.e, If I have a simple, POD class, is there a reason not to inline
the constructor (except the standard reasons of not inlining...) ?
The main reason for the special rule concerning constructors
(and destructors) is that even if the function looks trivial, it
might not be, which is not normally the case for other
functions. At least one place I worked (a long time ago) did
have a rule in the coding guidelines against inlining
constructors and destructors.
Just out of interest, what did those guidelines say about simple
aggregates containing lots of members that have no trivial
constructors?
struct Foo
{
Type1 a;
Type2 b;
Type3 c;
// etc.
};
It has no defined default constructor, so one is generated. But the
generated constructor can be very expensive, and you have no control
over whether it gets inlined. Did those guidelines said you should
define a non-inlined constructor to circumvent compiler inlining?
- Sylvester This thread has been closed and replies have been disabled. Please start a new discussion. Similar topics | |
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