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mdlinux7@yahoo.co.in
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 Posted: Mon Oct 10, 2005 10:24 am Post subject: Lazy copy Semantics |
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Hi Experts,
Is it possible to enforce compiler to invoke lazy copy semantics
automatically when left object is constant ?
Suppose I need to write class MyString and I want that lazy copy
semantic should be used for following function :
void strlength(const MyString s_);
But for those functions which modifies an object should get their own
object without impacting right hand side object.
What operator needs to be implemented if I want that if u declare the
pass-by-value parameter as const, a new memory allocation should not
occur and the same memory location should be used to optimize the code.
Regards
Dinesh
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Risto Lankinen
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| Posted: Mon Oct 10, 2005 11:14 am Post subject: Re: Lazy copy Semantics |
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<mdlinux7 (AT) yahoo (DOT) co.in> wrote
| Quote: |
What operator needs to be implemented if I want that if u declare the
pass-by-value parameter as const, a new memory allocation should not
occur and the same memory location should be used to optimize the code.
|
To reply your question: C++ does not have const
constructors. Therefore, it is not possible to have
separate constructors for const and non-const object.
To offer a solution to your problem: Pass any const
parameter as a reference instead of value.
- Risto -
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mdlinux7@yahoo.co.in
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| Posted: Mon Oct 10, 2005 8:02 pm Post subject: Re: Lazy copy Semantics |
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Thanks for your reply. I asked this question because i was little
confused when I read Gotw#81 [constant optimization] which states below
lines
If so, and if you happen to use the smartened-up operator[ ]() or
iterators, and you declare the pass-by-value parameter as const, then
-- wonder of wonders! -- the String can, with no further help from you,
automagically and wholesomely optimize your code by avoiding a deep
copy...
That's why I was looking for a way to enforce compiler to use lazy
copying if you declare pass-by-value parameter as const.
Regards
Dinesh
[ See http://www.gotw.ca/resources/clcm.htm for info about ]
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Francis Glassborow
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| Posted: Thu Oct 13, 2005 10:59 pm Post subject: Re: Lazy copy Semantics |
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In article <Upr2f.11186$Nb2.196751 (AT) news1 (DOT) nokia.com>, Risto Lankinen
<rlankine (AT) hotmail (DOT) com> writes
| Quote: | To reply your question: C++ does not have const
constructors. Therefore, it is not possible to have
separate constructors for const and non-const object.
|
At least not yet but there is a proposal to add them to the next C++
Standard.
--
Francis Glassborow ACCU
Author of 'You Can Do It!' see http://www.spellen.org/youcandoit
For project ideas and contributions: http://www.spellen.org/youcandoit/projects
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Axter
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| Posted: Fri Oct 14, 2005 5:35 pm Post subject: Re: Lazy copy Semantics |
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[email]mdlinux7 (AT) yahoo (DOT) co.in[/email] wrote:
| Quote: | Thanks for your reply. I asked this question because i was little
confused when I read Gotw#81 [constant optimization] which states below
lines
If so, and if you happen to use the smartened-up operator[ ]() or
iterators, and you declare the pass-by-value parameter as const, then
-- wonder of wonders! -- the String can, with no further help from you,
automagically and wholesomely optimize your code by avoiding a deep
copy...
That's why I was looking for a way to enforce compiler to use lazy
copying if you declare pass-by-value parameter as const.
|
You could try using a COW (Copy On Write) smart pointer.
Check out the following class:
http://code.axter.com/cow_ptr.h
You can pass by value the above smart pointer, and it will do reference
counting untill an attempt is made to access the pointer.
[ See http://www.gotw.ca/resources/clcm.htm for info about ]
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