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Effective C++: Item 26
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Bart Vandewoestyne
Sep 20, 2012, 11:02:00 AM9/20/12
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I am trying to reproduce the ambiguity problem from the first example in Item 26 from Scott Meyers' book 'Effective C++'. My code is online at
https://github.com/BartVandewoestyne/cpp/blob/master/books/Effective_C%2B%2B/item26/potential_ambiguity.cpp
In the book, no definition of A's copy constructor nor B's operator A() is given, so i defined it myself... hopefully correct somehow...
Compiling this code with g++ 4.6.2 and the -Wall option succeeds without errors and when I run it, i get:
A(const B&)
f(const A&)
so apparently A's copy constructor gets called and there's no ambiguity problem.
I was suspecting am ambiguity problem at compile time... what am I doing/interpreting wrong?
Regards,
Bart
https://github.com/BartVandewoestyne/cpp/blob/master/books/Effective_C%2B%2B/item26/potential_ambiguity.cpp
In the book, no definition of A's copy constructor nor B's operator A() is given, so i defined it myself... hopefully correct somehow...
Compiling this code with g++ 4.6.2 and the -Wall option succeeds without errors and when I run it, i get:
A(const B&)
f(const A&)
so apparently A's copy constructor gets called and there's no ambiguity problem.
I was suspecting am ambiguity problem at compile time... what am I doing/interpreting wrong?
Regards,
Bart
Victor Bazarov
Sep 20, 2012, 2:40:23 PM9/20/12
to
exactly where you expected it.
V
--
I do not respond to top-posted replies, please don't ask
Bart Vandewoestyne
Sep 20, 2012, 3:45:33 PM9/20/12
to
On Thursday, September 20, 2012 8:41:14 PM UTC+2, Victor Bazarov wrote:
>
> Not sure about the compiler you used. Comeau online gives an error
> exactly where you expected it.
I now tested with g++ (Ubuntu/Linaro 4.6.3-1ubuntu5) 4.6.3 and everything compiles _without_ any ambiguity error...
>
> Not sure about the compiler you used. Comeau online gives an error
> exactly where you expected it.
Who's wrong here? The book or the compiler?
Regards,
Bart
Victor Bazarov
Sep 20, 2012, 6:49:30 PM9/20/12
to
online, VC++ 2010, VC++ 2012) report an error...
ptyxs
Sep 21, 2012, 7:14:56 AM9/21/12
to Bart Vandewoestyne
variable definitions as long as possible".
Please tell what edition you are using and what is the title of the item
you are discussing.
Thanks.
Ptyxs
Nobody
Sep 21, 2012, 8:05:14 AM9/21/12
to
On Fri, 21 Sep 2012 13:14:56 +0200, ptyxs wrote:
> In my Effective C++ THIRD EDITION, Item 26 is entitled : "Postpone
> variable definitions as long as possible".
>
> Please tell what edition you are using and what is the title of the item
> you are discussing.
I'm fairly sure that it's the second edition, where item 26 is titled
> In my Effective C++ THIRD EDITION, Item 26 is entitled : "Postpone
> variable definitions as long as possible".
>
> Please tell what edition you are using and what is the title of the item
> you are discussing.
"Guard against potential ambiguity".
Richard Delorme
Sep 21, 2012, 8:19:51 AM9/21/12
to
Le 20/09/2012 17:02, Bart Vandewoestyne a écrit :
--
Richard
Scott Lurndal
Sep 21, 2012, 9:55:13 AM9/21/12
to
$ g++ -pedantic -o /tmp/a /tmp/a.cpp
/tmp/a.cpp: In function 'int main()':
/tmp/a.cpp:39: error: conversion from 'B' to 'const A' is ambiguous
/tmp/a.cpp:22: note: candidates are: B::operator A() const
/tmp/a.cpp:13: note: A::A(const B&)
$
Bart Vandewoestyne
Sep 21, 2012, 10:47:49 AM9/21/12
to
On Friday, September 21, 2012 2:05:03 PM UTC+2, Nobody wrote:
>
> I'm fairly sure that it's the second edition, where item 26 is titled
> "Guard against potential ambiguity".
Indeed.
>
> I'm fairly sure that it's the second edition, where item 26 is titled
> "Guard against potential ambiguity".
Regards,
Bart
Bart Vandewoestyne
Sep 21, 2012, 10:51:29 AM9/21/12
to
On Friday, September 21, 2012 2:19:52 PM UTC+2, Richard Delorme wrote:
>
> Try to compile your code with the -pedantic options.
Indeed! That gives me the ambiguity error!
>
> Try to compile your code with the -pedantic options.
Thanks!
Bart
Jorgen Grahn
Sep 22, 2012, 4:19:49 AM9/22/12
to
several other warning options) with g++. Lots of things which end up
as questions here (often much more trivial than this) would have been
caught that way.
/Jorgen
--
// Jorgen Grahn <grahn@ Oo o. . .
\X/ snipabacken.se> O o .
ptyxs
Sep 24, 2012, 10:59:45 AM9/24/12
to Nobody
Appendix B, Item Mapping Between Second and Third Edition shows that
there is no mapping from second edition item 26 to any third edition item.
Would that suggest that the author, as an afterthought, considered that
second edition item 26 was somehow inaccurate or useless ??
Ptyxs
ptyxs
Sep 24, 2012, 11:02:09 AM9/24/12
to Bart Vandewoestyne
Bart Vandewoestyne
Sep 25, 2012, 5:04:26 AM9/25/12
to
On Saturday, September 22, 2012 10:19:50 AM UTC+2, Jorgen Grahn wrote:
>
> I've said it before, but I recommend always using -pedantic (and
> several other warning options) with g++. Lots of things which end up
> as questions here (often much more trivial than this) would have been
> caught that way.
It's nice to know that the ambiguity error pops up in pedantic mode. I have emailed Scott Meyers about this, and now both him and me are actually puzzled why it *only* pops up in pedantic mode... Shouldn't that ambiguity error pop up without the -pedantic option too?
>
> I've said it before, but I recommend always using -pedantic (and
> several other warning options) with g++. Lots of things which end up
> as questions here (often much more trivial than this) would have been
> caught that way.
Regards,
Bart
Nobody
Sep 26, 2012, 6:23:02 PM9/26/12
to
On Tue, 25 Sep 2012 02:04:26 -0700, Bart Vandewoestyne wrote:
> It's nice to know that the ambiguity error pops up in pedantic mode. I
> have emailed Scott Meyers about this, and now both him and me are
> actually puzzled why it *only* pops up in pedantic mode... Shouldn't
> that ambiguity error pop up without the -pedantic option too?
Without -pedantic, gcc extensions are still enabled so long as they do not
> It's nice to know that the ambiguity error pops up in pedantic mode. I
> have emailed Scott Meyers about this, and now both him and me are
> actually puzzled why it *only* pops up in pedantic mode... Shouldn't
> that ambiguity error pop up without the -pedantic option too?
affect the interpretation of valid code.
The -std= option should ensure that all valid code is interpreted as
specified by the standard. The -pedantic option is required if you
also want invalid code to be handled as specified by the standard (i.e.
generating any required diagnostics).
Balog Pal
Oct 5, 2012, 6:01:04 PM10/5/12
to
On 9/24/2012 5:02 PM, ptyxs wrote:
> One interesting thing to note is that in the THIRD EDITION, pp.278-279,
> Appendix B, Item Mapping Between Second and Third Edition shows that
> there is no mapping from second edition item 26 to any third edition item.
>
> Would that suggest that the author, as an afterthought, considered that
> second edition item 26 was somehow inaccurate or useless ??
No, just less important than the other items that made into the 3rd ed.
> One interesting thing to note is that in the THIRD EDITION, pp.278-279,
> Appendix B, Item Mapping Between Second and Third Edition shows that
> there is no mapping from second edition item 26 to any third edition item.
>
> Would that suggest that the author, as an afterthought, considered that
> second edition item 26 was somehow inaccurate or useless ??
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