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Re: %union with STL
From: |
Vincent Zweije |
Subject: |
Re: %union with STL |
Date: |
Wed, 27 May 2009 10:32:20 +0200 |
User-agent: |
Mutt/1.5.18 (2008-05-17) |
On Tue, May 26, 2009 at 10:57:01PM +0200, Hans Aberg wrote:
|| On 26 May 2009, at 22:38, Luca wrote:
||
|| >> Checking what the compiler accepts is a good way to produce non-
|| >> standard source code
|| > using a pointer inside a union is a good way to produce non-standard
|| > source code?!?
||
|| So what does the C++ standard say about it?
"In a union, at most one of the data members can be active at any time,
that is, the value of at most one of the data members can be stored in
a union at any time. [...] Each data member is allocated as if it were
the sole member of a struct."
And for those interested in the problem with the bison union:
"An object of a class with a non-trivial constructor (12.1), a non-trivial
copy construtor (12.8), a non-trivial destructor (12.4), or a non-trivial
copy assignment operator (13.5.3, 12.8) cannot be a member of a union,
nor can an array of such objects."
The rationale being that when default-constructing, copy-constructing,
destroying, or assigning the union, the program doesn't have to know which
member to use, because under these rules it can just operate on the data.
In short, I see no problem with this union at all as bison uses it,
semantics-wise, but it is unfortunate that you cannot put your own
classes in there in general.
|| >> But in the end, I think the OP problem might be due to an older
|| >> version of Bison or an instantiation problem - lack of declaration
|| >> or a problem with the compiler.
|| > Simply some #include is missing...
||
|| Did you see the post by Vincent?
And I noticed that std::string appears to be used as well, which needs
a #include <string>. :)
Ciao. Vincent.
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- %union with STL, Paritosh Aggarwal, 2009/05/22
- Fwd: %union with STL, Paritosh Aggarwal, 2009/05/22
- Re: %union with STL, Tommy Nordgren, 2009/05/24
- Re: %union with STL, Luca, 2009/05/24
- Re: %union with STL, Tommy Nordgren, 2009/05/24
- Re: %union with STL, Hans Aberg, 2009/05/24
- Re: %union with STL, Luca, 2009/05/25
- Re: %union with STL, Hans Aberg, 2009/05/25
- Re: %union with STL, Luca, 2009/05/26
- Re: %union with STL, Hans Aberg, 2009/05/26
- Re: %union with STL,
Vincent Zweije <=
- Re: %union with STL, Hans Aberg, 2009/05/27
- Re: %union with STL, Akim Demaille, 2009/05/27
- Re: %union with STL, Hans Aberg, 2009/05/27
- Re: %union with STL, Hans Aberg, 2009/05/29
Re: %union with STL, Hans Aberg, 2009/05/24