 |
C++Talk.NET
C++ language newsgroups
|
| View previous topic :: View next topic |
| Author |
Message |
Chor Lit
Guest
|
 Posted: Wed Apr 19, 2006 5:06 pm Post subject: Linkage of templates |
 |
|
I read Nicolai and David's book "C++ templates" and they mention, on
page 99, that every template must have a name that is unique within its
scope. The following is the example they gave:
int C;
class C; //ok: class names & nonclass names are in a different
"space"
int X;
template < typename T>
class X; //Error:conflict with variable X
struct S;
template <typename T>
class S; //Error:conflict with struct S
Can anyone explain why does template names must be unique ? What is the
rationale behind this restriction imposed by the language ? Since int C
and class C can share the same name, I don't see why the name 'X' and
'S' above can raise any conflict.
Thanks.
---
[ comp.std.c++ is moderated. To submit articles, try just posting with ]
[ your news-reader. If that fails, use mailto:std-c++@ncar.ucar.edu ]
[ --- Please see the FAQ before posting. --- ]
[ FAQ: http://www.comeaucomputing.com/csc/faq.html ] |
|
| Back to top |
|
 |
Alberto Ganesh Barbati
Guest
|
| Posted: Thu Apr 20, 2006 2:06 am Post subject: Re: Linkage of templates |
|
|
Chor Lit ha scritto:
| Quote: |
int X;
template < typename T
class X; //Error:conflict with variable X
Can anyone explain why does template names must be unique ? What is the
rationale behind this restriction imposed by the language ? Since int C
and class C can share the same name, I don't see why the name 'X' and
'S' above can raise any conflict.
|
I think the restriction was introduced to simplify the parser, because
the use of the angular bracket can lead to ambiguities. Consider this:
template <int N> class X { operator int(); };
int X; // (1) illegal
int Y = X<0>(); // (2) ???
int Z = X<0; // (3) ???
If line (1) were legal, then the parser would have big problems in
parsing (2) and (3). In both cases the first three tokens "X<0" can be
interpreted either as a boolean expression (if X is the variable) or the
beginning of a template-id (if X is the template-name). Detecting which
case from the context requires the parser to perform some kind of
backtracking, thus adding extra complexity that is not worth the effort.
The other case:
| Quote: | struct S;
template <typename T
class S; //Error:conflict with struct S
|
is less obvious, I think it was introduced just for consistency and
because it's the Right Thing(tm). In fact I think that having a
(non-template) class and a variable with the same name is not good
programming style and it's tolerated only because of backward
compatibility and compatibility with C. Remember that in C the "struct"
in "struct C" cannot be omitted, so there is no ambiguity there.
Ganesh
---
[ comp.std.c++ is moderated. To submit articles, try just posting with ]
[ your news-reader. If that fails, use mailto:std-c++@ncar.ucar.edu ]
[ --- Please see the FAQ before posting. --- ]
[ FAQ: http://www.comeaucomputing.com/csc/faq.html ] |
|
| Back to top |
|
|
|
|
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
|
|
FAQ
Search
Memberlist
Usergroups
Register
Profile
Log in to check your private messages
Log in
