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* Re: c++/9865: [3.2/3.3/3.4 regression] Template matching for reference types
@ 2003-03-27 14:04 nathan
0 siblings, 0 replies; 4+ messages in thread
From: nathan @ 2003-03-27 14:04 UTC (permalink / raw)
To: dbeck, gcc-bugs, gcc-prs, nathan
Synopsis: [3.2/3.3/3.4 regression] Template matching for reference types
State-Changed-From-To: analyzed->closed
State-Changed-By: nathan
State-Changed-When: Thu Mar 27 14:01:43 2003
State-Changed-Why:
Not a bug. It is doing exactly what the standard says.
template <typename T> struct Foo; //#1
template <typename T> struct Foo<const T>; //#2
Foo<short &> ;;// #1 or #2?
14.5.4.1/2 says a partial specialization matches if the template arguments of the partial specialization can be deduced from the actual template argument list. So, can 'const T' deduce a T from 'short &'? One deduction is that T is 'short &', which leads to a const qualified reference type. [8.3.2]/1 says that that's ill-formed *except* when
the cv qualifiers are introduced through the use of a typedef or of a template type argument, in which case they are ignored. So the partial specialization #2 is selected, rather than the primary template #1.
That is PR 2645.
DR295 was the similar case for function types, and I think it is bad for exactly the same reasons PR 9865 is giving a surprise.
To avoid the surprise, you need another partial specialization
template <typename T> struct foo<T &>;
http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=9865
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: c++/9865: [3.2/3.3/3.4 regression] Template matching for reference types
@ 2003-03-06 20:57 jason
0 siblings, 0 replies; 4+ messages in thread
From: jason @ 2003-03-06 20:57 UTC (permalink / raw)
To: dbeck, gcc-bugs, gcc-prs, jason, nathan
Synopsis: [3.2/3.3/3.4 regression] Template matching for reference types
Responsible-Changed-From-To: jason->nathan
Responsible-Changed-By: jason
Responsible-Changed-When: Thu Mar 6 20:57:50 2003
Responsible-Changed-Why:
This was broken by your patch of a year ago for c++/2645 and DR 295.
http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=9865
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: c++/9865: [3.2/3.3/3.4 regression] Template matching for reference types
@ 2003-03-06 18:04 jason
0 siblings, 0 replies; 4+ messages in thread
From: jason @ 2003-03-06 18:04 UTC (permalink / raw)
To: dbeck, gcc-bugs, gcc-prs, jason, nobody
Synopsis: [3.2/3.3/3.4 regression] Template matching for reference types
Responsible-Changed-From-To: unassigned->jason
Responsible-Changed-By: jason
Responsible-Changed-When: Thu Mar 6 18:04:41 2003
Responsible-Changed-Why:
got it
http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=9865
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: c++/9865: [3.2/3.3/3.4 regression] Template matching for reference types
@ 2003-02-26 17:52 bangerth
0 siblings, 0 replies; 4+ messages in thread
From: bangerth @ 2003-02-26 17:52 UTC (permalink / raw)
To: dbeck, gcc-bugs, gcc-prs, nobody
Old Synopsis: traits for const types have bad results
New Synopsis: [3.2/3.3/3.4 regression] Template matching for reference types
State-Changed-From-To: open->analyzed
State-Changed-By: bangerth
State-Changed-When: Wed Feb 26 17:52:32 2003
State-Changed-Why:
Confirmed. A shorter testcase is this:
----------------------------
template <typename T> struct is_const {
static const bool value = false;
};
template <typename T> struct is_const<const T> {
};
int main() {
is_const<short &>::value;
}
-------------------------
I don't think it should fail to compile, but it does since
3.2, the reason being that gcc decides to look into the
const specialization of the template.
W.
http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=9865
^ permalink raw reply [flat|nested] 4+ messages in thread
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2003-03-27 14:04 c++/9865: [3.2/3.3/3.4 regression] Template matching for reference types nathan
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2003-03-06 20:57 jason
2003-03-06 18:04 jason
2003-02-26 17:52 bangerth
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