specializing std::less

[Exits Funnel]

I've got this code:

//Begin foo.cpp
#include <utility>
#include <bits/stl_function.h>

typedef std:air<int, int> int_pair_t;

template<>
struct std::less<int_pair_t> { };
//End foo.cpp

g++ has this to say on the issue:

foo.cpp:7: specializing `struct std::less<int_pair_t>' in different
namespace
/usr/include/c++/3.2.3/bits/stl_function.h:195: from definition of `
template<class _Tp> struct std::less'

This seems reasonable (though for what it's worth, it compiles under
VC7.1). I can fix the problem by wrapping the specialization in a
'namespace std' block but I'm wondering if this is prudent or is there
some other solution. Thanks.

-exits

 

[Victor Bazarov]

[...] I can fix the problem by wrapping the specialization in a
'namespace std' block but I'm wondering if this is prudent or is there
some other solution. Thanks.

It's expressly allowed by the Standard.

Victor

 

[Sharad Kala]

I've got this code:
[snip]

This seems reasonable (though for what it's worth, it compiles under
VC7.1). I can fix the problem by wrapping the specialization in a
'namespace std' block but I'm wondering if this is prudent or is there
some other solution. Thanks.

That's fine (Read 17.4.3.1/1)

Sharad

 

[Dietmar Kuehl]

[...] I can fix the problem by wrapping the specialization in a
'namespace std' block but I'm wondering if this is prudent or is there
some other solution. Thanks.

It's expressly allowed by the Standard.

It is allowed to [partially] specialize class templates from the
standard library in namespace 'std' *IF* the specialization involves
a user defined type. 'std:air<int, int>' as used in the original
article does not qualify for a user defined specialization!

That said, it is probably save to specialize things which don't exist
according to the standard - only there is no guarantee that it indeed
works...

 

[Sharad Kala]

[...] I can fix the problem by wrapping the specialization in a
'namespace std' block but I'm wondering if this is prudent or is there
some other solution. Thanks.

It's expressly allowed by the Standard.

It is allowed to [partially] specialize class templates from the
standard library in namespace 'std' *IF* the specialization involves
a user defined type. 'std:air<int, int>' as used in the original
article does not qualify for a user defined specialization!

True, but this is a well known work around that works on all the modern
compilers I have tested it on. But as you say it is not legal as quoted in
the Standard. Is there a proposal to change it (for std:air) ?

Sharad

 

[Exits Funnel]

[...] I can fix the problem by wrapping the specialization in a
'namespace std' block but I'm wondering if this is prudent or is
there

some other solution. Thanks.

It's expressly allowed by the Standard.

It is allowed to [partially] specialize class templates from the
standard library in namespace 'std' *IF* the specialization involves
a user defined type. 'std:air<int, int>' as used in the original
article does not qualify for a user defined specialization!

True, but this is a well known work around that works on all the modern
compilers I have tested it on. But as you say it is not legal as quoted in
the Standard. Is there a proposal to change it (for std:air) ?

Sharad

Thanks Victor, Sharad, Dietmar. I appreciate the information.

-exits