I have a question about explicit instantiation. Is it possible to declare
class template or function template in one namespace and explicitly
instantiate it in another namespace?

Consider the following example:

namespace serialization {

=9A=9A=9A=9Atemplate<class=9AT>
=9A=9A=9A=9Aclass=9Ahelper=9A{};
=9A=9A=9A=9A
=9A=9A=9A=9Atemplate<class=9AT,=9Aclass=9ASeq>
=9A=9A=9A=9Avoid
=9A=9A=9A=9Aboost_template_instantiate(T=9A&,Seq=9A&)=9A{}
}

namespace X
{
=9A=9A=9A=9Aclass=9AC=9A{};
=9A=9A=9A=9A=9A=9A=9A=9A=9A=9A=9A=9A
=9A=9A=9A=9Atemplate
=9A=9A=9A=9Avoid
=9A=9A=9A=9Aserialization::boost_template_instantiate<>(X::C=9A&,=9Aint=9A=
&);
=9A=9A=9A=9A
=9A=9A=9A=9Atemplate
=9A=9A=9A=9Aclass=9Aserialization::helper<int>;
}

Both gcc 3.3 and online Comeau reject the first instantiation. The error
message say explicit instantiation can't be placed here. OTOH, explicit
instantiation of the class works OK. I can't find anything in the standar=
d
that would explain this error.=20

So, it it just the same bug in two compilers, or I've missed something?

Thanks in advance,
Volodya



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(to mods: this is a repost - I got a notification from my first post but
nothing further...)

>"Vladimir Prus" <ghost@cs.msu.su> wrote in message
news:u5boi1-7te.ln1@zigzag.lvk.cs.msu.su...

>I have a question about explicit instantiation. Is it possible to declare
>class template or function template in one namespace and explicitly
>instantiate it in another namespace?

I believe this should be valid - see Explicit instantiation 14.7.2p5

"An explicit instantiation of a class or function template specialization is
placed in the namespace in which
the template is defined."

(MSVC 7 compiles your example, FWIW)

Roger Orr
--
MVP in C++ at www.brainbench.com


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"Vladimir Prus" <ghost@cs.msu.su> skrev i meddelandet
news:u5boi1-7te.ln1@zigzag.lvk.cs.msu.su...

> I have a question about explicit instantiation. Is it possible to declare
> class template or function template in one namespace and explicitly
> instantiate it in another namespace?

I think this is covered in
http://std.dkuug.dk/jtc1/sc22/wg21/docs/cwg_defects.html#275

Proposed resolution : "An explicit instantiation shall appear in an
enclosing namespace of its template."

--
Dag Henriksson


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>"Vladimir Prus" <ghost@cs.msu.su> wrote in message
news:u5boi1-7te.ln1@zigzag.lvk.cs.msu.su...

>I have a question about explicit instantiation. Is it possible to declare
>class template or function template in one namespace and explicitly
>instantiate it in another namespace?

I believe this should be valid - see Explicit instantiation 14.7.2p5

"An explicit instantiation of a class or function template specialization is
placed in the namespace in which
the template is defined."

(MSVC 7 compiles your example, FWIW)

Roger Orr
--
MVP in C++ at www.brainbench.com


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