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digitalmars.D.learn - Impishly stupid template question

reply Jeremy Gibson <jtgibson telus net> <Jeremy_member pathlink.com> writes:
I have a medium-weight queue class which I created some time in November or
December for general use, but never actually went ahead and tried using it until
now.  The queue class is a class template.

In C++, it's possible to create a member variable of template class: for
instance, "vector<int> coordinates", "vector<ObjectClass*> objectTable", etc.

In D, what is the equivalent?  I tried using "queue!(ac_event) event_queue" as a
member variable, but I'm getting compile errors:

alliance.d(74): class queue.queue(var_type) is used as a type
alliance.d(74): variable alliance.alliance.ac_game.event_queue voids have no val
ue

I know that templates in D have to be instantiated to be of use, so I'm
wondering how I can tell D that I want the event_queue variable to indicate an
instantiated queue of ac_event objects... what type do I need to assign to the
member variable, etc.?
Jun 20 2006
parent reply John Demme <me teqdruid.com> writes:
Jeremy Gibson wrote:


 I have a medium-weight queue class which I created some time in November
 or December for general use, but never actually went ahead and tried using
 it until
 now.  The queue class is a class template.
 
 In C++, it's possible to create a member variable of template class: for
 instance, "vector<int> coordinates", "vector<ObjectClass*> objectTable",
 etc.
 
 In D, what is the equivalent?  I tried using "queue!(ac_event)
 event_queue" as a member variable, but I'm getting compile errors:
 
 alliance.d(74): class queue.queue(var_type) is used as a type
 alliance.d(74): variable alliance.alliance.ac_game.event_queue voids have
 no val ue
 
 I know that templates in D have to be instantiated to be of use, so I'm
 wondering how I can tell D that I want the event_queue variable to
 indicate an instantiated queue of ac_event objects... what type do I need
 to assign to the member variable, etc.?


Unfortunately, DMD's template error messages suck it big-time.  I assume
that you're trying to do something similar to:
class CT(A) {
        A a;
}

class Y {
        CT!(Y) cty;
}

void main() {
}

That example compiles.  The error message you got appears whenever there's
_any_ issue with the template.  Chances are something else is up- look for
other error messages.  I've found that in any D program with templates,
only the first one or two error messages are worth anything.

Hope that helps!

-- 
~John Demme
me teqdruid.com
http://www.teqdruid.com/
Jun 20 2006
parent reply Jeremy Gibson <jtgibson telus net> <Jeremy_member pathlink.com> writes:
That example compiles.  The error message you got appears whenever there's
_any_ issue with the template.  Chances are something else is up- look for
other error messages.  I've found that in any D program with templates,
only the first one or two error messages are worth anything.


Those are the only error messages I'm getting, unfortunately, but I'll see
what's what in the queue module.  Sleep is more appealing than debugging right
now, so I'll have to look into it in the morning... =)
Jun 20 2006
parent Jeremy Gibson <jtgibson telus net> <Jeremy_member pathlink.com> writes:
In article <e7apdv$1kkd$1 digitaldaemon.com>, Jeremy Gibson <jtgibson telus net>
says...

That example compiles.  The error message you got appears whenever there's
_any_ issue with the template.  Chances are something else is up- look for
other error messages.  I've found that in any D program with templates,
only the first one or two error messages are worth anything.


Those are the only error messages I'm getting, unfortunately, but I'll see
what's what in the queue module.  Sleep is more appealing than debugging right
now, so I'll have to look into it in the morning... =)


After further testing, using /+ +/ comments to block out the ENTIRE contents of
the queue class, as well as removing all derived classes (stacks and pools) from
the queue module, I still suffered from these errors:

alliance.d(74): template instance queue is not a template declaration, it is a i
mport
alliance.d(74): queue!(ac_event) is used as a type
alliance.d(74): variable alliance.alliance.ac_game.event_queue voids have no val
ue

The problem, as the cryptic error message hinted at, was a name conflict between
the module "queue" and the class template name "queue".  I wanted to keep the
queue as a portable module for use in my other projects, but went ahead and
renamed the queue class to "ac_queue" for consistency with my other classes in
the project -- not surprisingly, everything then compiled perfectly (working
perfectly is another matter... I still have to write a test suite!).

I'll have to think up of a good alternate name for the module and/or class when
I add it to my code library.
Jun 21 2006