Templates: "implicit typename is deprecated" error and typedef'ing templates

  • Thread starter Generic Usenet Account
  • Start date
G

Generic Usenet Account

This is a two-part question.

(1) I have implemented a "Datastructure Registry" template class. I am
getting no compiler warnings with older compilers, but newer compilers
are generating the following error messages:
warning: implicit typename is deprecated,
please see the documentation for details

Can someone kindly suggest how to get rid of these warnings? The
source code follows.

(2) I want to use the "Datastructure Registry" template class to
implement a "Registry of Singletons", as mentioned in the GoF Design
patterns book. For this I want to do something like this:

typedefine the "Datastructure Registry" template-class as the "Registry
of Singletons" template-class.

I have tried various things, but nothing seems to be working.

typedef DSRegistry SingletonRegistry;
typedef DSRegistry<class T> SingletonRegistry<class T>;
typedef template DSRegistry<class T> template SingletonRegistry<class
T>;
typedef DSRegistry<class T> template SingletonRegistry<class T>;

Thanks,
Gus

//////////////////////////////////////////////////
#ifndef _DSREGISTRY_H_
#define _DSREGISTRY_H_

#include <iostream>
#include <string>
#include <map>

using namespace std;

template <class T>
class DSRegistry
{
public:
virtual ~DSRegistry(){};

static DSRegistry& instance()
{
if(_instance == NULL)
_instance = new DSRegistry();
return *_instance;
};

bool addEntry(string name, T* ptr)
{
bool retVal = false;

if(_map.find(name) == _map.end())
{
pair<string, T*> newEntry;
newEntry.first = name;
newEntry.second = ptr;
retVal = _map.insert(newEntry).second;
}

if(retVal == false)
{
#ifdef DEBUG
cerr << "Datastructure with name " << name
<< " previously registered --- request rejected" << endl;
#endif
}
return retVal;
}

bool deleteEntry(string name)
{
bool retVal = false;

map<string, T*>::iterator itor = _map.find(name);

if(itor != _map.end())
{
_map.erase(itor);
retVal = true;
}

if(retVal == false)
{
#ifdef DEBUG
cerr << "Datastructure with name " << name
<< " not found --- request rejected" << endl;
#endif
}
return retVal;
}

T* operator()(const string name)
{
T* retVal = NULL;

map<string, T*>::iterator itor = _map.find(name);

if(itor != _map.end())
{
retVal = itor->second;
}

if(retVal == NULL)
{
#ifdef DEBUG
cerr << "Cannot map datastructure with name " << name
<< " --- request rejected" << endl;
#endif
}

return retVal;
}

protected:
DSRegistry(){};
static DSRegistry* _instance;
map<string, T*> _map;
};

#endif //_DSREGISTRY_H_


//////////////////////////////////////////////////
#include <iostream>
#include "DSRegistry.h"

using namespace std;

DSRegistry<int>* DSRegistry<int>::_instance = NULL;

main()
{
int i1 = 1, i2 = 2, i3 = 3;

DSRegistry<int>::instance().addEntry("First" ,&i1);
DSRegistry<int>::instance().addEntry("Second" , &i2);
DSRegistry<int>::instance().addEntry("Third" , &i3);

int *val = DSRegistry<int>::instance()("Third");

if(val)
cout << "Returned value " << *val << endl;

}
 
V

Victor Bazarov

Generic said:
This is a two-part question.

Is it? Or is it simply a message with more than one question?

BTW, why did you cross-post to 'comp.sources.d'? I don't post there, I
don't know their rules, so, sorry, I am not cross-posting my reply.
(1) I have implemented a "Datastructure Registry" template class. I am
getting no compiler warnings with older compilers, but newer compilers
are generating the following error messages:
warning: implicit typename is deprecated,
please see the documentation for details

Can someone kindly suggest how to get rid of these warnings? [..]

Make sure to add 'typename' where your compiler suggests. Next time you
post about a compiler error message or a warning, indicate in the source
code _where_ the warning is emitted, _what_line_ it is related to.
(2) I want to use the "Datastructure Registry" template class to
implement a "Registry of Singletons", as mentioned in the GoF Design
patterns book. For this I want to do something like this:

typedefine the "Datastructure Registry" template-class as the "Registry
of Singletons" template-class.

I have tried various things, but nothing seems to be working.

typedef DSRegistry SingletonRegistry;
typedef DSRegistry<class T> SingletonRegistry<class T>;
typedef template DSRegistry<class T> template SingletonRegistry<class
T>;
typedef DSRegistry<class T> template SingletonRegistry<class T>;

None of those are going to work. There is not "template typedefs" in C++
(yet). To create a typedef (a synonym to a type), you need _a_type_, not
a _template_. In any case, the registry needs to be a singleton itself,
probably. And if it will work with all other singletons in a certain way,
shouldn't they all be of the same [base] class then?
Thanks,
Gus

[..]

V
 
M

Mr. Blackwell

Generic said:
This is a two-part question.

(1) I have implemented a "Datastructure Registry" template class. I am
getting no compiler warnings with older compilers, but newer compilers
are generating the following error messages:
warning: implicit typename is deprecated,
please see the documentation for details

add 'typename' in the line of the error message. For details see:
http://womble.decadentplace.org.uk/c++/template-faq.html
Can someone kindly suggest how to get rid of these warnings? The
source code follows.

(2) I want to use the "Datastructure Registry" template class to
implement a "Registry of Singletons", as mentioned in the GoF Design
patterns book. For this I want to do something like this:

typedefine the "Datastructure Registry" template-class as the "Registry
of Singletons" template-class.

I have tried various things, but nothing seems to be working.

typedef DSRegistry SingletonRegistry;

What is DSRegistry? If It's a template you cannot typedef it like that.
typedef DSRegistry<class T> SingletonRegistry<class T>;
typedef template DSRegistry<class T> template SingletonRegistry<class
T>;
typedef DSRegistry<class T> template SingletonRegistry<class T>;

You seem to be confused about templates and typedefs. They work
differently!
 
G

Generic Usenet Account

Mr. Blackwell said:
What is DSRegistry? If It's a template you cannot typedef it like that.


You seem to be confused about templates and typedefs. They work
differently!

Thanks for the clarification. After you mentioned about the
restriction on templates, I was able to get it working with
inheritance. Also, your suggestion of sticking in the "typename"
keyword worked.

///////////////////////////////////////////////
#ifndef _SINGLETONREGISTRY_H_
#define _SINGLETONREGISTRY_H_

#include "DSRegistry.h"

template <class T>
class SingletonRegistry : public DSRegistry<T>
{
};

#endif //_SINGLETONREGISTRY_H_


///////////////////////////////////////////////
#include <iostream>

#include "SingletonRegistry.h"

using namespace std;

DSRegistry<int>* DSRegistry<int>::_instance = NULL;

main()
{
int i1 = 1, i2 = 2, i3 = 3;

SingletonRegistry<int>::instance().addEntry("First" ,&i1);
SingletonRegistry<int>::instance().addEntry("Second" , &i2);
SingletonRegistry<int>::instance().addEntry("Third" , &i3);

int *val = SingletonRegistry<int>::instance()("Third");

if(val)
cout << "Returned value " << *val << endl;

}

-Gus
 

Ask a Question

Want to reply to this thread or ask your own question?

You'll need to choose a username for the site, which only take a couple of moments. After that, you can post your question and our members will help you out.

Ask a Question

Members online

No members online now.

Forum statistics

Threads
473,744
Messages
2,569,484
Members
44,903
Latest member
orderPeak8CBDGummies

Latest Threads

Top