Hello all,
Please see my question embedded in comment form below.
Thanks,
Dave
#include <iostream>
#include <boost/shared_ptr.hpp>
using namespace std;
using namespace boost;
// A base class
class Deleter
{
public:
Deleter() {}
virtual ~Deleter() {}
};
// A derived class
class MyClass: public Deleter
{
public:
MyClass(int data): m_data(data) {}
virtual ~MyClass() {}
void DoIt() const
{
cout << m_data << endl;
}
private:
int m_data;
};
// A factory for objects that are constructed with 0 or 1 parameters.
template <class T>
class Factory
{
public:
static shared_ptr<T> Create()
{
cout << "Primary Factory invoked" << endl;
return shared_ptr<T>(new T());
}
template <class P1>
static shared_ptr<T> Create(P1 p1)
{
cout << "Primary Factory invoked" << endl;
return shared_ptr<T>(new T(p1));
}
};
// Here's where I don't have things right. I'd like to specialize Factory
for types derived from Deleter.
// How may I do so?
template <class T> // ?????????????
class Factory<Deleter> // ?????????????
{
static shared_ptr<T> Create()
{
cout << "Specialized Factory invoked" << endl;
return shared_ptr<T>(new T());
}
template <class P1>
static shared_ptr<T> Create(P1 p1)
{
cout << "Specialized Factory invoked" << endl;
return shared_ptr<T>(new T(p1));
}
};
int main()
{
shared_ptr<MyClass> ptr(Factory<MyClass>::Create(42));
ptr->DoIt();
}
6  1581 
* Dave:
#include <iostream>
#include <boost/shared_ptr.hpp>
using namespace std;
using namespace boost;
// A base class
class Deleter
{
public:
Deleter() {}
virtual ~Deleter() {}
};
What's the purpose of Deleter?
// A derived class
class MyClass: public Deleter
{
public:
MyClass(int data): m_data(data) {}
virtual ~MyClass() {}
void DoIt() const
{
cout << m_data << endl;
}
private:
int m_data;
};
// A factory for objects that are constructed with 0 or 1 parameters.
template <class T>
class Factory
{
public:
static shared_ptr<T> Create()
{
cout << "Primary Factory invoked" << endl;
return shared_ptr<T>(new T());
}
template <class P1>
static shared_ptr<T> Create(P1 p1)
{
cout << "Primary Factory invoked" << endl;
return shared_ptr<T>(new T(p1));
}
};
And what's your purpose in using a factory?
Depending on your purpose there may be a better alternative.
// Here's where I don't have things right. I'd like to specialize Factory
for types derived from Deleter.
// How may I do so?
What's the purpose of that?
Anyway if you really must you have at least three options: add a
template parameter that you can use for partial specialization, or use a
derived class, or let the general implementation defer to a specific
implementation if one exists.
--
A: Because it messes up the order in which people normally read text.
Q: Why is it such a bad thing?
A: Top-posting.
Q: What is the most annoying thing on usenet and in e-mail?
Dave wrote: Hello all,
Please see my question embedded in comment form below.
Thanks,
Dave
#include <iostream>
#include <boost/shared_ptr.hpp>
using namespace std;
using namespace boost;
// A base class
class Deleter
{
public:
Deleter() {}
virtual ~Deleter() {}
};
// A derived class
class MyClass: public Deleter
{
public:
MyClass(int data): m_data(data) {}
virtual ~MyClass() {}
void DoIt() const
{
cout << m_data << endl;
}
private:
int m_data;
};
// A factory for objects that are constructed with 0 or 1 parameters.
template <class T>
class Factory
{
public:
static shared_ptr<T> Create()
{
cout << "Primary Factory invoked" << endl;
return shared_ptr<T>(new T());
}
template <class P1>
static shared_ptr<T> Create(P1 p1)
{
cout << "Primary Factory invoked" << endl;
return shared_ptr<T>(new T(p1));
}
};
// Here's where I don't have things right. I'd like to specialize Factory
for types derived from Deleter.
// How may I do so?
template <class T> // ?????????????
class Factory<Deleter> // ?????????????
{
static shared_ptr<T> Create()
{
cout << "Specialized Factory invoked" << endl;
return shared_ptr<T>(new T());
}
template <class P1>
static shared_ptr<T> Create(P1 p1)
{
cout << "Specialized Factory invoked" << endl;
return shared_ptr<T>(new T(p1));
}
};
int main()
{
shared_ptr<MyClass> ptr(Factory<MyClass>::Create(42));
ptr->DoIt();
}
To get the effect you want, put a compile-time check for inheritance
from Deleter in your Create() functions. Using Boost Typetraits and
static asserts, it would look something like:
static shared_ptr<T> Create()
{
BOOST_ASSERT( (is_base_of<Deleter, T>::value) );
// ...
}
Note the extra set of parentheses to overcome the preprocessor's
ignorance of templates. Using this code, you'd get a compile-time error
if T is not derived from Deleter.
Cheers! --M
"mlimber" <ml*****@gmail.com> wrote in message
news:11**********************@o13g2000cwo.googlegr oups.com... Dave wrote: Hello all,
Please see my question embedded in comment form below.
Thanks,
Dave
#include <iostream>
#include <boost/shared_ptr.hpp>
using namespace std;
using namespace boost;
// A base class
class Deleter
{
public:
Deleter() {}
virtual ~Deleter() {}
};
// A derived class
class MyClass: public Deleter
{
public:
MyClass(int data): m_data(data) {}
virtual ~MyClass() {}
void DoIt() const
{
cout << m_data << endl;
}
private:
int m_data;
};
// A factory for objects that are constructed with 0 or 1 parameters.
template <class T>
class Factory
{
public:
static shared_ptr<T> Create()
{
cout << "Primary Factory invoked" << endl;
return shared_ptr<T>(new T());
}
template <class P1>
static shared_ptr<T> Create(P1 p1)
{
cout << "Primary Factory invoked" << endl;
return shared_ptr<T>(new T(p1));
}
};
// Here's where I don't have things right. I'd like to specialize
Factory for types derived from Deleter.
// How may I do so?
template <class T> // ?????????????
class Factory<Deleter> // ?????????????
{
static shared_ptr<T> Create()
{
cout << "Specialized Factory invoked" << endl;
return shared_ptr<T>(new T());
}
template <class P1>
static shared_ptr<T> Create(P1 p1)
{
cout << "Specialized Factory invoked" << endl;
return shared_ptr<T>(new T(p1));
}
};
int main()
{
shared_ptr<MyClass> ptr(Factory<MyClass>::Create(42));
ptr->DoIt();
}
To get the effect you want, put a compile-time check for inheritance
from Deleter in your Create() functions. Using Boost Typetraits and
static asserts, it would look something like:
static shared_ptr<T> Create()
{
BOOST_ASSERT( (is_base_of<Deleter, T>::value) );
// ...
}
Note the extra set of parentheses to overcome the preprocessor's
ignorance of templates. Using this code, you'd get a compile-time error
if T is not derived from Deleter.
But I don't want a compile-time error if T is not derived from Deleter. In
that case, I would just want the primary Factory template to be used rather
than the specialization.
Cheers! --M
Dave wrote: "mlimber" <ml*****@gmail.com> wrote in message
news:11**********************@o13g2000cwo.googlegr oups.com... Dave wrote: Hello all,
Please see my question embedded in comment form below.
Thanks,
Dave
#include <iostream>
#include <boost/shared_ptr.hpp>
using namespace std;
using namespace boost;
// A base class
class Deleter
{
public:
Deleter() {}
virtual ~Deleter() {}
};
// A derived class
class MyClass: public Deleter
{
public:
MyClass(int data): m_data(data) {}
virtual ~MyClass() {}
void DoIt() const
{
cout << m_data << endl;
}
private:
int m_data;
};
// A factory for objects that are constructed with 0 or 1 parameters.
template <class T>
class Factory
{
public:
static shared_ptr<T> Create()
{
cout << "Primary Factory invoked" << endl;
return shared_ptr<T>(new T());
}
template <class P1>
static shared_ptr<T> Create(P1 p1)
{
cout << "Primary Factory invoked" << endl;
return shared_ptr<T>(new T(p1));
}
};
// Here's where I don't have things right. I'd like to specialize Factory for types derived from Deleter.
// How may I do so?
template <class T> // ?????????????
class Factory<Deleter> // ?????????????
{
static shared_ptr<T> Create()
{
cout << "Specialized Factory invoked" << endl;
return shared_ptr<T>(new T());
}
template <class P1>
static shared_ptr<T> Create(P1 p1)
{
cout << "Specialized Factory invoked" << endl;
return shared_ptr<T>(new T(p1));
}
};
int main()
{
shared_ptr<MyClass> ptr(Factory<MyClass>::Create(42));
ptr->DoIt();
}
To get the effect you want, put a compile-time check for inheritance
from Deleter in your Create() functions. Using Boost Typetraits and
static asserts, it would look something like:
static shared_ptr<T> Create()
{
BOOST_ASSERT( (is_base_of<Deleter, T>::value) );
// ...
}
Note the extra set of parentheses to overcome the preprocessor's
ignorance of templates. Using this code, you'd get a compile-time error
if T is not derived from Deleter.
But I don't want a compile-time error if T is not derived from Deleter. In
that case, I would just want the primary Factory template to be used rather
than the specialization.
Sorry. I didn't read it closely enough. Just use the compile-time
constant is_base_of<Deleter, T>::value to select an implementation.
Something like:
template<class T>
struct DefaultFactory
{
static shared_ptr<T> Create() { /*...*/ }
// ...
};
template<class T>
struct SpecialFactory
{
static shared_ptr<T> Create() { /*...*/ }
// ...
};
template<bool IsSpecial, class T> struct FactorySelector;
template<class T>
struct FactorySelector<true,T>
{
typedef SpecialFactory<T> Factory;
};
template<class T>
struct FactorySelector<false,T>
{
typedef DefaultFactory<T> Factory;
};
template<class T>
struct Factory
: public FactorySelector<
is_base_of<Deleter, T>::value, T >::Factory
{};
Cheers! --M
"mlimber" <ml*****@gmail.com> wrote in message
news:11**********************@g47g2000cwa.googlegr oups.com... Dave wrote: "mlimber" <ml*****@gmail.com> wrote in message
news:11**********************@o13g2000cwo.googlegr oups.com... Dave wrote:
> Hello all,
>
> Please see my question embedded in comment form below.
>
> Thanks,
> Dave
>
> #include <iostream>
> #include <boost/shared_ptr.hpp>
>
> using namespace std;
> using namespace boost;
>
> // A base class
> class Deleter
> {
> public:
> Deleter() {}
> virtual ~Deleter() {}
> };
>
> // A derived class
> class MyClass: public Deleter
> {
> public:
> MyClass(int data): m_data(data) {}
> virtual ~MyClass() {}
>
> void DoIt() const
> {
> cout << m_data << endl;
> }
>
> private:
> int m_data;
> };
>
> // A factory for objects that are constructed with 0 or 1
parameters. > template <class T>
> class Factory
> {
> public:
> static shared_ptr<T> Create()
> {
> cout << "Primary Factory invoked" << endl;
> return shared_ptr<T>(new T());
> }
>
> template <class P1>
> static shared_ptr<T> Create(P1 p1)
> {
> cout << "Primary Factory invoked" << endl;
> return shared_ptr<T>(new T(p1));
> }
> };
>
> // Here's where I don't have things right. I'd like to specialize
Factory > for types derived from Deleter.
> // How may I do so?
> template <class T> // ?????????????
> class Factory<Deleter> // ?????????????
> {
> static shared_ptr<T> Create()
> {
> cout << "Specialized Factory invoked" << endl;
> return shared_ptr<T>(new T());
> }
>
> template <class P1>
> static shared_ptr<T> Create(P1 p1)
> {
> cout << "Specialized Factory invoked" << endl;
> return shared_ptr<T>(new T(p1));
> }
> };
>
> int main()
> {
> shared_ptr<MyClass> ptr(Factory<MyClass>::Create(42));
>
> ptr->DoIt();
> }
To get the effect you want, put a compile-time check for inheritance
from Deleter in your Create() functions. Using Boost Typetraits and
static asserts, it would look something like:
static shared_ptr<T> Create()
{
BOOST_ASSERT( (is_base_of<Deleter, T>::value) );
// ...
}
Note the extra set of parentheses to overcome the preprocessor's
ignorance of templates. Using this code, you'd get a compile-time
error if T is not derived from Deleter.
But I don't want a compile-time error if T is not derived from Deleter.
In that case, I would just want the primary Factory template to be used
rather than the specialization.
Sorry. I didn't read it closely enough. Just use the compile-time
constant is_base_of<Deleter, T>::value to select an implementation.
Something like:
template<class T>
struct DefaultFactory
{
static shared_ptr<T> Create() { /*...*/ }
// ...
};
template<class T>
struct SpecialFactory
{
static shared_ptr<T> Create() { /*...*/ }
// ...
};
template<bool IsSpecial, class T> struct FactorySelector;
template<class T>
struct FactorySelector<true,T>
{
typedef SpecialFactory<T> Factory;
};
template<class T>
struct FactorySelector<false,T>
{
typedef DefaultFactory<T> Factory;
};
template<class T>
struct Factory
: public FactorySelector<
is_base_of<Deleter, T>::value, T >::Factory
{};
Cheers! --M
Hopefully the last question...
Has is_base_of<> been replaced? I cannot find it for the life of me...
Dave wrote:
[snip] Hopefully the last question...
Has is_base_of<> been replaced? I cannot find it for the life of me...
It's in the Boost.Typetraits documentation: http://boost.org/doc/html/boost_type...its.is_base_of
but it looks like it has been renamed is_base_and_derived. Sorry about
the confusion.
Cheers! --M This thread has been closed and replies have been disabled. Please start a new discussion. Similar topics
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