Can anyone help with the following, I don't know if it's possible, but I'm
certain there must be a standard way of dealing with this.
I have the following:
template<typena me FooBar, typename Foo>
class Bar {
private:
Foo foo;
}
Now I want to be able to handle when 'Foo' is a primitive type, or more
specifically a primitive pointer type, like 'char *' and also when Foo is
itself a template class:
template<typena me FooBar, template<T> class Foo>
class Bar {
private:
Foo<FooBar> foo;
}
All the member functions and other fields of Bar are common to both
template classes. Can I do this with template specialization, if so how, I
don't quite get it.
I also tried to achieve this with the following, which isn't ideal,
because the client of the template must be aware that primitive types
must be wrapped in 'PrimitiveType' :
template<class T>
struct PrimitiveType
{
typedef T Type;
};
template<class T>
class WrappedClass
{
public:
typedef WrappedClass<T> Type;
private:
};
template<class FooBar, template<class T> class Foo>
class Bar {
public:
Foo<FooBar>::Ty pe wibble;
};
In theory, 'Bar' can have it's template parameter 'Foo' specified as
either 'PrimitiveType' or 'WrappedClass'.
Alas compilation with g++ simply gives me:
error: syntax error before `;' token
for the line Foo<FooBar>::Ty pe wibble;
I greatly appreciate any light shed on either of these issues.
Many thanks 3 2721
"case2005" <ca******@priva te.email.com> writes: Can anyone help with the following, I don't know if it's possible, but I'm certain there must be a standard way of dealing with this.
I have the following:
template<typena me FooBar, typename Foo> class Bar {
private: Foo foo; }
Now I want to be able to handle when 'Foo' is a primitive type, or more specifically a primitive pointer type, like 'char *' and also when Foo is itself a template class:
To find out if it is a pointer type you can do the following:
template< typename FooBar>
class Bar<FooBar, Foo*>
{
//......
};
If foo is some pointertype hte copiler will instanciate this
specialiization .
template<typena me FooBar, template<T> class Foo> class Bar {
private: Foo<FooBar> foo; }
All the member functions and other fields of Bar are common to both template classes. Can I do this with template specialization, if so how, I don't quite get it.
Maybe I got you wrong, but I think that's not necessary, because the
template will be instaciated with a concrete type, build by a template,
such as:
Bar<int, vector<double> >
for example. SO there is no such specialization necessary, IMHO.
I also tried to achieve this with the following, which isn't ideal, because the client of the template must be aware that primitive types must be wrapped in 'PrimitiveType' :
template<class T> struct PrimitiveType { typedef T Type; };
template<class T> class WrappedClass { public: typedef WrappedClass<T> Type;
private: };
template<class FooBar, template<class T> class Foo> class Bar { public:
Foo<FooBar>::Ty pe wibble; };
Here is
typename Foo<FooBar>::Ty pe wibble
required, becasue Type is a dependend name of the template Foo<...>.
I greatly appreciate any light shed on either of these issues.
I think what you are searchig for are so called typetraits: http://www.boost.org/libs/type_traits/index.html
This library work with a lot of differnet compilers.
If you use it you can ask the compiler if a special type is a primitive
type, or not and so on, and you'd have not to write a lot of template
specializations for each type.
HTH && Kind regards,
Nicolas
--
| Nicolas Pavlidis | Elvis Presly: |\ |__ |
| Student of SE & KM | "Into the goto" | \|__| |
| pa****@sbox.tug raz.at | ICQ #320057056 | |
|-------------------University of Technology, Graz----------------|
Nicolas
Thanks for this: typename Foo<FooBar>::Ty pe wibble
That worked. However, I don't understand:
To find out if it is a pointer type you can do the following:
template< typename FooBar> class Bar<FooBar, Foo*> { //...... };
What is Foo here? I get a parse error:
error: parse error before `>' token for:
class Bar<FooBar, Foo*>
Even if this does work, it's doen't give me the polymorphism I'm looking
for in the second template argument for a primitive pointer type template
argument or a templated class as the template argument.
Maybe I got you wrong, but I think that's not necessary, because the template will be instaciated with a concrete type, build by a template, such as:
Bar<int, vector<double> >
for example. SO there is no such specialization > necessary, IMHO.
No, 'Bar' accepts 'Foo' without T specified, notice that T is passed by
field 'foo' as 'FooBar'
So for example I might pass 'WrappedClass':
to
template<typena me FooBar, template<T> class Foo>
class Bar {
private:
Foo<FooBar> foo;
}
by
Bar<char, WrappedClass> bar;
bar.foo is then of type 'WrappedClass<c har>' yes?
I think what you've missed is that I want 'Bar' to
accept both a primitive pointer like 'char *' in it's second template
argument and also a templated class template argument. Do you follow?
Kind regards
case2005 wrote: Nicolas
Thanks for this:
typename Foo<FooBar>::Ty pe wibble
That worked. However, I don't understand:
To find out if it is a pointer type you can do the following:
template< typename FooBar> class Bar<FooBar, Foo*> { //...... };
What is Foo here? I get a parse error:
Sory, I should look like this:
template<typena me FooBar, typename Foo>
class Bar<FooBar, Foo*>
{
//.....
};
This should compile.
error: parse error before `>' token for:
class Bar<FooBar, Foo*>
Even if this does work, it's doen't give me the polymorphism I'm looking for in the second template argument for a primitive pointer type template argument or a templated class as the template argument.
So for example I might pass 'WrappedClass':
to
template<typena me FooBar, template<T> class Foo> class Bar {
private: Foo<FooBar> foo; }
by
Bar<char, WrappedClass> bar; bar.foo is then of type 'WrappedClass<c har>' yes?
Ok.
I think what you've missed is that I want 'Bar' to accept both a primitive pointer like 'char *' in it's second template argument and also a templated class template argument. Do you follow?
Yes. I'm not sure, but I think that this will not work, and you'd have
to pass the hole type such as PrimitiveTypeWr apper<SomeType> to the
template, I don;t really think that specializations to template template
arguments are working.
To solve yout Problem with the pointers to primitive types:
You can specializie to each type, such as int* double* and so on, or use
the type traits, to find out the charactaristics of the type, and
produce code accroding to the results.
HTH
Nicolas This thread has been closed and replies have been disabled. Please start a new discussion. Similar topics |
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