template specialization problem

This is a discussion on template specialization problem within the C++ Programming forums, part of the General Programming Boards category; Hello I would like to do: Code: std::list<some_templated_class> _list; _list.push_back(some_templated_class<some_object>(arguments)); but my compiler wont allow me to compile this. I ...

  1. #1
    l2u
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    template specialization problem

    Hello

    I would like to do:

    Code:
    std::list<some_templated_class> _list;
    _list.push_back(some_templated_class<some_object>(arguments));
    but my compiler wont allow me to compile this. I get error:
    unspecialized class template can't be used as a template argument for template parameter '_Ty', expected a real type

    Is there any other way to be able to do/override this?

    Thanks for help

  2. #2
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    Code:
    std::list<some_templated_class<some_object> > _list;
    You can't have the list hold templated objects of different types, since each is actually a different class, so you just need to specify the type for the some_templated_class.

  3. #3
    l2u
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    Quote Originally Posted by Daved View Post
    Code:
    std::list<some_templated_class<some_object> > _list;
    You can't have the list hold templated objects of different types, since each is actually a different class, so you just need to specify the type for the some_templated_class.
    I want to store handler within some_templated_class.
    For instance:

    some_templated_class<boost:bind(arguments)> _list;

    Each would be build with boost::bind but with different arguments.
    Is this possible to do?

    Maybe I could use boost::any or boost::tuple?

  4. #4
    Algorithm Dissector iMalc's Avatar
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    You'll need to store the pointers on the list instead, if the classes are not of identical type. Perhaps a boost ptr_container.
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  5. #5
    l2u
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    Quote Originally Posted by iMalc View Post
    You'll need to store the pointers on the list instead, if the classes are not of identical type. Perhaps a boost ptr_container.
    Is this the only solution?
    Does boost ptr_map exist?

  6. #6
    l2u
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    However, I get the same error with
    Code:
    boost::ptr_vector<some_templated_class> _list;
    Is there something I'm doing wrong?

  7. #7
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    I don't see how storing pointers will help, you still have to provide the type of the pointer.

    I don't actually know boost::bind well enough to figure out a good solution. boost::any and boost::variant can be used when you will have different types, so that is an option, but I don't know if it is a good option.

  8. #8
    l2u
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    Thanks for help Daved. Maybe someone else knows?

  9. #9
    Captain Crash brewbuck's Avatar
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    Quote Originally Posted by l2u View Post
    Thanks for help Daved. Maybe someone else knows?
    Store pointers to a base class and dispatch functionality through virtuals. In other words, derive the some_templated_class from a common NON-template base:

    Code:
    class my_base
    {
    public:
        virtual ~my_base(); // always need this
    
        virtual void do_this();
        virtual void do_that();
        // etc...
    };
    
    template <typename T>
    class some_templated_class : public my_base
    {
        // ...
    };
    Now, you store my_base pointers in the list, not instances:

    Code:
    std::list<my_base *> _list;
    _list.push_back(new some_templated_class<some_object>(arguments));
    You'll have to take care of cleaning up the dynamically allocated instances when the _list goes away. You can do that by using some kind of smart pointer.

  10. #10
    l2u
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    Cant I use boost ptr_container for this?

  11. #11
    Kiss the monkey. CodeMonkey's Avatar
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    Right. Then you wouldn't have to worry about the last thing brewbuck said.
    "If you tell the truth, you don't have to remember anything"
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  12. #12
    Algorithm Dissector iMalc's Avatar
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    Thanks brewbuck. That was what I was getting at.
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  13. #13
    Cat without Hat CornedBee's Avatar
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    In this case, however, boost::function (or tr1::function) may well be the type erasure root you seek, since what you want to store is bind expressions.
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  14. #14
    l2u
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    Quote Originally Posted by CornedBee View Post
    In this case, however, boost::function (or tr1::function) may well be the type erasure root you seek, since what you want to store is bind expressions.
    I took a look at boost function..
    Is it possible to call boost::function with unknown arguments?

    For instance:

    Code:
    boost::function<void(void)> func;
    func = boost::bind(&Test::func,&test, someargument, argument2);

  15. #15
    Cat without Hat CornedBee's Avatar
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    No, a compatible signature of the function must be given.
    All the buzzt!
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    "There is not now, nor has there ever been, nor will there ever be, any programming language in which it is the least bit difficult to write bad code."
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