Question

There is a declaration of template class with implicit parameters:

List.h

template <typename Item, const bool attribute = true>
class List: public OList <item, attribute>
{
    public:
    List() : OList<Item, attribute> () {}
    ....
};

I tried to use the fllowing forward declaration in a different header file:

Analysis.h

template <typename T, const bool attribute = true>
class List;

But G++ shows this error:

List.h:28: error: redefinition of default argument for `bool attribute'
Analysis.h:43: error:   original definition appeared here

If I use the forward declaration without implicit parameters

template <typename T, const bool attribute>
class List;

compiler does not accept this construction

Analysis.h

void function (List <Object> *list)
{
}

and shows the following error (i.e. does not accept the implicit value):

Analysis.h:55: error: wrong number of template arguments (1, should be 2)
Analysis.h:44: error: provided for `template<class T, bool destructable> struct List'
Analysis.h:55: error: ISO C++ forbids declaration of `list' with no type

Updated question:

I removed the default parameter from the template definition:

List.h

template <typename Item, const bool attribute>
class List: public OList <item, attribute>
{
    public:
    List() : OList<Item, attribute> () {}
    ....
};

The first file using class List has forward declaration with implicit value of the parameter attribute

Analysis1.h

template <typename T, const bool attribute = true>
class List;  //OK

class Analysis1
{
    void function(List <Object> *list); //OK
};

The second class using class List WITH forward definition using the implicit value

Analysis2.h

template <typename T, const bool attribute = true> // Redefinition of default argument for `bool attribute'
class List; 

class Analysis2
{
    void function(List <Object> *list); //OK
};

The second class using class List WITHOUT forward definition using the implicit value

Analysis2.h

template <typename T, const bool attribute> // OK
class List; 

class Analysis2
{
    void function(List <Object> *list); //Wrong number of template arguments (1, should be 2)
};

Answer 1

Simple. Remove the default value from the definition, since you already mentioned that in the forward declaration.

template <typename Item, const bool attribute = true> //<--- remove this 'true`
class List: public OList <item, attribute>
{
  //..
};

Write:

template <typename Item, const bool attribute>  //<--- this is correct!
class List: public OList <item, attribute>
{
  //..
};

Online Demo : http://www.ideone.com/oj0jK