Chapter 12 Templates

1. Templates enable us to specify a range of related overloaded functions -- 
   called template functions -- or a range of related classes -- called template 
   classes.

2. To use function templates, the programmer writes a single function template 
   definition.  Based on the argument types provided in calls to this function, 
   C++ automatically generates separate functions to handle each type of call 
   appropriately. These are compiled along with the rest of the program's source 
   code.

3. All function template definition begin with the keyword template followed by 
   formal parameters to the function template enclosed in angle brackets (<>); 
   each formal parameter must be preceded by the keyword class (or the keyword 
   typename). Keyword class used to specify function template type parameters 
   means "any built-in type or user-defined type".

4. Template definition formal parameters are used to specify the types of the 
   arguments to the function, the return type of the function, and to declare 
   variables in the function.

5. The name of a formal parameter can be used only once in the parameter list of 
   a template header. Formal parameter names among template functions need not 
   be unique.

6. A function template itself may be overloaded in several ways.  We can provide 
   other function templates that specify the same function name but different 
   function parameters. A function template can also be overloaded by providing 
   other non-template functions with the same function name but different 
   function parameters.

7. Class templates provide the means for describing a class generically and 
   instantiating classes that are type-specific versions of this generic class.

8. Class templates are called parameterized types; they require type parameters 
   to specify how to customize a generic class template to form a specific 
   template class.

9. The programmer who wishes to use template classes writes one class template. 
   When the programmer needs a new type-specific class, the programmer uses a 
   concise notation and the compiler writes the source code for the template 
   class.

10. A class template definition looks like a conventional class definition 
    except that it is preceded by template < class T> to indicate this is a 
    class template definition with type parameter T indicating the type of the 
    class to be created. The type T is mentioned throughout the class header 
    and member function definitions as a generic type name.

11. The member function definitions outside the class template header each begin 
    with the header template <class T>. Then each function definition resembles 
    a conventional function except that the generic data on the class is always 
    listed generically as type parameter t. the binary scope resolution operator
    is used with the class template name to tie each member function definition 
    to the class template class template's scope as in Classname <T>.

12. It is possible to use non-type parameters in the header of a class template.

13. A calss for a specific type can be provided to override the class template 
    for that type.

14. A calss template can be derived from a template class. A class template can 
    be derived from a non-template class. A template class can be derived froma 
    class template. A non-class template class can be derived from a class 
    template.

15. Each template class instantiated from a class template has its own copy of 
    each static data member of the class template; all objects of that template 
    class share that one static data member. And as with static data members of 
    non-template classes, static data members of template classes must be 
    initialized at file scope.

16. Each template class gets a copy of the class template's static member 
    functions.

17. Template certainly offer the benefits of software reusability. But keep in 
    mind that multiple copies of template functions are still instantiated in 
    a program despite the fact that the template is written only once. These 
    copies can consume considerable memory.

18. Function templates, like macros, enable software reuse. But, unlike macros, 
    function templates help eliminate many type of errors because of the 
    scrutiny of full C++ type checking.