Multiple Inheritance

1
Multiple Inheritance

• Sometimes it is useful for derived classes to
  inherit from two base classes.
• This feature not available in Smalltalk or Java.

2
Potential Problems with Multiple Inheritance.

• Inheriting the same member name from different
  base classes.
• Inheriting members of a base class through more
  than one inheritance path.

3
The problem

• Many functions have the same behaviour but
  operate on different types.
• Hence, basically the same function must be
  rewritten several times to accommodate the
  different types.

4
Templates

• C permits the use of templates.
• Same code used with various types.
• Enables parametric polymorphism

5
Types of template

• Two types
• class template
• function template

6
Function Templates

• Function definition preceded by
• template ltclass TYPEgt
• where TYPE is an arbitrary type.

7
Example

• template ltclass TYPEgt
• void swap (TYPE x, TYPE y)

8
Example

• int j double k
• swap (j, k)
• causes a compile-time error.
• This is called a unification error.

9
Example

• templateltclass T1, class T2gt
• void copy(T1 a, T2 b, int n)
• for (int i 0 i lt n i)
• ai bi

10
Special cases

• template ltclass Tgt
• void swap (T x, T y)
• T temp
• temp x x y y temp

11
Example

• int i, j
• char str1100, char str2100, ch
• swap (i, j)
• swap (str150, str233)
• swap (i, ch)
• swap (str1, str2)

12
Example

• void swap (char s1, char s2)
• appropriate code

13
Overloaded function-selection algorithm.

• 1. Exact match with trivial conversions on
  nontemplate functions.
• 2. Exact match using function templates.
• 3. Ordinary argument resolution on nontemplate
  functions.

14
Class templates

• Allows an arbitrary type to be used in a class
  definition.
• Saves us from rewriting class declarations where
  the only variation is the type declarations.

15
Class templates

• The class declaration prefaced by
• template ltclass identifiergt
• identifier represents some arbitrary type which
  can be used throughout the declaration of the
  class

16
Defining classes

• When defining a class that uses a class template,
  the angle brackets indicating the type must be
  included.

17
Member functions

• Member functions defined within a class are
  inline.
• If defined externally the full angle bracket
  declaration must be used.

18
Example

• TYPE top_of() const return stop
• would be rewritten as
• template ltclass TYPEgt TYPE stackltTYPEgttop_o
  f() const
• return stop

19
friends

• Template functions can contain friends.
• A friend function that does not use a template
  specification is a friend to all instantiations.
• A friend function that incorporates template
  arguments is specifically a friend of its
  instantiated class.

20
Static members

• Static members are not universal but specific to
  each instantiation.

21
Example

• Template class ltTgt
• class foo
• public static int count
• foo ltintgt a
• foo ltdoublegt b

22
Example

• The static variables
• fooltintgtcount
• fooltdoublegtcount
• are distinct.