Lecture 9 – September 24th

We discussed problems people were having with the Fractions program that was due today

We talked about Ada’s ability to overload existing operators such as  +, -, *, /, <

To overload an existing operator (+, - ,*,/) you have to  put them in “ “ and define the function. We can see how this is done in both  Fractions.ads and Fractions.adb.

We talked about how to call one of these overloaded functions: 

myFraction := Fractions.”+”(parameters)

 

We went over and answered the questions that were associated with Fractions.ads and Fractions.adb and were found in Fraction.doc  (Blackboard Assignment4)

Remember:  Function calls always appear on the right side of an assignment operator .

On the left side of the operator is a variable holding the type of value returned by the function.

 

Every Ada procedure must have at least one executable statement in it.

 To test  the syntax of your declarations before you do any real work,  use a NULL;  statement.

 

< >  with no space between them in Ada is called a “box”

In our generic package Discrete_Set  the “+” is an overloaded operator

Three operations come for free with private types:

Test elements of a private type for being equal

You can test element of a private type for being not equal

You can assign an element of a private type to another element of a private type

 

We discussed how the private type set_type is represented in the Discrete_Set package.  It is an array of Booleans with as many elements as there are elements in the set_type. 

 

For example, define the enumerated type Fruit defined as shown below.

TYPE Fruit is (apple, berry cherry); 

 

Supposed also that you had instantiatiated the package Discrete_Set as follows:

PACKAGE mySet IS NEW Discrete_Set (Element_Type => Fruit);

 

Further suppose that you declared setA as follows. 

setA : mySet.Set_type.

 

Further suppose that you initialized it to the package defined constant Universal_Set as follows.

setA := mySet.Universal_Set;

 

The diagram below shows what would be in  setA  which  is a three-element array of Booleans whose elements can only be accessed through the functions in the Discrete_Set package.

 

            apple                                        berry                                                     cherry

true

true

true

 

If you had initialized setA to mySet.EmptySet, then all of the values would be false.