Lecture 10 – September 26, 2007

We looked at functions in the body of package Fractions and worked in teams to determine if they were correct or not.

We traced several of them on the board.

We discussed that when we call an overloaded function we need to use a somewhat cumbersome call such as

myFraction := Fractions.”+” ( fractionA, fractionB);

This is a form of prefix notation.

If we use a USE clause for the package we can use infix notation to call the function as

myFraction := fractionA + fractionB;

It is important to know how to use the fully qualified notation because there are times when a USE clause is not sufficient (i.e. the compiler can not tell which function from which package you want). This can happen if the same operator is overloaded in a number of packages and the operands in the function are of the same time.

We looked at a snippet of code from Professor Adams’ test program and discussed the fact that whatever occurs between the word GENERIC and the word PACKAGE in a generic package specification is a package parameter that must be used in the package instantiation.

ÏÏÏWITH Discrete_Set;
ÏÏÏWITH Ada.text_io;

ÏÞßàPROCEDURE set_test IS
ÏÏ§ÏïÏTYPE fruit IS (apple, berry, cherry, plum, peach, apricot, mango); -- enumerated type declaration
ÏÏ§ÏØÓìPACKAGE fruit_io IS NEW ada.text_io.enumeration_io (fruit);       -- instantiation for printing/reading values of the enumerated type
ÏÏ§ÏØÓìPACKAGE mySet IS NEW Discrete_Set(Element_Type => fruit);         -- instantiation of generic package Discrete_Set
ÏÏ§
ÏÏ§ÏíÏsetA, setB, setC : mySet.Set_Type;                  -- declarations of variables of Set_Type (called set variables in assignment)
ÏÏ§ÏíÏisInSet : boolean;
ÏÏ§
ÏÏ§begin
ÏÏ§
ÏÏ¨¹¹ÏsetA := mySet.Universal_Set;                                         -- initializing setA to Universal_Set
ÏÏ¨¹¹ÏsetB := mySet.Empty_Set;                                             -- initializing setB to the Empty_Set
ÏÏ¨¹¹ÏsetC := mySet."+"(setA, setB);                                      -- initializing setC to the union of setA and setB
ÏÏ§
ÏÏ§   -- listing all of the elements that are in setA,one per line
ÏÏ¨¹¹±FOR i IN fruit LOOP
ÏÏ§ÏÏ7¹³´IF (mySet.is_Member (setA, i)) THEN       -- yes, I cheated and embedded a function call in an IF statement
ÏÏ§ÏÏ5Ï6¨¹¹Ïfruit_io.put (i);
ÏÏ§ÏÏ5Ï6¾¹¹ÏAda.text_io.new_line;
ÏÏ§ÏÏ5Ï¶ÏEND IF;
ÏÏ§ÏÏ°END LOOP;
ÏÏ¨¹¹ÏAda.text_io.new_line;
End set_test;

Note the following:

Your enumerated type does not have to be fruit.

Your program will be longer than mine which just shows you declarations and two function calls.