Object-oriented Software in Ada 95

176 Child libraries
The function Image returns a string representing a rational number in canonical form. The strategy used is to
use the inbuilt function Integer’Image to convert a number into a character string. However, as this leaves a
leading space for the sign character an internal function Trim is provided to strip off the leading character from
such a string.
The nested function To_String delivers a string representation in canonical form of a positive rational
number. By using a single case of recursion this function can deal with the case when a rational number is of the
form “a b/c”.
function Image( The:in Rational ) return String is
Above : Integer := The.Above;
Below : Integer := The.Below;
function Trim( Str:in String ) return String is
begin
return Str( Str'First+1 .. Str'Last );
end Trim;
function To_String( Above, Below : in Integer )
return String is
begin
if Above = 0 then --No fraction
return "";
elsif Above >= Below then --Whole number
return Trim( Integer'Image(Above/Below) ) & " " &
To_String( Above rem below, Below );
else
return Trim( Integer'Image( Above ) ) & "/" &
Trim( Integer'Image( Below ) );
end if;
end To_String;
begin
if Above = 0 then
return "0";
--Zero
elsif Above < 0 then
return "-" & To_String( abs Above, Below ); ---ve
else
return To_String( Above, Below );
end if;
end Image;
end Class_Rational;
12.3 A bounded string class
--+ve
A partial solution to overcome the fixed size limitations of Ad strings is to use a discriminated record that can
hold a string of any length up to a pre-defined maximum. The responsibilities of the class Bounded_String
which holds a variable length string is as follows:
Method
Operator:
&
Operators:
> >= <