Object-oriented Software in Ada 95

Arrays 115
8.5.2 Attributes of multidimensional arrays
Like single dimensional arrays, various attributes can also be extracted from multidimensional arrays. For
multidimensional arrays it is, however, necessary to specify which dimension is to be interrogated. This is
achieved by appending the appropriate dimension to the attribute. For example, to find the number of elements in
the second dimension of the object Sqrs use The.Sqrs'Length(2). Section B.2, Appendix B lists attributes
that can be extracted from an object or type.
8.6 Initializing an array
A pixel on a true colour computer screen is represented by the three primary colours: red, blue, and green. Each
colour has an intensity ranging from 0 (dark) to 255 (bright). This is the RGB additive colour model used by
computer terminals and TVs, which is different from the CYMB subtractive colour model used in printing. In
Ada, a pixel could be represented by an array of three elements representing the intensities of the primary colours.
To represent the colour white, the intensity of each of the primary colours would be set to 255. A pixel can be
represented by the type Pixel_Array as follows:
type Colour is ( Red, Green, Blue );
type Intensity is range 0 .. 255;
type Pixel_Array is array( Colour ) of Intensity;
A single point on the screen could be represented by the object dot as follows:
Dot
: Pixel_Array;
which could be initialized to black or white with the following assignments:
Dot := ( 0, 0, 0 );
Dot := ( 255, 255, 255 );
--Black
--White
The values can be named by using the subscript to the array as follows:
Dot := ( Red=> 255, Green=>255, Blue=>255);
--White
An others clause can be used to let the remaining elements of the array take a particular value as in:
Dot := Pixel_Array'( Red=>255, others=>0 );
--Red
Note:
When the others clause is used, and at least one other element is given a value by a different means,
then the type of the constant must be specified. This is achieved by prefixing the constant with its type
name followed by a '.
Using a similar notation to that used in the case statement introduced in Section 3.8.1, a range of values may
also be specified:
Dot := ( Red=>255, Green=>255, Blue=>0 );
Dot := ( Red | Blue => 255, Green=>0 );
Dot := ( Red .. Blue => 127 );
--Yellow
--Purple
--Grey
© M A Smith - May not be reproduced without permission