Packages

• collection of resources
• encapsulated in one unit
• single library unit

Examples:

• TEXT_IO
• CALENDAR
• user-defined packages

Used for:

• collection of types and constants
• group of related subprograms
• user defined types and allowable operations

Benefits of packages:

• information hiding
• reuse
• abstract data types
• simpler programming

Package Organisation

• Package specification shows "what" it provides
• Package body defines "how" it is implemented.
• Both are separate from the user's program that uses the package.

Visibility

Compilation commands

Compilation order (separate compilations):

1. package specification
2. package body
3. program that uses package

Example

An example shows the organisation of a package of routines for working with rectangles, circles, etc, and a program that makes use of the package.

Developing packages

1. contents?
   • collection of types and constants
   • related subprograms
   • user defined type and operations
2. specification
   • interface for each operation
   • publicly-visible types, constants, (variables)
   • type implementations: private
   • file name:
     • sun ada: pack_s.a
     • gnat ada: pack.ads

3. body
   • subprogram code
   • extra declarations as needed
   • file name:
     • sun ada: pack_b.a
     • gnat ada: pack.adb