Quick start manual

9-12 Delphi Language Guide
Packages
The requires clause
The requires clause lists other, external packages that are used by the current
package. It functions like the uses clause in a unit file. An external package listed in
the requires clause is automatically linked at compile time into any application that
uses both the current package and one of the units contained in the external package.
If the unit files contained in a package make references to other packaged units, the
other packages should be included in the first package’s requires clause. If the other
packages are omitted from the requires clause, the compiler loads the referenced
units from their .dcu (Windows and Linux) or .dpu (Linux) files.
Avoiding circular package references
Packages cannot contain circular references in their requires clauses. This means that
• A package cannot reference itself in its own requires clause.
• A chain of references must terminate without rereferencing any package in the
chain. If package A requires package B, then package B cannot require package A;
if package A requires package B and package B requires package C, then package
C cannot require package A.
Duplicate package references
The compiler ignores duplicate references in a package’s requires clause. For
programming clarity and readability, however, duplicate references should be
removed.
The contains clause
The contains clause identifies the unit files to be bound into the package. Do not
include file-name extensions in the contains clause.
Avoiding redundant source code uses
A package cannot be listed in the contains clause of another package or the uses
clause of a unit.
All units included directly in a package’s contains clause, or indirectly in the uses
clauses of those units, are bound into the package at compile time. The units
contained (directly or indirectly) in a package cannot be contained in any other
packages referenced in requires clause of that package.
A unit cannot be contained (directly or indirectly) in more than one package used by
the same application.