Modules and packages

Programs sources can be organized in packages of modules.

The structure of a program consists of a main module (defining the MAIN block), and several modules, that can be grouped in a hierarchy of packages.

A package is a collection of modules, located in directories that define a package hierarchy.

For backward compatibility, Genero BDL allows flat module organization, with a program linking process. However, new developments should use imported modules and packages, to define the module dependencies as in other modern programming languages. The import solution does not require a linking phase, and allows better error checking at compile time.

Packages of modules must be organized in a tree of directories. The modules are named by the filename of the .4gl source, while packages are named by their directory name.

Tip:

Use lower case names for modules and packages to avoid any cross-platform issues regarding file system case sensitivity.

A project source tree start at the top-dir directory:

top-dir
|-- prog1.4gl
|-- package_1
|   |-- module_11.4gl
|   |-- module_12.4gl
|   |-- module_13.4gl
|-- package_2
|   |-- module_21.4gl
|   |-- module_22.4gl
|   |-- sub_package_22
|   |   |-- module_221.4gl
|   |   |-- module_222.4gl
...

Each module must define the package it belongs to, by reflecting its directory path starting from top-dir. In the above directory structure, the module_221.4gl must start with the following PACKAGE instruction:

PACKAGE package_2.sub_package_22
...

Modules using program elements of a set of modules grouped in a package can import the whole package with IMPORT FGL package-path.*. For example, the prog1.4gl main module can use these instructions:

IMPORT FGL package_1.*
IMPORT FGL package_2.sub_package_22.*
...

However, best practice is to list the required modules, because packages can be extended with more modules:

IMPORT FGL package_1.module_11
IMPORT FGL package_1.module_13
IMPORT FGL package_2.sub_package_22.module_221
...