Pony code is organised into packages. Each program and library is a single package, possibly using other packages.
The package structure
The package is the basic unit of code in Pony. It corresponds directly to a directory in the file system, all Pony source files within that directory are within that package. Note that this does not include files in any sub-directories.
Every source file is within exactly one package. Hence all Pony code is in packages.
A package is usually split into several source files, although it does not have to be. This is purely a convenience to allow better code organisation and the compiler treats all the code within a package as if it were from a single file.
The package is the privacy boundary for types and methods. That is:
- Private types (those whose name starts with an underscore) can be used only within the package in which they are defined.
- Private methods (those whose name starts with an underscore) can be called only from code within the package in which they are defined.
It follows that all code within a package is assumed to know and trust, all the rest of the code in the package.
There is no such concept as a sub-package in Pony. For example, the packages “foo/bar” and “foo/bar/wombat” will, presumably, perform related tasks but they are two independent packages. Package “foo/bar” does not contain package “foo/bar/wombat” and neither has access to the private elements of the other.