Plugins

Introduction

The plugin system is the mechanism that allows Beetry to be extended with user-defined types.

Extension Dimensions

At a high level, a plugin consists of:

• a specification, which tells the framework how to interpret and interact with a given plugin type
• a factory, which allows runtime values to be recreated during deserialization

Plugins can extend the framework in two dimensions:

• behavior, by defining a separate plugin type for each node type
• data flow, by defining message types and the channels that transport them

Registration and Usage

All plugins are registered at compile time. Each plugin must declare a unique identifier. Registering two plugins of the same type with the same identifier results in a runtime error. See Caveats for current limitations.

To make plugins available, the module in which they are defined must be brought into scope.

Constraints

As already briefly mentioned in the Defining Tree chapter plugin-based extensibility constrains the structure.

This introduces the following constraints:

1. Inter-node communication that a node depends on has to be abstracted through an interface.
2. Any additional data needed when creating a node has to be expressed in a structured way.

The following sections present the concrete solutions to these constraints.