Command-class: Virtual Command Class

In tengfei/commandr: Command pattern in R

Description

Command represents any generic operation and is often combined with other such objects in a sequence. This is the foundation for implementations of pipelines, logging, undo stacks, etc, according to the Command design pattern. Since Command is virtual, it cannot be constructed directly. Rather, one should construct an instance of a concrete derivative, like Operation or Protocol.

Details

Developers are encouraged to extend Command for new implementations of the Command design pattern.

There are a number of generics for which a Command derivative should provide methods:

displayName(object): Gets the display name of the command, i.e., the name displayed in a user interface. The default implementation returns the class name. A Command may provide other visual attributes; the display name is considered fundamental for integration with user interfaces.

widget(object, ...): Creates a widget for viewing and controlling this object. No default implementation.

rev(object): Returns a Command that performs the opposite action, i.e., to undo an operation. This will not always be possible, so it is acceptable for a subclass to leave this unimplemented.

active(object): Gets whether the command is considered active. This is meant for temporarily disabling or enabling a command without removing it completely from, e.g., a pipeline or GUI menu. No default implementation.

Of course, a Command implementation also needs a method that executes the command. The signature for such a function highly depends on the nature of the command, so the generic depends on the class.

Author(s)

Michael Lawrence

tengfei/commandr documentation built on May 31, 2019, 8:33 a.m.