'Pure functional' tasks

To maximise their reusability, developers are advised to write Tasks in a way which either:

• Changes the application's state
• Gets information from the application without changing its state

This draws from the lessons that writing pure functions teaches us. If 'getting some information' has unwanted or unexpected side-effects then the task becomes less reusable. If a task must have side effects then consider separating the parts of it which do not require those side-effects into a lower-level task which is reusable without the side-effects. That lower-level task would then be consumed by a higher-level task which does include the side-effects.