Explain the principle of unidirectional data flow and its main features.

A unidirectional data flow is a concept where data in an application moves in a single direction, usually from top to bottom or from source to consumer. In iOS and other frontend frameworks, this helps simplify state management and avoid complex update cycles.

Main features:

• Data flows in one direction: changes occur in the data source, then update the view.
• Predictability: easier to track how and where data changes.
• Avoidance of side effects: no two-way bindings that can lead to unpredictable states.

Example: in Flux or Redux architecture, the state is stored centrally, and components receive data via props and do not modify it directly, but send actions that update the state.