Strategy — Readonly and Immutability

When to use

• The task models a value or domain concept — money, a date range, coordinates — as an object whose identity is defined by its contents.
• The task is to fix or refactor a mutable object whose in-place changes are causing hard-to-trace bugs across callers.
• The state will be passed around and shared among multiple callers or components that should not surprise one another with mutations.

When NOT to use