Typestate pattern in Rust

The Typestate Pattern in Rust

Typestate used to be a language feature in Rust before 1.0, but it was removed due to its significant complexity added to the language and type system ¹

Type state allowed encoding state machines into the type system, enabling the compiler to catch certain classes of errors at compile-time

• Define uninitializable type for each state of your object

pub enum Ready {} // No variants, cannot be initialized

• Make your type generic over its state using (see PhantomData)
• Implement methods only for relevant states
• Methods that update state take owned self and return instance with new state

When to use

• if you problem is like a state machine
• Ensure at compile-time that no invalid operation is done

Related

• newtype idiom

Footnotes

1. Typestates in Rust ↩