Struct Migrator 

pub struct Migrator<T: Versioned + DeserializeOwned> { /* private fields */ }

Schema migration pipeline for a Versioned type.

Add from → from + 1 steps with Migrator::step; the order in which they’re added does not matter — Migrator::run walks them in version order.

Migrator<T> is cheaply Clone (each step’s closure lives behind an Arc, so cloning is a handful of refcount bumps, not a deep copy) and Send + Sync whenever T is — which is what lets a Patch (crate::flush::Patch) closure retain its own copy of the migrator and re-run it against the document read fresh on the shared I/O worker thread, instead of the stale, possibly-out-of-date value this handle loaded at construction.

Implementations

impl<T: Versioned + DeserializeOwned> Migrator<T>

pub fn new() -> Self

Create an empty migrator with no steps registered.

If T::CURRENT_VERSION is 1 (the initial schema) or the file is already at the current version, no steps are needed and run will succeed immediately.

pub fn step<F>(self, from: u32, func: F) -> Self

where F: Fn(Value) -> Result<Value, String> + Send + Sync + 'static,

Register a step that promotes a value from from to from + 1. Steps may be registered in any order; run finds the right one for the current version on demand.

pub fn run(&self, raw: Value) -> Result<T, MigrationError>

Migrate raw from its on-disk version up to T::CURRENT_VERSION, then deserialize.

Reads the version directly from the version field of the raw toml::Value — never deserializes-then-checks, because a v1 payload typically fails to deserialize as the v2 type.

Files missing the version field are treated as v1 (legacy).

Trait Implementations

impl<T: Versioned + DeserializeOwned> Clone for Migrator<T>

fn clone(&self) -> Self

Hand-written rather than #[derive(Clone)]: a derive would add a spurious T: Clone bound (from the PhantomData<T> field) even though nothing here actually needs it — Vec<Step> clones just fine on its own (each Step::func is an Arc, so this is a handful of refcount bumps).

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl<T: Versioned + DeserializeOwned> Debug for Migrator<T>

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl<T: Versioned + DeserializeOwned> Default for Migrator<T>

fn default() -> Self

Returns the “default value” for a type.