Inline Actor Migration

Migrate actor state across canister upgrades using a migration expression attached to the actor. Each upgrade has at most one migration function.

For multi-migration with a migrations/ directory, load migrating-motoko-enhanced instead.

When to Use

Implicit migration (no code needed)

The runtime allows the upgrade if the new program is compatible with the old:

• Adding actor fields
• Removing actor fields
• Changing mutability (var ↔ let)
• Adding variant constructors
• Widening types (Nat → Int)

Explicit migration required