annotation
@OnAttach
@OnAttach(Property) handler Name { … }
@OnAttach(Property) fires when the named property is structurally added to a live model instance with attach P on e — the property's fields are seeded first, then the hook runs in the context of that instance so it can read and adjust them. This is the structural birth of a property, the counterpart to @OnDetach; it differs from @OnEnable, which only un-pauses a property that already exists. Use it to react when a capability appears on an instance at runtime — a shield goes up, a status effect lands. The property name is a checked reference. Add @Public to also emit a prop_<Property>_attach event.
Example
program AttachHook {
property Tag { value: int = 0 }
property Shield { amount: int = 0 }
model Unit { Tag }
@OnAttach(Shield) handler RaiseShield { # fires when Shield is attached
print(Shield.amount + 10) # 15 — reads the seeded amount
}
handler Seed phase Start { spawn Unit { Tag { value: 1 } } }
handler AddShield phase Render {
for (unit) in query [Unit] {
attach Shield on self() { amount: 5 } # triggers @OnAttach
}
quit()
}
}