ludic/docs/language/ecs/fn-world_set.md

id	name	category	kind	tokens	sig	tip	order
fn-world_set	world_set	ecs	builtin	world_set	world_set(target, property, field, value)	Write one field of a model instance by numeric id (reflection ABI).	50

world_set writes a single field of a model instance by numeric id — the id-based counterpart to an ordinary position.column = … assignment, used when the property is not known at compile time. You give the target instance, the property id (from world_prop_id), the field id (from world_field_id), and the new value; the value is stored just as a direct assignment would. It returns nothing. Together with world_get, world_has, and the resolver functions, it lets a mod or tool mutate any field on any instance generically, which is how the reflection ABI mirrors the compiled query/field access at runtime.

Parameters:

• target — the model instance to write to, an entity handle
• property — the property id, from world_prop_id
• field — the field id within that property, from world_field_id
• value — the new integer value to store

program WriteField {
  property Position { column: int = 0, row: int = 0 }
  model Player { Position }

  handler Boot phase Start {
    spawn Hero { Position { column: 0, row: 0 } }
  }

  handler Nudge phase Update {
    let position_property = world_prop_id("Position")
    let column_field = world_field_id(position_property, "column")
    for (position) in query [Position, {Player}] {
      world_set(self(), position_property, column_field, position.column + 1)
    }
  }
}