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

id	name	category	kind	tokens	sig	tip	order
fn-world_has	world_has	ecs	builtin	world_has	world_has(target, property) -> bool	Test whether a model instance currently carries a property.	50

world_has tests whether a model instance currently carries a given property, returning a boolean. It is the reflection-ABI equivalent of the membership test a query performs implicitly, and the safe guard to run before a world_get/world_set on a property an instance might not have. A property that has been disabled reads as absent here (its has-flag is clear), while one that is merely present with default values reads as present. Pass the target instance and the property id from world_prop_id.

Parameters:

• target — the model instance to test, an entity handle
• property — the property id, from world_prop_id

program CheckProperty {
  property Position { column: int = 0, row: int = 0 }
  property Shield   { amount: int = 0 }
  model Player { Position, Shield }

  handler Boot phase Start {
    spawn Hero { Position { column: 1, row: 1 }; Shield { amount: 2 } }
  }

  handler Inspect phase Update {
    let shield_property = world_prop_id("Shield")
    for (position) in query [Position, {Player}] {
      if world_has(self(), shield_property) { Screen.status("shielded") }
    }
  }
}