ECS:entities_with

Returns all entities that have a Component of a specific class or inheriting from it.

The same data can obtained by creating a Query matching on a single component class. Both techniques have about the same performance (O(n) where n is number of entities returned). Using a query requires a bit more ceremony but also gives you a way to tell when entities receive/lose the required component. Using this method has the benefit of returning immediately up to date results, while queries are only updated during ECS:update.

Usage

ecs:entities_with(class)

Arguments

Name	Type	Description
class	string or component class	The component class that must be present on entities for them to be returned.

Returns

Name	Type	Description
entities	table	A table where every key is an Entity.

Examples

local Health = Class("Health", crystal.Component);
local ecs = crystal.ECS:new();
local warrior = ecs:spawn(crystal.Entity);
local fairy = ecs:spawn(crystal.Entity);
local save_point = ecs:spawn(crystal.Entity);
warrior:add_component("Health");
fairy:add_component("Health");

-- Loop over warrior and fairy, but not save_point
for entity in pairs(ecs:entities_with("Health")) do
  -- Do something with entities that have a health component
end