Functions to setup and control systems.

A system iterates over entities with certain components, defined in component_keys/0, and calls perform/1 on each entity. perform/1 should return the entity_pid when the entity should continue to exist in the shared collection.

Examples

# Define a service to display entities' names.
defmodule DisplayNames do
  @behaviour ECS.System

  # Accepts entities with a name component.
  def component_keys, do: [:name]

  def perform(entity) do
    # Displays the entity's name.
    IO.puts entity.name

    # Return the entity so that it is passed onto other systems.
    entity
  end
end

# Run entities through systems.
updated_entities = ECS.System.run([DisplayNames], entities)