imagicthecat/lua-emgr

emgr

Table of Contents

• Concept
  • Entity
  • Manager
• API

emgr, or Entity Manager, is a simple Lua library which implements a paradigm similar to Entity Component System (ECS).

The main difference with ECS is that the Component and System concepts are merged into the Manager.

See src.

Concept

Entity

An entity is a table which is a set of managers, defining a composition. It also has some methods and will free itself from managers on garbage collection.

Operations and data are not owned by an entity; its role is to bind managers to an object with automatic memory management.

Manager

A manager can be anything implementing the manager interface (methods). It defines and manages a component for the entities.

Operations can be implemented by managers, maybe depending on other managers, or functions processing entities and multiple managers, etc.

⚠️	To ensure proper garbage collection, init() / free() should be called from the entity and the manager must not have a strong reference to entities just to manage the internal data.

API

-- Create an entity.
emgr.entity()

-- Entity.

-- Initialize the entity into a manager.
-- Can be called even if already initialized.
entity:init(manager, ...)

-- Free the entity from a manager.
-- Can be called even if already freed.
entity:free(manager)

-- Check if the entity has a manager as composition (i.e. is managed by a manager).
-- Low-level alternative: check `entity[manager]`
entity:has(manager)

-- Manager interface, called by corresponding entity methods.

manager:__init(entity, ...)
manager:__free(entity)

Example 1. Getting managers from an entity.

for manager in pairs(entity) do ... end