Here goes my idea of an entity-component system written in C++. I’ve been using this in my home-made game engine, Wicked Engine for exactly a year now and I am still very happy with it. The focus is on simplicity and performance, not adding many features. This entity-component system (ECS from now on) is used to manage the game scene. That means storing game objects in memory, updating and rendering them, writing them to disk and loading them from disk to memory. The simple ECS that can handle these consists of: Entity: a unique identifier (a number). Imagine it like an ID in a database. Component: a data blob (a struct). This is the data that is associated with an entity. It is up to the user to create the data type, by creating a struct or a class in C++. System: data transformation (a function). This is any function that operates on a number of components. The user will write simple functions that take components as inputs and produce components as outputs. It is just any C++ function, really. ComponentManager: entity to component mapping container. Each entity can have one component held in it. The user can check if an entity and component exists, and query an entity’s component. This is the thing that we will implement here and give to the user as a tool to work with.

Entity: a unique identifier (a number). Imagine it like an ID in a database.
Component: a data blob (a struct). This is the data that is associated with an entity. It is up to the user to create the data type, by creating a struct or a class in C++.
System: data transformation (a function). This is any function that operates on a number of components. The user will write simple functions that take components as inputs and produce components as outputs. It is just any C++ function, really.
ComponentManager: entity to component mapping container. Each entity can have one component held in it. The user can check if an entity and component exists, and query an entity’s component. This is the thing that we will implement here and give to the user as a tool to work with.

The ECS will not only be simple, but performance is a big concern. We will want to have a lot of game objects, and manage them as fast as we can. Today, memory access is often the slow part of an application. The best way to avoid fetching memory and waiting for it to arrive, is to make good use of the cache and load from cache as often as we can. By keeping data in linear arrays, we are in a very good position, because most of the time we will iterate through every component and do something with them. The CPU is good at this when data is accessed linearly and memory can be prefetched into cache ahead of time. An other nice feature is that linear arrays will lend themselves very well to multithreading; you can use parallel for loops very simply and efficiently to process a large number of data. The ComponentManager will be responsible to manage components in a linear fashion. This is also called in many places Data Oriented Design (DoD)….

Source: https://wickedengine.net/2019/09/entity-component-system/

Entity-component system (ECS) used in my project Honeycrisp to manage entities and their components. Here is a link to the projects where I put this knowledge into practice: My Projects