Crate gecs

A generated entity component system 🦎

The gecs crate provides a compile-time generated, zero-overhead ECS for simulations on a budget. Unlike other ECS libraries, gecs takes a full ECS world structure definition from code and precompiles all queries to achieve better performance with no upfront cost or caching overhead. Queries in gecs can be inspected and checked at compile-time in order to catch what would otherwise be bugs presenting only in tests or execution. However, this comes at the cost of requiring all archetypes to be known and declared at compile-time, so that adding or removing components from entities at runtime isn’t currently possible – hybrid approaches could solve this in the future.

Archetypes in gecs can be set to contain a fixed capacity of entities. If all of the archetypes in your ECS world declaration are configured in this way, gecs will perform zero allocations after startup. This guarantees that your ECS world will adhere to a known and predictable memory overhead for constrained environments (e.g. servers on cloud instances). Attempting to create a new entity in a full archetype will return None (no panic). Support for dynamically-sized archetypes with Vec-like storage behavior is planned for support at a later date but is not currently implemented.

The goals for gecs are (in descending priority order):

• Fast iteration and find queries
• Fast entity creation and destruction
• Low, predictable memory overhead
• A user-friendly library interface
• Simplicity and focus in features

All of the code that gecs generates in user crates is safe, and users of gecs can use #[deny(unsafe_code)] in their own crates. Note that gecs does use unsafe code internally to allow for compiler optimizations around known invariants. It is not a goal of this library to be written entirely in safe Rust.

Getting Started

See the ecs_world!, ecs_find!, and ecs_iter! macros to get started.

Modules

• entity
  Handles for accessing entity representations as component data.
• error
  Error reporting for ECS operation failure.
• prelude
  use gecs::prelude::*; to import common macros, traits, and types.
• traits
  Traits for working with ECS types as generics.

Macros

• ecs_find
  Finds a single entity in an ECS world and performs an operation on it, if found.
• ecs_find_borrow
  Variant of ecs_find! that runtime-borrows data, for use with a non-mut world reference.
• ecs_iter
  Iterates over all entities across all archetypes that match the given component bounds.
• ecs_iter_borrow
  Variant of ecs_iter! that runtime-borrows data, for use with a non-mut world reference.
• ecs_world
  Macro for declaring a new ECS world struct with archetype storage.