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Changelog

flecs

A fast entity component system (ECS) for C & C++

SanderMertens/flecs·

8.3k590CNOASSERTION

c99cpp11cpp14cpp17data-orienteddata-oriented-design+12

Last updated 3 months ago

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NewAugust 23, 2025

Flecs v4.1.1

Highlights

2x faster trivial set() calls (no hooks, observers or change detection)
5x faster trivial modified() calls (no hooks, observers or change detection)
3x faster prefab instantiation due to new component overriding design
Lots of reflection improvements for arrays, vectors and enums with custom underlying types
Lots of explorer improvements (better autocomplete, drag-to-change values in inspector, pane resizing, script saving and more!)
New script features that introduce more flexible ways to refer to entities:

// Create anonymous entity that is referred to later (previously impossible)
const alice: new {
  Position: {10, 20}
}

bob {
  // Alice variable can now be used without $ prefix
  (Likes, alice)
}

for i in 0..10 {
  "spaceship_{i}" { }

  "shuttle_{i}" {
    // Interpolated strings can now also be used in component/pair expressions
    (DockedTo, "spaceship_{i}")
  }
}

Release notes

This version includes the following bugfixes:

[cpp] Don't move lvalue during component assignment (thanks @ColoredCarrot!)

[cpp] Implement type traits in library to support older versions of gcc (thanks @AnonimiAngels!)
[cpp] Implement world::id_if_registered method
[cpp] Implement world::type_info()
[cpp] Remove redundant FLECS_META check for to_constant()
[cpp] Make world::to_json() methods const
[cpp] Allow using APIs that accept enum constants in builds with FLECS_CPP_NO_ENUM_REFLECTION
[core] Implement ecs_table_has_traversable() function
[core] Implement on_replace hook
[core] Don't emit OnSet events for operations when there are no hooks/observers
[core] Improve performance of set/ensure/emplace
[core] Remove redundant cr field from command struct
[core] Improve error messages
[core] Add checks that prevent making invalid modifications to core entities
[core] Change table_record_t.hdr.cache type to ecs_component_record_t
[core] Improve performance of component overriding
[core] Remove redundant New command
[core] Add new size argument to ecs_emplace_id and ecs_ensure_id
[core] Implement new Singleton trait
[core] Add more ecs_ref_t tests
[core] Turn setting both FLECS_DEBUG/NDEBUG error into warning
[core] Assert when passing alive ids to .entities member of ecs_bulk_desc_t
[meta] Split up push serializer operation into struct, array, vector
[meta] Split up opaque type serializer operation into value, struct, array, vector
[meta] Add underlying_kind field to serializer operation for serializing enums
[meta] Add constants field to serializer operation for serializing enums/bitmasks
[meta] Change meaning of ecs_member_t::count so that it's interpreted as inline array when >= 0
[meta] Split off constants member from EcsEnum/EcsBitmask into separate EcsConstants component
[meta] Split up meta addon code into smaller files
[json] Don't serialize schema to JSON for none fields
[script] Add script tests for CRLF line endings
[script] Don't reset script code for managed scripts after error
[script] Store errors on managed script
[script] Implement new expressions
[script] Implement exported variables
[script] Allow for using variable names without $ prefix as components, relationships and targets
[script] Allow for using interpolated string expressions as components
[script] Inheritance statements now require a scope
[rest] Allow managed scripts to be saved from the REST API/explorer
[rest] Always store build info on world so it is available for the explorer
[cmake] Bump cmake_minimum_required_version (thanks @niceEli!)
[docs] Fix issues in script examples
[docs] Remove outdated section on pipelines from system manual
[docs] Add Gloam vault to README
[docs] Fix source documentation for is_alive()/is_valid()
[docs] Fix query section in design with flecs manual
[docs] Fix broken link in quickstart (thanks @ZaddikDev!)
[docs] Add custom_serializer example
[docs] Fix issues in queries and prefab manual (thanks @Chetco!)
[docs] Fix outdated examples in change detection section of query manual
[docs] Update incorrect is_enabled to enabled in manuals (thanks @ericjeker!)
[docs] Add hooks section to entities and components manual