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This shaves off a very significand amount of memory used for evaluation as well as reduces the GC-managed heap. Previously the union discriminator (InternalType) was stored as a separate field in the Value, which takes up whole 8 bytes due to padding needed for member alignment. This effectively wasted 7 whole bytes of memory. Instead of doing that InternalType is instead packed into pointer alignment niches. As it turns out, there's more than enough unused bits there for the bit packing to be effective. See the doxygen comment in the ValueStorage specialization for more details. This does not add any performance overhead, even though we now consistently assert the InternalType in all getters. This can also be made atomic with a double width compare-and-swap instruction on x86_64 (CMPXCHG16B instruction) for parallel evaluation.
Nix
Nix is a powerful package manager for Linux and other Unix systems that makes package management reliable and reproducible. Please refer to the Nix manual for more details.
Installation and first steps
Visit nix.dev for installation instructions and beginner tutorials.
Full reference documentation can be found in the Nix manual.
Building and developing
Follow instructions in the Nix reference manual to set up a development environment and build Nix from source.
Contributing
Check the contributing guide if you want to get involved with developing Nix.
Additional resources
Nix was created by Eelco Dolstra and developed as the subject of his PhD thesis The Purely Functional Software Deployment Model, published 2006. Today, a world-wide developer community contributes to Nix and the ecosystem that has grown around it.
- The Nix, Nixpkgs, NixOS Community on nixos.org
- Official documentation on nix.dev
- Nixpkgs is the largest, most up-to-date free software repository in the world
- NixOS is a Linux distribution that can be configured fully declaratively
- Discourse
- Matrix: #users:nixos.org for user support and #nix-dev:nixos.org for development
License
Nix is released under the LGPL v2.1.