nix-super/doc/manual/rl-next/inherit-from-by-need.md

---
synopsis: "`inherit (x) ...` evaluates `x` only once"
prs: 9847
---

`inherit (x) a b ...` now evaluates the expression `x` only once for all inherited attributes rather than once for each inherited attribute.
This does not usually have a measurable impact, but side-effects (such as `builtins.trace`) would be duplicated and expensive expressions (such as derivations) could cause a measurable slowdown.
evaluate inherit (from) exprs only once per directive desugaring inherit-from to syntactic duplication of the source expr also duplicates side effects of the source expr (such as trace calls) and expensive computations (such as derivationStrict). 2024-01-27 17:33:34 +02:00			`---`
			synopsis: "`inherit (x) ...` evaluates `x` only once"
			`prs: 9847`
			`---`

			`inherit (x) a b ...` now evaluates the expression `x` only once for all inherited attributes rather than once for each inherited attribute.
			This does not usually have a measurable impact, but side-effects (such as `builtins.trace`) would be duplicated and expensive expressions (such as derivations) could cause a measurable slowdown.