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

---
synopsis: "`inherit (x) ...` evaluates `x` only once"
prs: 9847
category: Fixes
credits: horrors
---

`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). (cherry picked from commit cefd0302b55b3360dbca59cfcb4bf6a750d6cdcf) Change-Id: Iff519f991adef2e51683ba2c552d37a3df7a179e 2024-03-08 08:52:15 +00:00			`---`
			synopsis: "`inherit (x) ...` evaluates `x` only once"
			`prs: 9847`
doc: add release note credits and categories for all the changes in Lix This does not add missing release notes, and it doesn't do anything about the profiles feature we would really like to have so we can have consistent credit. Change-Id: I72a6f7acfcff85f380be17dac76501a6f4693776 2024-05-15 02:14:58 +00:00			`category: Fixes`
			`credits: horrors`
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). (cherry picked from commit cefd0302b55b3360dbca59cfcb4bf6a750d6cdcf) Change-Id: Iff519f991adef2e51683ba2c552d37a3df7a179e 2024-03-08 08:52:15 +00:00			`---`

			`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.