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Diffstat (limited to 'doc/manual/rl-next/inherit-from-by-need.md')
| -rw-r--r-- | doc/manual/rl-next/inherit-from-by-need.md | 7 |
1 files changed, 7 insertions, 0 deletions
diff --git a/doc/manual/rl-next/inherit-from-by-need.md b/doc/manual/rl-next/inherit-from-by-need.md new file mode 100644 index 000000000..67c2cdedf --- /dev/null +++ b/doc/manual/rl-next/inherit-from-by-need.md @@ -0,0 +1,7 @@ +--- +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. |