cafkafk/nixpkgs
cafkafk/nixpkgs
1
0
Fork 0
Code Issues Pull requests Projects Releases Packages Wiki Activity Actions 2

module-system.chapter.md: Elaborate on extendModules performance

Browse source
This commit is contained in:
Robert Hensing 2023-04-16 19:44:18 +02:00
parent 5fac39307d
commit 8f02e95aff
1 changed files with 11 additions and 2 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

13
doc/module-system/module-system.chapter.md
View file

@ -75,11 +75,20 @@ A function similar to `evalModules` but building on top of the already passed [`
If you're familiar with prototype inheritance, you can think of the current, actual `evalModules` invocation as the prototype, and the return value of `extendModules` as the instance.
This functionality is also available to modules as the `extendModules` module argument.
::: {.note}
**Evaluation Performance**
`extendModules` returns a configuration that shares very little with the original `evalModules` invocation, because the module arguments may be different.
So if you have a configuration that has been (or will be) largely evaluated, almost none of the computation is shared with the configuration returned by `extendModules`.
The real work of module evaluation happens while computing the values in `config` and `options`, so multiple invocations of `extendModules` have a particularly small cost, as long as only the final `config` and `options` are evaluated.
If you do reference multiple `config` (or `options`) from before and after `extendModules`, evaluation performance is the same as with multiple `evalModules` invocations, because the new modules' ability to override existing configuration fundamentally requires constructing a new `config` and `options` fixpoint.
This functionality is also available to modules as the `extendModules` module argument.
:::
#### `_module` {#module-system-lib-evalModules-return-value-_module}