lib/path/README.md: Justify returning subpaths

Co-authored-by: Valentin Gagarin <valentin.gagarin@tweag.io>
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Silvan Mosberger 2023-07-20 22:31:57 +02:00
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@ -187,6 +187,27 @@ Decision: All functions remove trailing slashes in their results.
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### Prefer returning subpaths over components
[subpath-preference]: #prefer-returning-subpaths-over-components
Observing: Functions could return subpaths or lists of path component strings.
Considering: Subpaths are used as inputs for some functions. Using them for outputs, too, makes the library more consistent and composable.
Decision: Subpaths should be preferred over list of path component strings.
<details>
<summary>Arguments</summary>
- (+) It is consistent with functions accepting subpaths, making the library more composable
- (-) It is less efficient when the components are needed, because after creating the normalised subpath string, it will have to be parsed into components again
- (+) If necessary, we can still make it faster by adding builtins to Nix
- (+) Alternatively if necessary, versions of these functions that return components could later still be introduced.
- (+) It makes the path library simpler because there's only two types (paths and subpaths). Only `lib.path.subpath.components` can be used to get a list of components.
And once we have a list of component strings, `lib.lists` and `lib.strings` can be used to operate on them.
For completeness, `lib.path.subpath.join` allows converting the list of components back to a subpath.
</details>
## Other implementations and references
- [Rust](https://doc.rust-lang.org/std/path/struct.Path.html)