# Designing a Paths Julep

**URL:** <https://discourse.julialang.org/t/designing-a-paths-julep/124335>\
**Category:** Internals & Design\
**Tags:** proposal, filesystem, path, rfc\
**Created:** [January 1, 2025, 12:37pm UTC](https://discourse.julialang.org/t/designing-a-paths-julep/124335 "2025-01-01T12:37:25Z")\
**Posts on this page:** 1\
**Showing post:** 73

<div class="post-metadata">

**Author:** ![jar1](https://avatars.discourse-cdn.com/v4/letter/j/c0e974/32.png) [@jar1](https://discourse.julialang.org/u/jar1)\
**Post date:** [January 6, 2025, 3:50am UTC](https://discourse.julialang.org/t/designing-a-paths-julep/124335/73 "2025-01-06T03:50:29Z")

</div>

(Reposting my Slack comment re relative paths.)

I had an idea, inspired by @ExpandingMan’s [decision](https://gitlab.com/ExpandingMan/FilePaths2.jl#why-disallow-relative-paths) in FilePaths2.jl to exclude relative paths.

The idea I like is having two types: `Path` which is always an absolute path and `PathSegment` which is an offset that can be concatenated to an `Path` or to a `PathSegment`, just like `Year` can be concatenated to a `Year` or to a `Date` .

I have two basic reasons.

**State.** Current working directory is global mutable state; I want to avoid a situation where runtime behavior depends on it. So if `p"foo"` expands to `Path("/home/user/src/proj/foo")` at compile time, then `cd` won’t affect the target as it’s already resolved to an absolute path.

**Semantics**. Path segments are common in real programs, and are semantically different from absolute paths. `Path("/etc/hosts")` has a lot of properties that `PathSegment("foo")` doesn’t have. Calling any filesystem methods on a path segment never makes sense and can only give wrong answers, which is a good indicator there are two different types living here.

Likewise there is often uncertainty over whether `"foo/bar"` is supposed to be relative to the current working directory or will be concatenated with a base path. For example `joinstring("/foo", "/bar") == "/foo/bar"` but `joinpath("/foo", "/bar") == "/bar"` which can be confusing but could be made to fail at compile time, as two absolute paths cannot be concatenated and relative path segments won’t override absolute base paths.

Separating the types simplifies a library author’s job since they know exactly what kind of object they receive from a caller, and likewise communicates to users what kind of object is expected from them.

---

_[View the full topic](https://discourse.julialang.org/t/designing-a-paths-julep/124335)._