mikros/rust
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

Rollup merge of #122015 - dev-ardi:master, r=nnethercote

Browse Source 
Add better explanation for `rustc_index::IndexVec`

I feel like I didn't do a great job explaining what this does in https://github.com/rust-lang/rust/pull/119800, so this PR tries to give an example of why and how you would use it.

Addresses #93792.
This commit is contained in:
Matthias Krüger 2024-03-07 00:57:39 +01:00 committed by GitHub
commit d451faaab2
No known key found for this signature in database
GPG Key ID: B5690EEEBB952194
1 changed files with 18 additions and 1 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

19
compiler/rustc_index/src/vec.rs
View File

@ -12,7 +12,24 @@
use crate::{Idx, IndexSlice};
/// An owned contiguous collection of `T`s, indexed by `I` rather than by `usize`.
/// Its purpose is to avoid mixing indexes.
///
/// ## Why use this instead of a `Vec`?
///
/// An `IndexVec` allows element access only via a specific associated index type, meaning that
/// trying to use the wrong index type (possibly accessing an invalid element) will fail at
/// compile time.
///
/// It also documents what the index is indexing: in a `HashMap<usize, Something>` it's not
/// immediately clear what the `usize` means, while a `HashMap<FieldIdx, Something>` makes it obvious.
///
/// ```compile_fail
/// use rustc_index::{Idx, IndexVec};
///
/// fn f<I1: Idx, I2: Idx>(vec1: IndexVec<I1, u8>, idx1: I1, idx2: I2) {
/// &vec1[idx1]; // Ok
/// &vec1[idx2]; // Compile error!
/// }
/// ```
///
/// While it's possible to use `u32` or `usize` directly for `I`,
/// you almost certainly want to use a [`newtype_index!`]-generated type instead.