Struct IndexVec

#[repr(transparent)]
pub struct IndexVec<I, T>
where
    I: Idx,
{
    pub raw: Vec<T>,
    _marker: PhantomData<fn(&I)>,
}

An owned contiguous collection of Ts, indexed by I rather than by usize.

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.

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.

This allows to index the IndexVec with the new index type.

Fields

raw: Vec<T>

_marker: PhantomData<fn(&I)>