rust/compiler/rustc_index/src/idx.rs

use std::fmt::Debug;
use std::hash::Hash;

/// Represents some newtyped `usize` wrapper.
///
/// Purpose: avoid mixing indexes for different bitvector domains.
pub trait Idx: Copy + 'static + Eq + PartialEq + Debug + Hash {
    fn new(idx: usize) -> Self;

    fn index(self) -> usize;

    #[inline]
    fn increment_by(&mut self, amount: usize) {
        *self = self.plus(amount);
    }

    #[inline]
    #[must_use = "Use `increment_by` if you wanted to update the index in-place"]
    fn plus(self, amount: usize) -> Self {
        Self::new(self.index() + amount)
    }
}

impl Idx for usize {
    #[inline]
    fn new(idx: usize) -> Self {
        idx
    }
    #[inline]
    fn index(self) -> usize {
        self
    }
}

impl Idx for u32 {
    #[inline]
    fn new(idx: usize) -> Self {
        assert!(idx <= u32::MAX as usize);
        idx as u32
    }
    #[inline]
    fn index(self) -> usize {
        self as usize
    }
}