newtype_index

rustc_index_macros

Macro newtype_index 

Source 
newtype_index!() { /* proc-macro */ }
Expand description

Creates a struct type S that can be used as an index with IndexVec and so on.

There are two ways of interacting with these indices:

  • The From impls are the preferred way. So you can do S::from(v) with a usize or u32. And you can convert back to an integer with u32::from(s).

  • Alternatively, you can use the methods S::new(v) and s.index() to create/return a value.

Internally, the index uses a u32, so the index must not exceed u32::MAX.

The impls provided by default are Clone, Copy, PartialEq, Eq, and Hash.

Accepted attributes for customization:

  • #[derive(HashStable_Generic)]/#[derive(HashStable)]: derives HashStable, as normal.
  • #[encodable]: derives Encodable/Decodable.
  • #[orderable]: derives PartialOrd/Ord, plus step-related methods.
  • #[debug_format = "Foo({})"]: derives Debug with particular output.
  • #[max = 0xFFFF_FFFD]: specifies the max value, which allows niche optimizations. The default max value is 0xFFFF_FF00.
  • #[gate_rustc_only]: makes parts of the generated code nightly-only.