3 releases
Uses old Rust 2015
0.1.4 | Jun 19, 2018 |
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0.1.3 |
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0.1.2 | Jun 4, 2018 |
0.1.1 | Jun 3, 2018 |
#26 in #usize
10KB
120 lines
typed_index_derive
Custom derive to easily create newtype index types.
A frequent pattern in Rust is to store objects in a vector and use integer indexes
as handlers to them. While using usize
works, it could become confusing if there
are several flavors of indexes. To make the meaning of each index clear the newtype
wrappers like FooIdx(usize)
are useful, but require a fair amount of boilerplate.
This crate derives the boilerplate for you:
#[macro_use]
extern crate typed_index_derive;
struct Spam(String);
#[derive(
// Usual derives for plain old data
Debug, Copy, Clone, Ord, PartialOrd, Eq, PartialEq, Hash,
// this crate
TypedIndex
)]
#[typed_index(Spam)] // index into `&[Spam]`
struct SpamIdx(usize); // could be `u32` instead of `usize`
fn main() {
let spams = vec![Spam("foo".into()), Spam("bar".into()), Spam("baz".into())];
// Conversions between `usize` and `SpamIdx`
let idx: SpamIdx = 1.into();
assert_eq!(usize::from(idx), 1);
// We can index `Vec<Spam>` with SpamIdx
assert_eq!(&spams[idx].0, "bar");
// However, we can't index `Vec<usize>`
// vec![1, 2, 3][idx]
// error: slice indices are of type `usize` or ranges of `usize`
// You can add/subtract `usize` from an index
assert_eq!(&spams[idx - 1].0, "foo");
// The difference between two indices is `usize`
assert_eq!(idx - idx, 0usize);
}
Dependencies
~2MB
~47K SLoC