type_hash

Generate a hash for a Rust type.

The primary use-case for this crate is for detecting differences in message types between versions of a crate.

The TypeHash trait is implemented for most built-in types and a derive macro is provided, for implementing it for your own types.

Examples

```rust use type_hash::TypeHash;

[derive(TypeHash)]

pub enum Message { LaunchMissiles { destination: String }, CancelMissiles, }

fn main() { let hash = Message::typehash(); // this will only change if the type definition changes asserteq!(hash, 11652809455620829461); } ```

Customising derived TypeHash implementations

#[type_hash(foreign_type)]

If a struct field has a foreign type that does not implement TypeHash, you can mark it as a foreign type and the derive TypeHash implementation will use the name of the type in the hash instead. You need to be a little bit careful here because a change in the third party crate could change your type in an undetectable way.

```rust

[derive(TypeHash)]

pub struct MyStruct { #[typehash(foreigntype)] data: ArrayVec<[u16; 7]> } ```

#[type_hash(skip)]

Skip a field, so it is not part of the hash.

```

[derive(TypeHash)]

pub struct MyStruct { #[typehash(skip)] notimportant: Vec, } ```

#[type_hash(as = "...")]

Hash a field as if it had a different type. This allows you to change the type of a field to a different type that is still compatible for your application, without affecting the hash.

```

[derive(TypeHash)]

pub struct MyStruct { #[type_hash(as = "HashSet")] numbers: BTreeSet, } ```