Lib.rs

Fixed Type Id

Nightly toolchain required.

Make your types have a fixed type id and stable type name between different builds.

The crate provides a trait and a procedural macro. By implementing FixedTypeId, other crates can use [FixedTypeId::ty_id()], [FixedTypeId::ty_name()] and [FixedTypeId::ty_version()] to get the type id, name and version about this type

It use rapidhash to hash the type name you provided, with/without version hashed into the id. Then provide the hash as a fixed id for your type. So you can construct exact the same id from the same type name and version.

The purpose of this crate is to provide a fixed type id for simple types, which you may want to persist their metadata, like u8, i16, f32, str, String, bool, (u8,i16,f32), [u8; 3], [i16; 3], &[u8], etc. Or types frequently used in your structs, like HashMap<K, V>, Vec<T>, Box<T> etc.

It also support trait objects, which is used by trait_cast_rs to cast between different traits.

Note that the type name implemented by default for standard library types may be different from core::any::type_name, you shouldn't compare it with [FixedTypeId::ty_name()].

Because of the orphan rule, if you want to implement FixedTypeId for types in other crates, you can submit a PR to add them.

Usage

The example usage:

use fixed_type_id::{FixedTypeId, FixedId, fixed_type_id, name_version_to_hash};
use std::hash::Hasher;

mod m {
    // the macro use `self::xxx` to import required items, I avoid to use `$crate` because it avoid to reexport items from this crate.
    use fixed_type_id::{FixedTypeId, FixedId, fixed_type_id, FixedVersion};
    pub trait Q {}
    pub trait W {}
    pub trait E<T> {}
    fixed_type_id!{
        // default to (0,0,0)
        #[FixedTypeIdVersion((0,1,0))]
        // #[FixedTypeIdFile("types.toml")]
        // no default, but when store into file, version will be dropped, so only use it for debug.
        dyn m::Q; // type name is "dyn m::Q", it only store the type name you provided, without modification.
        dyn W; // type name is "dyn W", though `W` is under `m` module, it still store "dyn W"
        dyn E<u8>; // type name is "dyn E<u8>"
        A; // type name is "A"
        B<u8>; // type name is "B<u8>"
    }
    pub struct A;
    pub struct B<T> {
    pub t: T
    }
    impl Q for A {}
}
use m::*;
assert_eq!(<dyn Q>::TYPE_ID.0, name_version_to_hash("dyn m::Q", &(0,1,0).into()));
assert_eq!(<dyn Q>::TYPE_NAME, "dyn m::Q");
assert_eq!(<A as FixedTypeId>::TYPE_VERSION, (0,1,0).into());
assert_eq!(<A as FixedTypeId>::TYPE_NAME, "A");

If you want to define for your generic struct, you can use implement_wrapper_fixed_type_id:

use fixed_type_id::{FixedTypeId, FixedId, ConstTypeName, fstr_to_str, FixedVersion, implement_wrapper_fixed_type_id};
use std::ops::Add;

pub struct MyStruct<T: Add> {
    pub x: T,
}

implement_wrapper_fixed_type_id!{
    // You can define a typename with different module path, but it's not recommended.
    // Generally, you should define it in the same module as the struct for better readability.
    MyStruct<T:Add> => "SomeSpecialModule::MyStruct"
}

assert_eq!(<MyStruct<u8> as FixedTypeId>::TYPE_NAME, "SomeSpecialModule::MyStruct<u8>");

Also, you can define this trait yoursellf:

use fixed_type_id::{FixedTypeId, FixedId, FixedVersion};
use rapidhash::rapidhash;

struct MyType;

impl FixedTypeId for MyType {
    const TYPE_NAME: &'static str = "MyType";
    // make this type id hash without version
    const TYPE_ID: FixedId = FixedId::from_type_name(Self::TYPE_NAME, None);
    const TYPE_VERSION: FixedVersion = FixedVersion::new(0, 0, 0);
}

assert_eq!(<MyType as FixedTypeId>::TYPE_NAME, "MyType");
assert_eq!(<MyType as FixedTypeId>::TYPE_ID.0, rapidhash::rapidhash("MyType".as_bytes()));
assert_eq!(<MyType as FixedTypeId>::TYPE_VERSION, (0,0,0).into());

Notes

Version

For standard libraries types, the version is always (0,0,0), in the future, it may be changed to rustc version you are using.

Currently, this crate implement FixedTypeId for these types:

• (), Infallible
• T for all primitive types, like u8, i16, f32, str, String, bool etc.
• &T, &mut T for all primitive types
• Box<T>, Vec<T>, HashMap<K, V>, PhantomData<T>, NonZero<T>, fn(T) -> R, fn() -> R for all generic types that implement FixedTypeId
• (T,), (T,U), (T,U,V)... (T1,..., T16) for all generic types that implement FixedTypeId
• [T; N] for all T that implement FixedTypeId, but there is a limit for N, only N <= 32 or some special numbers(64, 128, 256,..., 768, 1024, 2048,...,65535) are supported, other numbers will just leave it as N. If you know how to generate &str for const N: usize in const context, you can submit a PR to add it.

Type Name Length

When you want to implement FixedTypeId for your types with generic parameters, you need to provide a dynamic generated &str as type name either 1. in const context or 2. store a &[&str] in const and then concat them at runtime.

If we choose to generate it in const context, because the only way i know to dynamically generate a &str in const context is to fill a fixed length array [u8;N], and this array will be persisted into the binary, so the length of the type name is limited by the binary size. Currently, the length can be configured by feature flags len64, len128 and len256, the default is len128, it means the max length of the type name is 128 bytes.

If we choose to store a &[&str] in const and then concat them at runtime, the return type of [FixedTypeId::ty_name()] will be String, it's different from the return type of core::any::type_name, which is &'static str. It makes it difficult to just replace core::any::type_name with type_name or [FixedTypeId::ty_name()].

So currently we choose to generate it in const context.

Differences between fixed_type_id, fixed_type_id_without_version_hash and random_fixed_type_id

• fixed_type_id: Generate a unique id for the type, with a FixedId that rapidhash::rapidhash the name you provided, the version is also hashed into the FixedId. Version defaults to (0,0,0), use #[FixedTypeIdVersion((0,1,0))] to change it. Use it when you want that different versions of your type have different ids.
• fixed_type_id_without_version_hash: Generate a unique id for the type, with a FixedId that rapidhash::rapidhash the name you provided, without version hashed into the FixedId. Use it when you want that different versions of your type have the same id.
• random_fixed_type_id: Generate a random id for the type, with a FixedId that random generated for each build.

All these macros can be used with:

• #[FixedTypeIdVersion((x,y,z))]: Set the version to (x,y,z).
• #[FixedTypeIdFile("filename.toml")]: Store the type id into a file, so you can use it for debug, make sure the file already exists.
• #[FixedTypeIdEqualTo("other_type")]: Make the type id FixedId equal to other_type, so the two types have the same id, but different type names, and versions.

Erase Type Name

It can be configured by feature flag erase_name, default is disabled.

Currently, it only works for implementation of FixedTypeId by fixed_type_id and fixed_type_id_without_version_hash.