对象安全的哈希 trait

此 crate 提供了一个 DynHash trait，可用于 trait 对象。实现了标准库的 std::hash::Hash trait 的类型可以自动由 DynHash trait 对象使用。

示例

use dyn_hash::DynHash;

trait MyTrait: DynHash {
    /* ... */
}

// Implement std::hash::Hash for dyn MyTrait
dyn_hash::hash_trait_object!(MyTrait);

// Now data structures containing Box<dyn MyTrait> can derive Hash:
#[derive(Hash)]
struct Container {
    trait_object: Box<dyn MyTrait>,
}

在没有 dyn-hash crate 的情况下，一个 trait trait MyTrait: std::hash::Hash {...} 不会是对象安全的（dyn MyTrait）。

error[E0038]: the trait `MyTrait` cannot be made into an object
 --> src/main.rs:7:12
  |
7 |     let _: &dyn MyTrait;
  |            ^^^^^^^^^^^^ `MyTrait` cannot be made into an object
  |
note: for a trait to be "object safe" it needs to allow building a vtable to allow the call to be resolvable dynamically; for more information visit <https://doc.rust-lang.net.cn/reference/items/traits.html#object-safety>
 --> $SYSROOT/lib/rustlib/src/rust/library/core/src/hash/mod.rs
  |
  |     fn hash<H: Hasher>(&self, state: &mut H);
  |        ^^^^ ...because method `hash` has generic type parameters

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