bjoernager/rust
bjoernager/rust
1
Fork 0
Code Activity

Document non-guarantees for Hash

Browse source 
Dependence on endianness and type sizes was reported for enum discriminants in #74215 but it is a more general
issue since for example the default implementation of `Hasher::write_usize` uses native endianness.
Additionally the implementations of library types are occasionally changed as their internal fields
change or hashing gets optimized.
This commit is contained in:
The8472 2021-11-18 02:00:53 +01:00
parent 934624fe5f
commit fd1494e9c3
1 changed files with 13 additions and 0 deletions
Download patch file Download diff file Expand all files Collapse all files

13
library/core/src/hash/mod.rs
View file

@ -164,6 +164,19 @@ mod sip;
/// `0xFF` byte to the `Hasher` so that the values `("ab", "c")` and `("a",
/// "bc")` hash differently.
///
/// ## Portability
///
/// Due to differences in endianness and type sizes data fed by `Hash` to a `Hasher`
/// should not be considered portable across platforms. Additionally the data passed by most
/// standard library types should not be considered stable between compiler versions.
///
/// This means tests shouldn't probe hard-coded hash values or data fed to a `Hasher` and
/// instead should check consistency with `Eq`.
///
/// Serialization formats intended to he portable between platforms or compiler versions should
/// either avoid encoding hashes or only rely on `Hash` and `Hasher` implementations that
/// provide additional guarantees.
///
/// [`HashMap`]: ../../std/collections/struct.HashMap.html
/// [`HashSet`]: ../../std/collections/struct.HashSet.html
/// [`hash`]: Hash::hash