✓ Uses Rust 2018 edition
|0.1.1||Jun 22, 2019|
|0.1.0||Feb 17, 2019|
#251 in Algorithms
This is a library for easily comparing Rust data structures to detect differences. This is useful, for example, when reporting a test failure.
The simplest use case:
#[derive(Diff)]annotation on your type.
Now your error messages will highlight diffs instead of making you hunt for them manually.
See the API docs on the module for more.
Analyzing structural differences in Rust values using visitors.
This crate provides three functions that you can use immediately without having to learn a bunch of traits.
You can derive
Diff for any custom type that implements
This scheme is modeled after a combination of
serde::Serialize. There are two main traits:
Diffis implemented by types that can be diff'd.
Differis implemented by types that can process differences.
You'll typically derive
Diff. Derived impls will simply present the
structure of the type honestly, much like a derived
Debug impl would.
However, you can also implement it by hand if you need special
The most detailed docs are on the
Differ implement the Visitor Pattern for
climbing over a data structure. This is a little different than some other
applications of visitors you might have encountered. In particular:
The structure being visited is the Rust notion of types: here is a struct, the struct has fields, etc. A custom impl of
Diffcan fake the internals of a type to abstract away details, but the model is still the same.
Instead of visiting the parts of a single data structure, here we are visiting two data structures of the same type in parallel. This means we stop visiting if the structures diverge -- for example, if we discover two different variants of an
enumtype. (When this happens we notify the
The double dispatch aspect of the visitor pattern occurs at compile time, rather than at runtime, so there's very little overhead. The description of the pattern on Wikipedia (and the book Design Patterns that originated the name "visitor") doesn't discuss this version, only considering
dyn-style runtime dispatch.
This crate is
no_std compatible, in case you want to diff data structures
in a deeply-embedded system.