Merge trait for Rust
Create workspace for merge and merge_derive
Add homepage, documentation, readme to Cargo.toml
Fix formatting for merge_derive


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The merge crate provides the Merge trait that can be used to merge multiple values into one:

trait Merge {
    fn merge(&mut self, other: Self);

Merge can be derived for structs:

use merge::Merge;

struct User {
    // Fields with the skip attribute are skipped by Merge
    pub name: &'static str,

    // The strategy attribute is used to select the merge behavior
    #[merge(strategy = merge::option::overwrite_none)]
    pub location: Option<&'static str>,

    #[merge(strategy = merge::vec::append)]
    pub groups: Vec<&'static str>,

let defaults = User {
    name: "",
    location: Some("Internet"),
    groups: vec!["rust"],
let mut ferris = User {
    name: "Ferris",
    location: None,
    groups: vec!["mascot"],

assert_eq!("Ferris", ferris.name);
assert_eq!(Some("Internet"), ferris.location);
assert_eq!(vec!["mascot", "rust"], ferris.groups);

A merge strategy is a function with the signature fn merge<T>(left: &mut T, right: T) that merges right into left. The merge crate provides strategies for the most common types, but you can also define your own strategies.

The trait can be used to merge configuration from different sources, for example environment variables, multiple configuration files and command-line arguments, see the args.rs example.


This crate has the following features:

  • derive (default): Enables the derive macro for the Merge trait using the merge_derive crate.
  • num (default): Enables the merge strategies in the num module that require the num_traits crate.
  • std (default): Enables the merge strategies in the hashmap and vec modules that require the standard library. If this feature is not set, merge is a no_std library.

#Minimum Supported Rust Version

This crate supports Rust 1.36.0 or later.


For bug reports, patches, feature requests and other messages, please send a mail to ~ireas/public-inbox@lists.sr.ht (archive) using the [merge-rs] prefix in the subject.

You can submit patches using git send-email, for example:

git send-email --to=~ireas/public-inbox@lists.sr.ht --subject-prefix="PATCH merge-rs"

Please prefix the subject with PATCH merge-rs so that CI will be automatically run.


This project is dual-licensed under the Apache-2.0 and MIT licenses. The documentation and configuration files contained in this repository are licensed under the Creative Commons Zero license. You can find a copy of the license texts in the LICENSES directory.

merge-rs complies with version 3.0 of the REUSE specification.