Crate merge

Provides Merge, a trait for objects that can be merged.

Usage

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

The Merge trait can be used to merge two objects of the same type into one. The intended use case is merging configuration from different sources, for example environment variables, multiple configuration files and command-line arguments, see the args.rs example.

This crate does not provide any Merge implementations, but Merge can be derived for structs. When deriving the Merge trait for a struct, you can provide custom merge strategies for the fields that don’t implement Merge. A merge strategy is a function with the signature fn merge<T>(left: &mut T, right: T) that merges right into left. The submodules of this crate provide strategies for the most common types, but you can also define your own strategies.

Features

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.

Example

use merge::Merge;

#[derive(Merge)]
struct User {
    // Fields with the skip attribute are skipped by Merge
    #[merge(skip)]
    pub name: &'static str,

    // The strategy attribute is used to customize 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"],
};
ferris.merge(defaults);

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

Modules

bool

Merge strategies for boolean types.

hashmap

Merge strategies for hash maps.

num

Merge strategies for numeric types.

option

Merge strategies for Option

ord

Merge strategies for types that form a total order.

vec

Merge strategies for vectors.

Traits

Merge

A trait for objects that can be merged.

Derive Macros

Merge