Crate merge2

Provides Merge trait that can be used to merge structs into single by it’s values:

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

Usage

The Merge trait can be used to merge two structs into single by values. The example use case is merging configuration from different sources: environment variables, multiple configuration files and command-line arguments, see the args.rs example.

Merge can be derived for structs. Also you can provide custom merge strategies for any fields that don’t implement Merge trait. A merge strategy is a function with the signature fn merge<T>(left: &mut T, right: &mut 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: 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, merge2 is a no_std.

Example

use merge2::Merge;

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

    // The strategy attribute is used to customize the merge behavior
    #[merge(strategy = ::merge2::vec::append)]
    pub groups: Vec<&'static str>,
}

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

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

Modules

any

Merge strategies applicable to any types

bool

Merge strategies for bool

hashmapstd

Merge strategies for HashMap

numnum

Merge strategies for numeric types

option

Merge strategies for Option

ord

Merge strategies for types that can be compared (PartialOrd)

stringstd

Merge strategies for String

vecstd

Merge strategies for Vec

Traits

Merge

A trait for objects that can be merged.

Derive Macros

Mergederive