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 (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, 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
• bool
  Merge strategies for boolean types.
• hashmap
  Merge strategies for hash maps.
• option
  Merge strategies for Option
• ord
  Merge strategies for types that form a total order.
• string
  Merge strategies for strings.
• vec
  Merge strategies for vectors.

Traits

• Merge
  A trait for objects that can be merged.

Derive Macros

• Merge