# Merge2
[](https://crates.io/crates/merge2)
[](https://docs.rs/merge2)
Provides `Merge` trait that can be used to merge structs into single by it's values:
```rust
trait Merge: Sized {
fn merge(&mut self, other: &mut Self);
}
```
`Merge` can be derived for structs:
```rust
use merge2::Merge;
#[derive(Merge)]
struct User {
#[merge(skip)]
pub name: &'static str,
pub location: Option<&'static str>,
#[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);
```
A merge strategy is a function with the signature `fn merge<T>(left: &mut T, right: &mut T)`
that merges `right` into `left`. The `merge2` 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:
environment variables, multiple configuration files and command-line
arguments, see the `args.rs` example.
## 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 for the `hashmap` and `vec`
that require the standard library. If this feature is not set,
`merge2` is a `no_std`.
### Based on the [source code](https://git.sr.ht/~ireas/merge-rs) of the `Merge` crate