rust-patch

Patch structs with other structs

rust-patch allows you to avoid boilerplate code when implementing partial updates of Rust structs.
Simply define a patch struct containing a subset of your fields, derive the Patch trait, and specify the original struct using the #[patch] attribute.
Fields of a patch struct may either be of the same type T as in the original struct or Option<T>.
In the latter case, the field to be patched will be left unchanged if the corresponding field in the patch is None

This crate is no_std compatible.

Container attributes

#[patch = "..."]

Set target struct to be patched

use rust_patch::Patch;
struct Item { data: u32 }

#[derive(Patch)]
#[patch = "Item"]
struct ItemPatch { data: Option<u32> }

Field attributes

#[patch(direct)]

By default, any fields in the patch of type Option<T> will be applied as such:

if let Some(val) = patch.field {
    target.field = val;
} 

In some cases, e.g. when the field in the target struct is also an Option, this behavior is undesirable. The direct attribute makes it so that the field is treated like any other T, meaning it will be applied like this:

target.field = patch.field;

#[patch(as_option)]

This attribute also primarily changes the handling of Option types. Unlike with direct however, the original value will not be overwritten if the patch value is None.

if patch.field.is_some() {
    target.field = patch.field;
}

Example

use rust_patch::Patch;
use serde::Deserialize;

#[derive(PartialEq, Debug)]
struct User {
    id: String,
    display_name: String,
    email: String,
}

#[derive(Deserialize, Patch)]
#[patch = "User"]
struct UserPatch {
    display_name: Option<String>,
    email: Option<String>,
}

let user = User {
    id: "6bf25b70-bffa-49e0-905b-2d2e608e3abd".to_string(),
    display_name: "Max Mustermann".to_string(),
    email: "max.mustermann@example.org".to_string(),
};

let raw_patch = r#"{
    "id": "some invalid id",
    "email": "max.mustermann@example.com"
}"#;

let patch: UserPatch = serde_json::from_str(raw_patch).unwrap();
let patched_user = patch.apply(user);

// Since `id` is not part of our `UserPatch` struct it stays unchanged
assert_eq! {
    patched_user,
    User {
        id: "6bf25b70-bffa-49e0-905b-2d2e608e3abd".to_string(),
        display_name: "Max Mustermann".to_string(),
        email: "max.mustermann@example.com".to_string()
    }
};