#patch #struct #macro-derive #derive #overlay #macro

macro struct-patch-derive

A library that helps you implement partial updates for your structs

25 releases (7 breaking)

0.8.6 Oct 2, 2024
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0.6.0 Jul 29, 2024
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Used in 3 crates (via struct-patch)

MIT license

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Struct Patch

Crates.io MIT licensed Docs

A lib help you patch Rust instance, and easy to partial update configures.

Introduction

This crate provides the Patch trait and an accompanying derive macro.

Deriving Patch on a struct will generate a struct similar to the original one, but with all fields wrapped in an Option.
An instance of such a patch struct can be applied onto the original struct, replacing values only if they are set to Some, leaving them unchanged otherwise.

Quick Example

use struct_patch::Patch;
use serde::{Deserialize, Serialize};

#[derive(Default, Debug, PartialEq, Patch)]
#[patch(attribute(derive(Debug, Default, Deserialize, Serialize)))]
struct Item {
    field_bool: bool,
    field_int: usize,
    field_string: String,
}

fn patch_json() {
    let mut item = Item {
        field_bool: true,
        field_int: 42,
        field_string: String::from("hello"),
    };

    let data = r#"{
        "field_int": 7
    }"#;

    let patch: ItemPatch = serde_json::from_str(data).unwrap();

    item.apply(patch);
    // You can do 
    // `let new_item = item << patch;`

    // For multiple patches,
    // you can do this
    // `let new_item = item << patch_1 << patch_2;`
    // or make an aggregated one, but please make sure the patch fields do not conflict, else will panic
    // ```
    // let overall_patch = patch_1 + patch_2 + patch_3;
    // let new_item = item << overall_patch;
    // ```

    assert_eq!(
        item,
        Item {
            field_bool: true,
            field_int: 7,
            field_string: String::from("hello")
        }
    );
}

Documentation and Examples

Also, you can modify the patch structure by defining #[patch(...)] attributes on the original struct or fields.

Struct attributes:

  • #[patch(name = "...")]: change the name of the generated patch struct.
  • #[patch(attribute(...))]: add attributes to the generated patch struct.
  • #[patch(attribute(derive(...)))]: add derives to the generated patch struct.

Field attributes:

  • #[patch(skip)]: skip the field in the generated patch struct.
  • #[patch(name = "...")]: change the type of the field in the generated patch struct.
  • #[patch(attribute(...))]: add attributes to the field in the generated patch struct.
  • #[patch(attribute(derive(...)))]: add derives to the field in the generated patch struct.

Please check the traits of document to learn more.

The examples demo following scenarios.

  • diff two instance for a patch
  • create a patch from json string
  • rename the patch structure
  • check a patch is empty or not
  • add attribute to patch struct
  • show option field behavior
  • show operators about patches

Features

This crate also includes the following optional features:

  • status(default): implements the PatchStatus trait for the patch struct, which provides the is_empty method.
  • op (default): provide operators << between instance and patch, and + for patches
    • default: when there is a field conflict between patches, + will add together if the #[patch(addable)] or #[patch(add=fn)] is provided, else it will panic.
    • merge (optional): implements the Merge trait for the patch struct, which provides the merge method, and << between patches.
  • std(optional):
    • box: implements the Patch<Box<P>> trait for T where T implements Patch<P>. This let you patch a boxed (or not) struct with a boxed patch.
    • option: implements the Patch<Option<P>> trait for Option<T> where T implements Patch<P>, please take a look at the example to learn more.
      • default: T needs to implement From<P>. When patching on None, it will based on from<P> to cast T, and this let you patch structs containing fields with optional values.
      • none_as_default: T needs to implement Default. When patching on None, it will patch on a default instance, and this also let you patch structs containing fields with optional values.
      • keep_none: When patching on None, it is still None.

Dependencies

~240–680KB
~16K SLoC