Crate struct_patch

This crate provides the Patch and Filler traits and 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.

The following code shows how struct-patch can be used together with serde to patch structs with JSON objects.

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);

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

More details on how to use the the derive macro, including what attributes are available, are available under Patch

Deriving Filler on a struct will generate a struct similar to the original one with the field with Option, BTreeMap, BTreeSet, BinaryHeap,HashMap, HashSet, LinkedList, VecDeque or Vec. Any struct implement Default, Extend, IntoIterator, is_empty can be used with #[filler(extenable)]. Unlike Patch, the Filler only work on the empty fields of instance.

use struct_patch::Filler;

#[derive(Filler)]
struct Item {
    field_int: usize,
    maybe_field_int: Option<usize>,
}
let mut item = Item {
    field_int: 0,
    maybe_field_int: None,
};

let filler_1 = ItemFiller{ maybe_field_int: Some(7), };
item.apply(filler_1);
assert_eq!(item.maybe_field_int, Some(7));

let filler_2 = ItemFiller{ maybe_field_int: Some(100), };
item.apply(filler_2);
assert_eq!(item.maybe_field_int, Some(7));

Re-exports

pub use traits::*;

Modules

traits