Derive Macro Delta 

#[derive(Delta)]
{
    // Attributes available to this derive:
    #[delta_struct]
}

Derives Delta, generating a {Self}Delta struct that holds only the changed parts of a value plus the trait implementation that produces and applies one.

The generated type takes the visibility and generic parameters of the type it is derived on, and mirrors its shape: a tuple struct’s delta is a tuple struct with its fields in the same positions, and an enum’s is an enum with one variant per diffable source variant. A struct’s delta fields are all pub.

For an enum, Output is EnumDelta<Self, {Self}Delta> rather than the bare companion, because a value can change variant as well as change within one — and changing variant is a replacement rather than a difference.

See the delta-struct crate documentation for the full picture, including trait bounds, serde usage, and limitations; what follows is the attribute reference.

Container attributes

Attribute	Effect
default = "<field type>"	Field type for fields that don’t specify one. Defaults to "scalar".
delta_leader = "<tokens>"	Tokens emitted directly above the generated struct — derives, doc comments, anything.

Field attributes

Attribute	Effect
field_type = "<field type>"	How this field is diffed. Overrides the container’s default.
delta_leader = "<tokens>"	Tokens emitted directly above the generated field.

Field types

Each maps one source field onto exactly one delta field.

Value	Delta representation	Requires
"scalar"	delta_struct::ScalarDelta<T>	T: PartialEq
"unordered"	<T as Unordered>::Delta — BagDelta<Item> for a set, EntryDelta<Key, Value> for a map	T: Unordered
"unordered-delta"	MapDelta<Key, Value, <Value as Delta>::Output>, an add, a remove, and a change	T: IntoIterator + Extend<Item> + TryIndexMut<Key, Output = Value> Item: MapEntry (so (K, V)), Value: Delta
"ordered"	SeqDelta<Item>, a Myers edit script	T: IntoIterator + FromIterator<Item>, Item: Hash + Eq
"delta"	Option<<T as Delta>::Output>	T: Delta

Example

use delta_struct::Delta;

#[derive(Delta)]
#[delta_struct(delta_leader = "#[derive(Debug)]")]
struct Device {
    #[delta_struct(field_type = "unordered")]
    services: std::collections::HashSet<String>,
    online: bool,
}