Crate value_extra 

value-extra

A tri-state Patch<T> type for partial update semantics.

The Problem

When handling partial updates (PATCH requests, config merging, etc.), Option<T> conflates two distinct states:

• Field is absent → don’t touch the existing value
• Field is explicitly null → clear/reset the value

The Solution

Patch<T> provides three states:

• Patch::Some(T) — set the field to this value
• Patch::Empty — field was absent, leave unchanged
• Patch::None — field was explicitly null, clear it

Quick Start

use value_extra::Patch;

fn apply_name_patch(current: &mut Option<String>, patch: Patch<String>) {
    match patch {
        Patch::Some(new) => *current = Some(new),
        Patch::None => *current = None,
        Patch::Empty => {}
    }
}

Serde Usage

With the serde feature enabled:

#[derive(Deserialize, Serialize)]
struct UserPatch {
    #[serde(default, skip_serializing_if = "Patch::is_empty")]
    name: Patch<String>,
}

JSON Input	Patch State	Meaning
{ "name": "Alice" }	Patch::Some("Alice")	Set to value
{ "name": null }	Patch::None	Explicitly clear
{ }	Patch::Empty	Leave unchanged

Enums

Patch

A tri-state type for partial update semantics.