Sundo - Snapshot Undo/Redo

A flexible and efficient undo/redo library for Rust, with first-class support for persistent data structures.

Features

• Generic undo/redo for any cloneable type
• Optimized for persistent data structures (im::Vector, im::HashMap, etc.)
• Transaction support with automatic rollback (RAII)
• History limits (count-based and memory-based) to prevent unbounded memory growth
• In-place updates with replace_current() for ephemeral state (navigation, UI state)
• Serialization support via snapshot export/import
• Builder pattern for flexible configuration
• Type-safe and ergonomic API
• Zero-cost abstractions when features aren't used

Installation

[dependencies]
sundo = "0.1.0"

Quick Start

Basic Usage

use sundo::{Actions, UndoRedo};

let mut undo_redo = UndoRedo::new();

// Push initial state
undo_redo.push(42, "Initial".to_string());

// Make changes
undo_redo.update(|x| x + 10, "Add 10".to_string());
undo_redo.update(|x| x * 2, "Multiply by 2".to_string());

// Undo and redo
assert_eq!(*undo_redo.present().unwrap(), 104);
undo_redo.undo();
assert_eq!(*undo_redo.present().unwrap(), 52);
undo_redo.redo();
assert_eq!(*undo_redo.present().unwrap(), 104);

With Persistent Data Structures

use sundo::{PersistentActions, PersistentUndoRedo};
use im::Vector;

let mut undo_redo = PersistentUndoRedo::new();

undo_redo.push(Vector::new(), "Empty".to_string());
undo_redo.update(|v| v.push_back(1), "Add 1".to_string());
undo_redo.update(|v| v.push_back(2), "Add 2".to_string());

// No Rc overhead - direct storage with structural sharing
let current = undo_redo.present().unwrap();
assert_eq!(current.len(), 2);

With History Limits

use sundo::UndoRedoBuilder;

// Count-based limit
let mut undo_redo = UndoRedoBuilder::new()
    .with_max_entries(100)  // Keep only last 100 states
    .build();

// Memory-based limit
let mut undo_redo = UndoRedoBuilder::new()
    .with_max_memory_mb(50)  // Keep up to 50 MB of history
    .build();

// Combined limits (whichever is hit first)
let mut undo_redo = UndoRedoBuilder::new()
    .with_max_entries(1000)
    .with_max_memory_mb(100)
    .build();

// Automatically prunes oldest entries when limit exceeded

With Transactions

use sundo::{Actions, UndoRedo, ScopedTransaction};

let mut undo_redo = UndoRedo::new();
undo_redo.push(0, "Initial".to_string());

{
    let mut tx = ScopedTransaction::begin(&mut undo_redo, "Batch update");
    tx.get().update(|x| x + 1, "temp".to_string());
    tx.get().update(|x| x + 2, "temp".to_string());
    tx.commit();  // Commits as single entry "Batch update"
}

// Or auto-rollback on error:
{
    let mut tx = ScopedTransaction::begin(&mut undo_redo, "Risky operation");
    tx.get().update(|x| x + 100, "temp".to_string());
    // If we panic or return early, transaction auto-rolls back
}

Ephemeral State Updates

For state changes that shouldn't be undoable (like navigation or UI state):

use sundo::{PersistentActions, PersistentUndoRedo};
use im::{HashMap, Vector};

#[derive(Clone)]
struct AppState {
    todos: Vector<String>,
    current_page: String,  // Navigation - shouldn't be undoable
}

let mut undo_redo = PersistentUndoRedo::new();
// ... add some todos (undoable) ...

// Change page without creating history entry
undo_redo.replace_current(|state| AppState {
    todos: state.todos.clone(),
    current_page: "Settings".to_string(),
});

// Undo still works on todos, navigation stays at Settings
undo_redo.undo();  // Reverts todo changes, keeps current_page

API Overview

Core Traits

• Actions<T> - Standard undo/redo operations with Rc wrapping
• PersistentActions<T> - Optimized for persistent data structures (no Rc)

Core Types

• UndoRedo<T> - Standard implementation for any cloneable type
• PersistentUndoRedo<T> - Optimized for im:: types

Builder Pattern

• UndoRedoBuilder<T> - Configure with capacity and limits
• PersistentUndoRedoBuilder<T> - Builder for persistent variant

Transactions

• ScopedTransaction - RAII transaction with auto-rollback
• PersistentScopedTransaction - Transaction for persistent types

Memory Estimation

• MemoryFootprint - Trait for memory-based history limits

Examples

See the demos/ directory for complete examples:

• basic-example - Comparison of standard vs persistent implementations
• persistent-example - Deep dive into persistent data structures
• scoped-transaction - Transaction patterns and error handling with RAII
• builder-pattern - History limits configuration
• memory-limits - Memory-based limits with MemoryFootprint trait
• mem-performance - Comprehensive memory performance testing and analysis
• serialization-example - Save/load history without serde
• delta-example - Compute diffs between history states
• todo_app - Full TUI todo application with undo/redo, transactions, save/load

Run demos with:

cd demos/basic-example && cargo run
cd demos/memory-limits && cargo run
cd demos/delta-example && cargo run
cd demos/todo_app && cargo run
# etc.

Note: All demos use the library via a local path dependency:

[dependencies]
sundo = { path = "../.." }

This is a good pattern for your own projects during development.

Design Philosophy

Memory Efficiency

For standard types, sundo uses Rc<T> to minimize memory overhead when cloning is expensive. For persistent data structures (which already use structural sharing), sundo stores values directly without the Rc layer.

Persistent Data Structures

When using im::Vector, im::HashMap, etc., the library leverages their built-in structural sharing. This means history entries share most of their data, making undo/redo memory-efficient even for large collections.

Zero-Cost Abstractions

• Builder pattern only allocates when configured
• History limits only check when set
• Transaction overhead is minimal (single Option field)

Documentation

• Usage Guide - for additional info

Generate API documentation locally:

cargo doc --open

Use Cases

• we will find out...

License

• MIT license (LICENSE-MIT or http://opensource.org/licenses/MIT)

Contributing

Contributions are welcome! Please feel free to submit a Pull Request.