# Lease Rs

**A std-ish primitive for temporary ownership transfer in Rust.**

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This crate provides a comprehensive solution for the fundamental problem of temporarily transferring ownership of values across scopes, closures, and async boundaries. It solves the "cannot borrow across `.await`" problem and enables scoped mutation patterns that are otherwise impossible in safe Rust.

## Installation

```toml
[dependencies]
lease-rs = "0.1"
```

For `no_std` environments (embedded, WASM, etc.):
```toml
lease-rs = { version = "0.1", default-features = false }
```

## Quick Start

```rust
use lease_rs::lease_async_mut;

async fn example() {
    let mut data = vec![1, 2, 3];

    let result = lease_async_mut(&mut data, |mut owned| async move {
        // You now have full ownership of the data across .await points
        tokio::time::sleep(tokio::time::Duration::from_millis(1)).await;
        owned.push(4);
        (owned, Ok("success"))
    }).await;

    assert_eq!(data, [1, 2, 3, 4]);
    assert_eq!(result, Ok("success"));
}
```

## Key Features

- **Zero-overhead by default** - Operations that can be zero-cost are zero-cost
- **Memory safety first** - Never compromise Rust's safety guarantees
- **Async cancellation safety** - Automatic restoration on tokio::select! cancellation
- **Explicit trade-offs** - All performance and safety trade-offs are visible to users
- **Complete API** - 11 functions covering all common use cases

## Quality Assurance

- **62 unit & doc tests** - 100% coverage
- **25M+ fuzz executions** - Zero crashes found
- **Memory safety verified** - Address sanitizer clean
- **CI/CD pipeline** - Automated testing on every PR

## Performance

**Most functions are zero-cost**. Only async mutable operations with cancellation safety have runtime cost:

- **Zero-cost** (9/11 functions): All owned variants and sync mutable variants
- **Non-zero-cost** (2/11 functions): `lease_async_mut`, `try_lease_async_mut` (require `T: Clone`)

## License

This project is licensed under either of
- Apache License, Version 2.0 ([LICENSE-APACHE](LICENSE-APACHE) or http://www.apache.org/licenses/LICENSE-2.0)
- MIT license ([LICENSE-MIT](LICENSE-MIT) or http://opensource.org/licenses/MIT)

at your option.