N.B. this crate requires nightly, as it makes use of Box<FnOnce> (unsized_locals) and untagged_unions.

thunk: Generic lazy evaluation for Rust

The thunk crate provides primitives for lazy evaluation in Rust.

At present, it provides five thunk types and three traits which abstract lazily evaluated types, LazyRef, LazyMut, and Lazy. The thunk types are as follows:

• Thunk: non-Send, non-Sync thunks.
• RcThunk: a reference-counted, cloneable thunk. An RcThunk<T> is essentially an Rc<Thunk<T>>; however, it implements Lazy.
• AtomicThunk: Send + Sync thunks which use atomic data internally. This is slower than Thunk, but AtomicThunk is thread-safe.
• ArcThunk: the Arc equivalent to RcThunk. Essentially an Arc<AtomicThunk<T>>.
• Strict: Send + Sync, paradoxically strict thunks. Strict doesn't actually defer anything, and is provided to make it simpler to write code which is generic over strictness.

The provided traits - LazyRef, LazyMut, and Lazy - abstract immutable references to lazy values, mutable references to lazy values, and owned lazy values, respectively. For example, Thunk implements LazyRef and LazyMut and Lazy; however, RcThunk only implements LazyRef. All traits take a lifetime parameter; this is a bandaid to cover Rust's current lack of associated lifetimes. This parameter bounds the lifetime of the closure object representing a deferred computation.

License

Licensed under either of

• Apache License, Version 2.0, (LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0)
• MIT license (LICENSE-MIT or http://opensource.org/licenses/MIT)

at your option.

Contribution

Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.