Lazy

Lazy evaluation in Rust.

Example

```rust fn expensive() -> uint { println!("I am only evaluated once!"); 7u }

fn main() { let a = lazy!(expensive());

// Thunks act like smart pointers!
assert_eq!(*a, 7u); // "I am only evaluated once." is printed here

let b = [*a, *a]; // Nothing is printed.
assert_eq!(b, [7u, 7u]);

} ```

API

lazy!($expr)

Expands to Thunk::new(proc() { $expr })

Thunk::new(proc() -> T)

Takes a proc, creates a delayed computation.

Thunk::force()

Forces the evaluation of the thunk so subsequent accesses are cheap. Values are stored unboxed.

Thunk::unwrap()

Consumes and forces the evaluation of the thunk and returns the contained value.

Thunk::deref() / Thunk::deref_mut()

Gets the value out of the thunk by evaluating the proc or grabbing it from the cache. Allows you to call methods on the thunk as if it was an instance of the contained valued through auto-deref.

There is also an equivalent API for SyncThunk, which is Sync + Send and usable for safe, concurrent laziness, except that they are created using sync_lazy! or by doing use Thunk = lazy::SyncThunk and using lazy!.