closures.md

Closures

Closures are, after all, Rc-managed objects. They are implemented in a manner of shared external objects, as each call fills a pending argument and "mutates" the state of a closure. Hence, Clone operations may be needed if the closure is shared. Otherwise, it is updated linearly.

Generally, a closure object consists of a function pointer and its context. The context refers to both the objects captured during closure creation and the objects that are incrementally passed into the closure.

Fixed-length closures

Fixed length closure, from which the context length is at most 16, will be compiled into a Thunk structure, where P is basically the tuple describing the parameter pack state of the closure.

pub struct Thunk<P: PartialParams, R> {
    code: fn(P::Full) -> R,
    params: P,
}

Such thunk will be packaged into Rc<dyn BoxedClosure<(P1, P2, ...), R> (a fat pointer) where P_i is the pending parameter type and R is the return type.

Notice that all P_i should be cloneable as provided by Rura's type system.

Context

Context will either be captured in a local object or using Rust's native closure capturing.