Trait Lens 

pub trait Lens<S, A> {
    // Required methods
    fn view(&self, whole: &S) -> A;
    fn set(&self, whole: &mut S, part: A);

    // Provided methods
    fn over(&self, whole: &mut S, f: impl FnOnce(A) -> A)
       where A: Clone { ... }
    fn then<B, L2: Lens<A, B>>(self, inner: L2) -> Composed<Self, L2, A>
       where Self: Sized,
             A: Clone { ... }
}

A bidirectional lens focusing on part A of a whole S.

Laws

A well-behaved lens satisfies:

1. GetPut: lens.set(s, lens.view(s)) leaves s unchanged.
2. PutGet: After lens.set(s, a), lens.view(s) returns a.

Required Methods

fn view(&self, whole: &S) -> A

View the focused part.

fn set(&self, whole: &mut S, part: A)

Set the focused part, mutating the whole in place.

Provided Methods

fn over(&self, whole: &mut S, f: impl FnOnce(A) -> A)

where A: Clone,

Modify the focused part with a function.

fn then<B, L2: Lens<A, B>>(self, inner: L2) -> Composed<Self, L2, A>

where Self: Sized, A: Clone,

Compose this lens with an inner lens to focus deeper.

Dyn Compatibility

This trait is not dyn compatible.

In older versions of Rust, dyn compatibility was called "object safety", so this trait is not object safe.

Implementors

impl<A: Clone, B: Clone> Lens<(A, B), A> for Fst

impl<A: Clone, B: Clone> Lens<(A, B), B> for Snd

impl<S, A, G, P> Lens<S, A> for FieldLens<G, P>

where G: Fn(&S) -> A, P: Fn(&mut S, A),

impl<S, B, A, L1, L2> Lens<S, A> for Composed<L1, L2, B>

where L1: Lens<S, B>, L2: Lens<B, A>, B: Clone,

impl<S: Clone> Lens<S, S> for Identity

impl<T: Clone> Lens<Vec<T>, T> for AtIndex