Trait Prism 

pub trait Prism<S, A> {
    // Required methods
    fn preview(&self, whole: &S) -> Option<A>;
    fn set_if(&self, whole: &mut S, part: A) -> bool;
}

A prism for optional focusing (lens that may fail to view).

Unlike a lens, a prism’s preview returns Option<A> — the target may not exist. Useful for enum variants and optional fields.

Required Methods

fn preview(&self, whole: &S) -> Option<A>

Try to view the focused part. Returns None if the prism doesn’t match.

fn set_if(&self, whole: &mut S, part: A) -> bool

Set the focused part if the prism matches. Returns true if applied.

Dyn Compatibility

This trait is dyn compatible.

In older versions of Rust, dyn compatibility was called "object safety".

Implementors

impl<T: Clone> Prism<Option<T>, T> for SomePrism