let mut x = (1, (2, (3, 4)));
*x.view_mut(optics!(_1._1._1)) *= 2;
assert_eq!(x.view(optics!(_1._1._1)), 8);

let mut x: (_, Result<_, ()>) = (1, Ok((2, 3)));
*x.preview_mut(optics!(_1.Ok._1))? *= 2;
assert_eq!(x.preview(optics!(_1.Ok._1))?, 6);

let mut x = (1, vec![Some((2, 3)), None]);
    x
    .traverse_mut(optics!(_1._mapped.Some._0))
    .into_iter()
    .for_each(|i| *i += 1);
assert_eq!(x.traverse(optics!(_1._mapped.Some._0)), vec![3]);

Some(())

} ```

derive lens for data types ```rust use lens_rs::*;

[derive(Review, Prism, Debug)]

enum AnEnum { A(T, i32), #[optic] B(T), }

[derive(Lens, Debug)]

struct Foo { #[optic] a: i32, #[optic] b: i32, }

fn test() -> Option<()> { let x = Review::review(optics!(Some.B), Foo { a: 3, b: 2, }); assert_eq!(x.preview(optics!(Some.B.b))?, 2);

Some(())

} ```

assume a type T may have substructure that the type is i32. ```rust fn bar>(t: &mut T, pm: Pm) { t.preview_mut(pm).map(|x| *x += 2); }

fn test() { let mut complex = (1, Ok((Err(2), 3))); bar(&mut complex, optics!(0)); bar(&mut complex, optics!(1.Err)); // do nothing bar(&mut complex, optics!(1.Ok.0.Ok)); // do nothing bar(&mut complex, optics!(1.Ok.0.Err)); bar(&mut complex, optics!(1.Ok.1)); assert_eq!(complex, (3, Ok((Err(4), 5)))); } ```

assume a type T must have a field .a. ```rust fn withfielda(t: &T) -> &str where T: LensRef { t.view_ref(optics!(a)) }

let foo = Foo { a: "this is Foo".tostring(), b: () }; let bar = Bar { a: "this is Bar".tostring(), c: 0 };

println!("{}", withfielda(foo)); println!("{}", withfielda(bar)); ```

Cargo.toml

add it in Cargo.toml

toml [package.metadata.inwelling] lens-rs = true