Macro im::lens

macro_rules! lens {
    ( $from:ident : $headpath:ident : $headto:ident : $($tail:tt):* ) => { ... };
    ( $from:ident : $path:ident : $to:ident ) => { ... };
}

Construct a lens into a struct, or a series of structs.

You'll need to specify the type of the source struct, the name of the field you want a lens into, and the type of that field, separated by colons, eg. lens!(MyStruct: string_field: String). You can keep repeating name/type pairs for fields inside structs inside structs.

Please note: this only works on fields which are wrapped in an Arc (so the type of the string_field field in the example in the previous paragraph must be Arc<String>), and the source struct must implement Clone.

Examples

#[derive(Clone)]
struct Name {
    first: Arc<String>,
    last: Arc<String>
}

#[derive(Clone)]
struct Person {
    name: Arc<Name>
}

let person_last_name = lens!(Person: name: Name: last: String);

let the_admiral = Person {
    name: Arc::new(Name {
        first: Arc::new("Grace".to_string()),
        last: Arc::new("Hopper".to_string())
    })
};

assert_eq!(
    Arc::new("Hopper".to_string()),
    person_last_name.get(&the_admiral)
);