java-lens

Automatic lens generation to support transformations to records.

Purpose

If you use records and you want to apply some transformation, code can get verbose, repetitive and error-prone. For example:

public record Person(String name, Address address, Address work, List<Person> friends) { }
public record Address(String street, int number, City city) implements LensOps<Address> { }
public record City(String name) { }

public static Person moveToNewYork(Person person) {
    Address address = original.address;
    var updatedCity = new City("New York");
    var updatedAddress = new Address(address.street, address.number, updatedCity);
    return new Person(person.name, updatedAddress, person.work, person.friends);
}

Using Lenses you can annotate your records, giving you a DSL to make specific changes:

public static Person moveToNewYork(Person person) {
    return PersonLens.µ
            .address()
            .city()
            .name()
            .with("New York")
            .apply(ALICE);
}

Usage

Add @Lenses annotation to your record(s)

@Lenses
public record Person(String name, Address address, Address work, List<Person> friends) { }

See Examples for more usage examples.

Development

Annotation Debugging

Run gradle compiler in debug mode

./gradlew --no-daemon -Dorg.gradle.debug=true clean build

Gradle process will wait for debugger to attach. Run IDE debugging process for port 5005.