Annotation Type WithBy

Put on any field to make lombok build a 'withBy' - a withFieldNameBy method which produces a clone of this object (except for 1 field which gets a new value).

Complete documentation is found at the project lombok features page for @WithBy.

Example:

     private @WithBy final int foo;
     private @WithBy final String bar;
 

will generate:

     public SELF_TYPE withFooBy(@lombok.NonNull IntUnaryOperator operator) {
         int foo = operator.apply(this.foo);
         return this.foo == foo ? this : new SELF_TYPE(foo, bar);
     }
     public SELF_TYPE withBarBy(@lombok.NonNull Function<? super String, ? extends String> operator) {
         String bar = operator.apply(this.bar);
         return this.bar == bar ? this : new SELF_TYPE(foo, bar);
     }
 

This annotation can also be applied to a class, in which case it'll be as if all non-static fields that don't already have a WithBy annotation have the annotation.

This annotation is primarily useful for hierarchical immutable data structures. For example:

     class Movie {
         @WithBy private final Director director;
     }
     
     class Director {
         @WithBy private final LocalDate birthDate;
     }
 

Using plain old @With, to increment a movie's director's birth date by one, you would write:

     movie = movie.withDirector(movie.getDirector().withBirthDate(movie.getDirector().getBirthDate().plusDays(1)));
 

but with @WithBy, you'd write:

     movie = movie.withDirectorBy(d -> d.withBirthDateBy(bd -> bd.plusDays(1)));