Feedback on reconstruction: Hierarchy problems

[Remi Forax]

Hi Reiner,

> If you fully embrace immutable types, and you fully embrace hierarchies,
> withers are extremely unwieldy. Imagine the following setup:
> 
> record Movie {
>    int releaseYear;
>    String name;
>    Director director;
> }
> 
> record Director {
>    String name;
>    LocalDate dateOfBirth;
> }
> 
> record LocalDate {
>    int year, month, day;
> }
> 

Why you don't use the correct syntax of records here ?

And technically it's not a hierarchy (no inheritance) but more a delegation chain.


> and a movie:
> 
> Movie minorityReport = Movie.of("Minority Report", 2002,
> Director.of("Steven Spielberg", LocalDate.of(1946, 12, 18)));
> 
> With those examples in place, on to the problem: Let's say for some reason
> I need to modify Steven's birth year to 1956 instead. This utter disaster
> is the only way:
> 
> minorityReport.withDirector(minorityReport.getDirector().withDateOfBirth(minorityReport.getDirector().getDateOfBirth().withYear(1956)));
> 
> Oof. I don't immediately see anything in the strawman `with` syntaxes that
> would make this any better.
> 
> Lombok has recently introduced `@WithBy`, which tries to solve this by
> using lambdas. Here's how it would be done with lombok's @WithBy setup:
> 
> minorityReport.withDirectorBy(d -> d.withDateOfBirthBy(dob ->
> dob.withYear(1956)));
> 
> That is one of a number of ways to tackle the problem; one could also
> imagine solving this issue purely with syntax. Some strawman syntax could
> be:
> 
> minorityReport with { minorityReport.director.dateOfBirth.year = 1956 };
> 
> which arguably wins the readability syntax, and is the shortest snippet of
> them all.
> 
> I would like to see some solution (better than the disaster I started out
> with) to tackle wanting to make a change to a deeply nested element in an
> immutable hierarchy of types.

The proposed syntax is is very similar to @WithBy, it's a little mouthful but fine IMO

minorityReport = minorityReport with { director with { dateOfBirth with { year = 1956 }}};


> 
>  --Reinier Zwitserloot

Rémi