Java 14 records canonical constructor

[Christian Beikov]

Hello,

I recently found out that a record constructor can set the record 
components explicitly and was kind of surprised. I thought that a record 
is a plain data carrier and that I can re-construct a record object from 
it's components, but this is not guaranteed.

Here a quick example:

public record UserRecord(Integer id, String userName) {
     public UserRecord {
         if (Character.isUpperCase(userName.charAt(0))) {
             this.userName = null;
         } else {
             this.userName = userName.toUpperCase();
         }
     }
}

IMO setting a field/record component directly should be prohibited. A 
developer should move such a logic to a static method or a different 
constructor. The canonical record constructor should only do sanity 
checks i.e. argument is not-null, not blank etc. but not alter the 
arguments or set the fields manually. It's ok for an additional 
non-canonical constructor to alter the arguments though.

What do you think? Was that an oversight or is this intended? If it is 
intended, what is the reasoning for allowing this?

I don't have a problem with this behavior. I just wouldn't have expected 
it. If I remember correctly, there were some talks about de-construction 
patterns at conferences that pointed out, that being able to 
re-construct a record from the component state is a vital property of 
records.

Regards,

Christian