java 15 record as generated immutable implementation

How about generating the immutable implementation of a given interface as a java 15 record (JEP 359)?

This would allow all the benefits of records to be combined with the greatness and ecosystem integration of immutables (in my case: mainly compatibility with mapstruct and openapi).

WDYT?

[mickroll]

Well, maybe what I really need is a builder for records. And thats already possible using @Builder.Constructor (https://immutables.github.io/factory.html)

Thanks for the discussion!

[mickroll]

I thought of something along the lines of:

Data object definition:

import com.fasterxml.jackson.databind.annotation.JsonDeserialize;
import javax.validation.constraints.NotEmpty;
import org.immutables.value.Value;

@Value.Immutable(record = true)
@Value.Style(get = { "get*", "is*" }, init = "set*", allParameters = true)
@JsonDeserialize(builder = ImmutableLoginAttemptUser.Builder.class)
public interface LoginAttemptUser {

  @NotEmpty
  String getUsername();

  @NotEmpty
  String getPassword();
}

Record-style implementation, generated by immutables:

@javax.annotation.processing.Generated("org.immutables.processor.ProxyProcessor")
public record ImmutableLoginAttemptUser(String username, String password)
    implements LoginAttemptUser {

  @JsonProperty("username")
  @Override
  public String getUsername() {
    return username;
  }

  @JsonProperty("password")
  @Override
  public String getPassword() {
    return password;
  }
  
  public static ImmutableLoginAttemptUser.Builder builder() {
    return new ImmutableLoginAttemptUser.Builder();
  }

  @Generated(from = "LoginAttemptUser", generator = "Immutables")
  public static final class Builder {
    [... same as before]
  }
}

Usage, bean-style (these getters need to be generated by immutables to fulfill interface declarations):

  var user = ImmutableLoginAttemptUser.builder().setUsername("foo").setPassword("bar").build();
  String x = user.getUsername() + ":" + user.getPassword();

The jackson json deserializer would use the builder in a similar way. The jackson json serializer would use the bean-style getters.

Usage, record-style (these ‘getters’ are generated by compiler):

  var user = ImmutableLoginAttemptUser.builder().setUsername("foo").setPassword("bar").build();
  String x = user.username() + ":" + user.password();

I think the overall behaviour of the generated records are the same in comparison to created immutable classes.

Note the restrictions of records (https://openjdk.java.net/jeps/395#Rules-for-record-classes), that is why i would recommend to enable usage of records on an opt-in basis via @Value.Immutable(record = true).