Ensuring that all fields are present in constructor parameter list

Question

Is there a standard Dart-way of making sure that all fields of a class are present in a constructor parameter list?

A very simplified example:

class Message{
  String header;
  String body;
  DateTime sentAt;

  Message(this.header, this.body, this.sentAt);

  Message makeCopy(){
    return Message(header, body, sentAt);
  }
}

Now, a colleague comes along and adds the field String category, but forgets to add it to the constructor - and even worse, to the copy constructor. Is there a way to make the IDE (IntelliJ) issue a warning or error about this missing new field?

I'm thinking something similar to the warning issued when omitting an enum value from a switch-statement.

Or is there at least some way to make IntelliJ issue such a warning?

Probably possible with https://pub.dev/packages/pedantic – Karim Aug 20 '20 at 13:13 — Karim, Aug 20 '20 at 13:13

score 1 · Answer 1 · answered Aug 20 '20 at 14:10

You will get warnings or errors if you make your fields final, it seems from your class that it would be a good idea anyway.

Now... granted, that only moves that problem to "how do I ensure my colleague makes all new fields final, too".

To do that, you can declare you class @immutable and then analyzers can warn you.

Analyzers:

pub.dev/packages/pedantic
pub.dev/packages/effective_dart

A possible class declaration:

import 'package:meta/meta.dart';

@immutable
class Message {
  final String header;
  final String body;
  final DateTime sentAt;

  const Message(this.header, this.body, this.sentAt);

  Message makeCopy() {
    return Message(header, body, sentAt);
  }
}

Try adding a new field or removing one from the constructor, you will get errors.

score 0 · Answer 2 · answered Aug 20 '20 at 14:13

There is only one way but it is in most cases the correct way to go.

You make all fields final and enforce immutability which will lead to a compiler error if the field is not initialized in the constructor.

You can use the dartanalyzer to enforce the following rules or at least generate warnings. https://dart-lang.github.io/linter/lints/prefer_final_fields.html
https://dart-lang.github.io/linter/lints/prefer_const_declarations.html

To get started more easily with dartanalyzer you can look at the pedantic package or my preference lint.

Ensuring that all fields are present in constructor parameter list

2 Answers2