Realm generator rejects const values saying initialization must be const

[derrickgw]

What happened?

Using constant classes or negative numbers used to work for initialization. When upgrading from 1.6 to 2.0, this no longer works:

Field initializers must be constant

in: package:sustain/model/data/picture.dart:19:14
    ╷
16  │ @RealmModel()
17  │ class _Example {
    │       ━━━━━━━━ in realm model for 'Example'
... │
19  │   double y = -1;
    │              ^^ Must be const
    ╵
Ensure the default value for field "y" is const

Repro steps

Create a class with integer or float field and try to initialize it to a constant negative value.
Presumably this would work (or rather fail to work) with any other class that provides a const constructor.

Version

2.0.0

What Atlas Services are you using?

Local Database only

What type of application is this?

Flutter Application

Client OS and version

Linux

Code snippets

@RealmModel()
class _Example {
  double x = 0;
  double y = -1;
  int z = -1;
}

Stacktrace of the exception/crash you're getting

No response

Relevant log output

[SEVERE] realm:realm_generator on lib/model/data/picture.dart:

Field initializers must be constant

in: package:sustain/model/data/picture.dart:19:14
    ╷
16  │ @RealmModel()
17  │ class _Example {
    │       ━━━━━━━━ in realm model for 'Example'
... │
19  │   double y = -1;
    │              ^^ Must be const
    ╵
Ensure the default value for field "y" is const

[sync-by-unito]

➤ PM Bot commented:

Jira ticket: RDART-992

[Bilonik]

Hi,

Same issue here, any workaround?

[nirinchev]

We're aware of this and will address it with a future release. Currently, the only known mitigation is to downgrade to 1.6. I'm sorry for the regression.

[nielsenko]

Apparently -1 is not a literal to the Dart analyzer

[derrickgw]

True, but even if it was, checking for literals is not a good solution. Const variables are legal initializers, but are not literals.

…

On Wed, Mar 27, 2024, 04:51 Kasper Overgård Nielsen < ***@***.***> wrote: Apparently -1 is not a literal to the Dart analyzer — Reply to this email directly, view it on GitHub <#1606 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AGJZQCOKM3EMHJKIIPTR4Q3Y2KJALAVCNFSM6AAAAABFHRN6JSVHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHMZDAMRSGQ3DEMBZGA> . You are receiving this because you authored the thread.Message ID: ***@***.***>

[derrickgw]

That looks like a great improvement. Unfortunately there are still some cases that cause false errors. Here is an example:

import 'package:dart_numerics/dart_numerics.dart' as numerics;
const int myconst = 1;
@RealmModel(ObjectType.embeddedObject)
class $Test {
  ObjectId id = ObjectId();
  int value1 = myconst;
  int value2 = numerics.int64MinValue;
}

If I comment out the new const test, this generates legal dart.

[nielsenko]

@derrickgw Thank you for your observation. I have created #1612 to handle value1 and value2.

But this const check was added explicitly to disallow ObjectId id = ObjectId(), so that is still not allowed.

Consider:

@RealmModel()
class _Stuff {
  ObjectId id = ObjectId();
}

Which is legal with realm_generator 1.9.0. If you look at the generated class, you will find that is illegal because it lifts the initializer expression and uses it as the default value of the optional parameter id on the generated constructor.

Stuff({
    ObjectId id = ObjectId(), // <-- this is not valid Dart, as default values must be const
  }) {

[derrickgw]

Wow. That was super fast. Thanks.

I see now that ObjectId has a constructor body, and calls DateTime.now(), so it can't really become a const class.

The previous database code generator I migrated from had a different paradigm that generated a Schema class instead of a child class, which allowed non-const default values, but had other limitations.