use enum for EventType or assert them inside methods

[m1-nann]

Since we are using Dart, could we use enum instead of raw String? It's less error-prone, help avoiding typo
it would be something like this

ref.on(EventType.child_added, (snap) => {
  ///do something
})

Or at least we could assert if eventType is valid inside the methods

[pulyaevskiy]

I think enum fits well in this case. Only thing is that we should name values without underscores to comply with Dart style guide, e.g. EventType.childAdded.

Note that it would be a breaking change so would have to be released as 2.0.0 which for such a small change might be hard to justify major version bump.

We can approach this in two steps:

1. Add assertions as per your second suggestions, this would be non breaking. We can also add an abstract class with constants so that users are not forced to hard code strings. E.g.:

abstract class EventType {
  static const String childAdded = 'child_added';
  // ... etc
}

Would be nice to update examples and dartdocs to refer to these constants so that it's easier to discover.

All of this is non-breaking and we can release it in 1.x.x.

2. When we gather enough breaking changes or there is upstream (JS SDK) change that requires us to bump major version to 2.0.0 we can replace the abstract class with an enum and update all method signatures accordingly.

How does this sound?

[m1-nann]

naming: if we are not using the firebase string name child_added, I suggest considering uppercase low dash (ie. CHILD_ADDED). Maybe it's just a personal preference, though it's also used for firebase.database.ServerValues.TIMESTAMP.

I understand the possible breaking changes, so the two steps are pretty good ideas.

[pulyaevskiy]

Here is portion of official Dart style guide re: naming constants and enum values:
https://www.dartlang.org/guides/language/effective-dart/style#prefer-using-lowercamelcase-for-constant-names :

In new code, use lowerCamelCase for constant variables, including enum values.

I'd prefer to stick to the style guide as it makes this Dart code consistent with most of the Dart code available on Pub and the Dart SDK itself.

[m1-nann]

Oh, I see. I was searching for 'constant' and 'enum' but didn't catch it somehow. My bad.

[pulyaevskiy]

FYI: I added EventType with constants as per discussion and released together with your change of the on method as 1.2.0.