Introducing enum_class.dart

[David Morgan ☯]

Hi Dartisans,

For those who like a bit of class in their enums, or a bit of enum in their classes, a tool:

https://github.com/google/enum_class.dart

You write a class, declare the constants, and it generates the boilerplate needed for enum-like behaviour.

Example class that you write:

  https://github.com/google/enum_class.dart/blob/master/example/lib/test_enum.dart

Example generated code:

  https://github.com/google/enum_class.dart/blob/master/example/lib/test_enum.g.dart

Example project structure, note the "tools/build.dart":

  https://github.com/google/enum_class.dart/tree/master/example

The source_gen library is still bleeding edge, you'll need to be on SDK 1.12 to use enum_class.

Feedback welcome! I'm really interested in whether people find this useful and how we can make it more usable.

Although the implementation is bleeding edge, the idea is well tested: we have a similar tool and over a hundred of these semi-generated enums on my (Google internal) project.

Cheers

Morgan

[Daniel Joyce]

Richer enums like Java would be nice. Its rare, but I've found them handy.

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Daniel Joyce

The meek shall inherit the Earth, for the brave will be among the stars.

[David Morgan ☯]

Yes, I hope they end up in some future version of Dart.

In the meantime, enum_class is actually exactly designed to match Java functionality. On my project we keep Java and Dart equivalents for the same enum, and use them in RPCs. So we want the Dart enums to be able to carry code / implement interfaces, like the Java ones.

A quick look at the big picture / master plan:

 + built_collection.dart: released and stable, immutable collections with the builder pattern

 + enum_class.dart: just released, Java-like enums

 + built_value.dart: coming soon, codegen to help build nice immutable value types

 + built_json.dart: coming a bit later :) ... JSON serialization for all of the above: collections, enums, values

 + Built JSON for Java: Java equivalent serialization so you can use all of the above for RPCs; on the Java side you'll use @AutoValue

Cheers

Morgan

[Lasse Damgaard]

I actually miss full blown enums a lot in frontend code. 

Typical scenarios are:

 - Defining a sort order.

 - Converting values to a pretty print display string and vice versa.
 - Converting to/from JSON from my backend.

Doing all of this stuff in utility methods outside of the enum is ugly and means I'm always torn between whether to use enums or not.

 Lasse

[David Morgan ☯]

Exactly.

My approach is to forbid the use of native Dart enums.

By using native enums you create a trap for developers. If someone wants to add functionality to a native enum they might be lazy and just add utility method, when the correct thing is to convert to a class. So, start with a class and get it right from the start.

BTW, there's one more feature coming to enum_class, for Angular developers: we can generate a mixin class for you to mix in to your component class. It will expose the enum constants to your template so you can use them directly in the template.