A fluent, builder-based library for generating valid Dart code.

Basic Usage

code_builder has a narrow and user-friendly API.

Most Dart syntax structures are created using builders. For example, an empty class:

final animal = Class((builder) => builder
    ..name = 'Animal'
    ..extend = refer('Organism')
);

Will produce:

class Animal extends Organism {}

If you're not a fan of nesting, you can create a builder directly and then call the build function. For example, adding a method to our class:

final method = MethodBuilder()
  ..name = 'eat'
  ..body = refer('print').call([literal('Yum!')]).statement // print('Yum!');
  ..lambda = true;

final animal = Class((builder) => builder
    ..name = 'Animal'
    ..extend = refer('Organism')
    ..methods.add(method.build()) // MethodBuilder -> Method
);

Will produce:

class Animal extends Organism {
  void eat() => print('Yum!');
}

Then, when finished, use a DartEmitter and the accept method to build the code_builder structures into valid Dart code. For example:

import 'package:dart_style/dart_style.dart';

// ... //

final emitter = DartEmitter();

// Generate code for 'animal' into a new StringBuffer 
final StringSink result = animal.accept(emitter);

// or, add it to an existing one
final buffer = StringBuffer();
animal.accept(emitter, buffer);

// format the output using package:dart_style
final String formatted = DartFormatter(
  languageVersion: DartFormatter.latestLanguageVersion)
    .format(result.toString());

// voilà
print(formatted);

Will output the code from above.

For more usage examples see the example and test folders.

Automatic Scoping

Have a complicated set of dependencies for your generated code? code_builder supports automatic scoping of your ASTs to automatically use prefixes to avoid symbol conflicts:

import 'package:code_builder/code_builder.dart';
import 'package:dart_style/dart_style.dart';

void main() {
  final library = Library((b) => b.body.addAll([
        Method((b) => b
          ..body = const Code('')
          ..name = 'doThing'
          ..returns = refer('Thing', 'package:a/a.dart')),
        Method((b) => b
          ..body = const Code('')
          ..name = 'doOther'
          ..returns = refer('Other', 'package:b/b.dart')),
      ]));

  // use a scoped DartEmitter to enable automatic prefixing
  // using Allocator.simplePrefixing
  final emitter = DartEmitter.scoped();

  final formatted = DartFormatter(
    languageVersion: DartFormatter.latestLanguageVersion)
        .format(library.accept(emitter).toString());

  print(formatted);
}

Will output:

import 'package:a/a.dart' as _i1;
import 'package:b/b.dart' as _i2;

_i1.Thing doThing() {}
_i2.Other doOther() {}

Contributing

• Read and help us document common patterns over in the docs.
• Is there a bug in the code? File an issue.

If a feature is missing (the Dart language is always evolving) or you'd like an easier or better way to do something, consider opening a pull request. You can always file an issue, but generally speaking, feature requests will be on a best-effort basis.

NOTE: Due to the evolving Dart SDK the local dartfmt must be used to format this repository. You can run it simply from the command-line:

dart run dart_style:format -w .

Updating generated (.g.dart) files

NOTE: There is currently a limitation in build_runner that requires a workaround for developing this package since it is a dependency of the build system.

Make a snapshot of the generated build_runner build script and run from the snapshot instead of from source to avoid problems with deleted files. These steps must be run without deleting the source files.

./tool/regenerate.sh