Add index operator access to Expression. (#161)

* Add index operator access to Expression.

* Address feedback.

Author: matanlurey

CHANGELOG.md

@@ -1,7 +1,34 @@
-## 2.1.1-dev
+## 2.2.0-dev
 
 * Imports are prefixed with `_i1` rather than `_1` which satisfies the lint
-  `lowercase_with_underscores`.
+  `lowercase_with_underscores`. While not a strictly breaking change you may
+  have to fix/regenerate golden file-like tests. We added documentation that
+  the specific prefix is not considered stable.
+
+* Added `Expression.index` for accessing the `[]` operator:
+
+```dart
+void main() {
+  test('should emit an index operator', () {
+    expect(
+      refer('bar').index(literalTrue).assignVar('foo').statement,
+      equalsDart('var foo = bar[true];'),
+    );
+}  );
+
+  test('should emit an index operator set', () {
+    expect(
+      refer('bar')
+        .index(literalTrue)
+        .assign(literalFalse)
+        .assignVar('foo')
+        .statement,
+      equalsDart('var foo = bar[true] = false;'),
+    );
+  });
+}
+```
+
 * `literalList` accepts an `Iterable` argument.
 
 ## 2.1.0

lib/src/specs/expression.dart

@@ -45,6 +45,19 @@ abstract class Expression implements Spec {
     return new BinaryExpression._(expression, other, '&&');
   }
 
+  /// Returns accessing the index operator (`[]`) on `this`.
+  Expression index(Expression index) {
+    return new BinaryExpression._(
+      expression,
+      new CodeExpression(new Block.of([
+        const Code('['),
+        index.code,
+        const Code(']'),
+      ])),
+      '',
+    );
+  }
+
   /// This expression preceded by `await`.
   Expression get awaited {
     return new BinaryExpression._(

pubspec.yaml

@@ -1,5 +1,5 @@
 name: code_builder
-version: 2.1.1-dev
+version: 2.2.0-dev
 description: A fluent API for generating Dart code
 author: Dart Team <[email protected]>
 homepage: https://github.com/dart-lang/code_builder

test/specs/code/expression_test.dart

@@ -266,6 +266,35 @@ void main() {
     );
   });
 
+  test('should emit an index operator', () {
+    expect(
+      refer('bar').index(literalString('key')).assignVar('foo').statement,
+      equalsDart("var foo = bar['key'];"),
+    );
+  });
+
+  test('should emit an index operator set', () {
+    expect(
+      refer('bar')
+          .index(literalString('key'))
+          .assign(literalFalse)
+          .assignVar('foo')
+          .statement,
+      equalsDart("var foo = bar['key'] = false;"),
+    );
+  });
+
+  test('should emit a null-aware index operator set', () {
+    expect(
+      refer('bar')
+          .index(literalTrue)
+          .assignNullAware(literalFalse)
+          .assignVar('foo')
+          .statement,
+      equalsDart('var foo = bar[true] ??= false;'),
+    );
+  });
+
   test('should emit assigning to a var', () {
     expect(
       literalTrue.assignVar('foo'),