Improve enum decoding -- alternative with binary search instead of map lookup

protobuf/lib/src/protobuf/protobuf_enum.dart

@@ -2,21 +2,25 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// ignore_for_file: non_constant_identifier_names
+
 part of '../../protobuf.dart';
 
 /// A base class for all proto enum types.
 ///
-/// All proto `enum` classes inherit from [ProtobufEnum]. For example, given
-/// the following enum defined in a proto file:
+/// All proto `enum` classes inherit from [ProtobufEnum]. For example, given the
+/// following enum defined in a proto file:
 ///
-///     message MyMessage {
-///       enum Color {
-///         RED = 0;
-///         GREEN = 1;
-///         BLUE = 2;
-///       };
-///       // ...
-///     }
+/// ```
+/// message MyMessage {
+///   enum Color {
+///     RED = 0;
+///     GREEN = 1;
+///     BLUE = 2;
+///   };
+///   // ...
+/// }
+/// ```
 ///
 /// the generated Dart file will include a `MyMessage_Color` class that extends
 /// `ProtobufEnum`. It will also include a `const MyMessage_Color` for each of
@@ -37,16 +41,39 @@ class ProtobufEnum {
   /// Creates a new constant [ProtobufEnum] using [value] and [name].
   const ProtobufEnum(this.value, this.name);
 
-  /// Creates a Map for all of the [ProtobufEnum]s in [byIndex], mapping each
-  /// [ProtobufEnum]'s [value] to the [ProtobufEnum].
-  static Map<int, T> initByValue<T extends ProtobufEnum>(List<T> byIndex) {
-    final byValue = <int, T>{};
-    for (final v in byIndex) {
-      byValue[v.value] = v;
+  /// @nodoc
+  static List<T?> $_initDenseList<T extends ProtobufEnum>(List<T> byIndex) {
+    if (byIndex.isEmpty) return [];
+    final byValue = List<T?>.filled(byIndex.last.value + 1, null);
+    for (final enumValue in byIndex) {
+      byValue[enumValue.value] = enumValue;
     }
     return byValue;
   }
 
+  /// @nodoc
+  static List<T> $_initSparseList<T extends ProtobufEnum>(List<T> byIndex) =>
+      byIndex.toList()..sort((e1, e2) => e1.value.compareTo(e2.value));
+
+  /// @nodoc
+  static T? $_binarySearch<T extends ProtobufEnum>(
+      List<T> sortedList, int value) {
+    var min = 0;
+    var max = sortedList.length;
+    while (min < max) {
+      final mid = min + ((max - min) >> 1);
+      final element = sortedList[mid];
+      final comp = element.value.compareTo(value);
+      if (comp == 0) return element;
+      if (comp < 0) {
+        min = mid + 1;
+      } else {
+        max = mid;
+      }
+    }
+    return null;
+  }
+
   /// Returns this enum's [name] or the [value] if names are not represented.
   @override
   String toString() => name == '' ? value.toString() : name;

protoc_plugin/lib/protoc.dart

@@ -1,5 +1,6 @@
 import 'dart:convert';
 
+import 'package:collection/collection.dart';
 import 'package:protobuf/protobuf.dart';
 
 import 'const_generator.dart' show writeJsonConst;

protoc_plugin/lib/src/enum_generator.dart

@@ -165,7 +165,6 @@ class EnumGenerator extends ProtobufContainer {
         }
       }
       out.println();
-
       out.println('static const $coreImportPrefix.List<$classname> values ='
           ' <$classname> [');
       for (final val in _canonicalValues) {
@@ -175,11 +174,31 @@ class EnumGenerator extends ProtobufContainer {
       out.println('];');
       out.println();
 
-      out.println(
-          'static final $coreImportPrefix.Map<$coreImportPrefix.int, $classname> _byValue ='
-          ' $protobufImportPrefix.ProtobufEnum.initByValue(values);');
-      out.println('static $classname? valueOf($coreImportPrefix.int value) =>'
-          ' _byValue[value];');
+      var useList = _canonicalValues.isEmpty;
+      if (_canonicalValues.isNotEmpty) {
+        if (_canonicalValues.every((val) => !val.number.isNegative)) {
+          if (_canonicalValues.length / (_canonicalValues.last.number + 1) >=
+              0.7) {
+            useList = true;
+          }
+        }
+      }
+
+      if (useList) {
+        out.println(
+            'static final $coreImportPrefix.List<$classname?> _byValue ='
+            ' $protobufImportPrefix.ProtobufEnum.\$_initDenseList(values);');
+
+        out.println('static $classname? valueOf($coreImportPrefix.int value) =>'
+            '  value < 0 || value >= _byValue.length ? null : _byValue[value];');
+      } else {
+        out.println('static final $coreImportPrefix.List<$classname> _byValue ='
+            ' $protobufImportPrefix.ProtobufEnum.\$_initSparseList(values);');
+
+        out.println('static $classname? valueOf($coreImportPrefix.int value) =>'
+            ' $protobufImportPrefix.ProtobufEnum.\$_binarySearch(_byValue, value);');
+      }
+
       out.println();
 
       out.println('const $classname._(super.v, super.n);');

protoc_plugin/test/goldens/deprecations.pbenum

@@ -24,9 +24,10 @@ class A extends $pb.ProtobufEnum {
     A2,
   ];
 
-  static final $core.Map<$core.int, A> _byValue =
-      $pb.ProtobufEnum.initByValue(values);
-  static A? valueOf($core.int value) => _byValue[value];
+  static final $core.List<A?> _byValue =
+      $pb.ProtobufEnum.$_initDenseList(values);
+  static A? valueOf($core.int value) =>
+      value < 0 || value >= _byValue.length ? null : _byValue[value];
 
   const A._(super.v, super.n);
 }

protoc_plugin/test/goldens/doc_comments.pbenum

@@ -26,9 +26,10 @@ class A extends $pb.ProtobufEnum {
     A2,
   ];
 
-  static final $core.Map<$core.int, A> _byValue =
-      $pb.ProtobufEnum.initByValue(values);
-  static A? valueOf($core.int value) => _byValue[value];
+  static final $core.List<A?> _byValue =
+      $pb.ProtobufEnum.$_initDenseList(values);
+  static A? valueOf($core.int value) =>
+      value < 0 || value >= _byValue.length ? null : _byValue[value];
 
   const A._(super.v, super.n);
 }

protoc_plugin/test/goldens/enum

@@ -11,8 +11,8 @@ class PhoneType extends $pb.ProtobufEnum {
     WORK,
   ];
 
-  static final $core.Map<$core.int, PhoneType> _byValue = $pb.ProtobufEnum.initByValue(values);
-  static PhoneType? valueOf($core.int value) => _byValue[value];
+  static final $core.List<PhoneType?> _byValue = $pb.ProtobufEnum.$_initDenseList(values);
+  static PhoneType? valueOf($core.int value) =>  value < 0 || value >= _byValue.length ? null : _byValue[value];
 
   const PhoneType._(super.v, super.n);
 }

protoc_plugin/test/goldens/messageGeneratorEnums

@@ -11,8 +11,8 @@ class PhoneNumber_PhoneType extends $pb.ProtobufEnum {
     WORK,
   ];
 
-  static final $core.Map<$core.int, PhoneNumber_PhoneType> _byValue = $pb.ProtobufEnum.initByValue(values);
-  static PhoneNumber_PhoneType? valueOf($core.int value) => _byValue[value];
+  static final $core.List<PhoneNumber_PhoneType?> _byValue = $pb.ProtobufEnum.$_initDenseList(values);
+  static PhoneNumber_PhoneType? valueOf($core.int value) =>  value < 0 || value >= _byValue.length ? null : _byValue[value];
 
   const PhoneNumber_PhoneType._(super.v, super.n);
 }

protoc_plugin/test/goldens/topLevelEnum.pbenum

@@ -26,8 +26,8 @@ class PhoneType extends $pb.ProtobufEnum {
     WORK,
   ];
 
-  static final $core.Map<$core.int, PhoneType> _byValue = $pb.ProtobufEnum.initByValue(values);
-  static PhoneType? valueOf($core.int value) => _byValue[value];
+  static final $core.List<PhoneType?> _byValue = $pb.ProtobufEnum.$_initDenseList(values);
+  static PhoneType? valueOf($core.int value) =>  value < 0 || value >= _byValue.length ? null : _byValue[value];
 
   const PhoneType._(super.v, super.n);
 }