Tweaks for Iterable.toList() invocations.

pkg/analyzer/lib/src/dart/element/element.dart

Index: pkg/analyzer/lib/src/dart/element/element.dart
diff --git a/pkg/analyzer/lib/src/dart/element/element.dart b/pkg/analyzer/lib/src/dart/element/element.dart
index 1acac44494f2ed5453356df12c96f94bdbab2708..04e7cf260f0ace87522f783343bf6f96e47c3995 100644
--- a/pkg/analyzer/lib/src/dart/element/element.dart
+++ b/pkg/analyzer/lib/src/dart/element/element.dart
@@ -377,7 +377,7 @@ class ClassElementImpl extends ElementImpl
       ResynthesizerContext context = enclosingUnit.resynthesizerContext;
       _interfaces = _unlinkedClass.interfaces
           .map((EntityRef t) => context.resolveTypeRef(t, this))
-          .toList();
+          .toList(growable: false);
     }
     return _interfaces ?? const <InterfaceType>[];
   }
@@ -477,7 +477,7 @@ class ClassElementImpl extends ElementImpl
       ResynthesizerContext context = enclosingUnit.resynthesizerContext;
       _mixins = _unlinkedClass.mixins
           .map((EntityRef t) => context.resolveTypeRef(t, this))
-          .toList();
+          .toList(growable: false);
     }
     return _mixins ?? const <InterfaceType>[];
   }
@@ -884,7 +884,7 @@ class ClassElementImpl extends ElementImpl
       implicitConstructor.enclosingElement = this;
       implicitConstructor.type = new FunctionTypeImpl(implicitConstructor);
       return implicitConstructor;
-    }).toList();
+    }).toList(growable: false);
   }
 
   PropertyAccessorElement _internalLookUpConcreteGetter(
@@ -4607,7 +4607,7 @@ class LibraryElementImpl extends ElementImpl implements LibraryElement {
         libraries.add(library);
       }
     }
-    return new List.from(libraries);
+    return libraries.toList(growable: false);
   }
 
   @override
@@ -4697,7 +4697,7 @@ class LibraryElementImpl extends ElementImpl implements LibraryElement {
         libraries.add(library);
       }
     }
-    return new List.from(libraries);
+    return libraries.toList(growable: false);
   }
 
   @override
@@ -4910,7 +4910,7 @@ class LibraryElementImpl extends ElementImpl implements LibraryElement {
           prefixes.add(prefix);
         }
       }
-      _prefixes = prefixes.toList();
+      _prefixes = prefixes.toList(growable: false);
     }
     return _prefixes;
   }
@@ -4945,9 +4945,9 @@ class LibraryElementImpl extends ElementImpl implements LibraryElement {
 
   @override
   List<LibraryElement> get visibleLibraries {
-    Set<LibraryElement> visibleLibraries = new Set();
+    HashSet<LibraryElement> visibleLibraries = new HashSet<LibraryElement>();

[sra1, 2016/05/31 06:43:56]

Ideally the default implementations would also be most efficient for normal
usage.

Do you have evidence that that this is not the case?
The VM implementation of LinkedHashSet (i.e. Set) is more storage-efficient that
HashSet for more than a 2-3 elements, but I don't know if that translates to
overall performance.

[scheglov, 2016/05/31 15:41:37]

The following performance micro-benchmark uses 67 ms with Set, and 46 ms with
HashSet.
So it seems that HashSet wins.


---------------------
import 'dart:math';
import 'dart:collection';

main() {
  new Benchmark(100, () {
    for (int i = 0; i < 1000000; i++) {
//      HashSet<int> set = new HashSet<int>();
      Set<int> set = new Set<int>();
      set.add(1);
      set.add(2);
      set.toList(growable: false);
    }
  }).run();
}

typedef void BenchmarkIteration();

class Benchmark {
  final int iterationCount;
  final BenchmarkIteration iteration;

  Benchmark(this.iterationCount, this.iteration);

  void run() {
    int best = 1 << 20;
    for (int i = 0; i < iterationCount; i++) {
      Stopwatch sw = new Stopwatch()..start();
      iteration();
      best = min(sw.elapsedMilliseconds, best);
    }
    print('Best time: $best ms.');
  }
}
---------------------

     _addVisibleLibraries(visibleLibraries, false);
-    return new List.from(visibleLibraries);
+    return visibleLibraries.toList(growable: false);
   }
 
   @override
@@ -5790,7 +5790,7 @@ class MultiplyDefinedElementImpl implements MultiplyDefinedElement {
     HashSet<Element> elements = new HashSet<Element>();
     _add(elements, firstElement);
     _add(elements, secondElement);
-    return new List.from(elements);
+    return elements.toList(growable: false);
   }
 }
 
@@ -7326,11 +7326,9 @@ abstract class TypeParameterizedElementMixin
    * element's type parameters.
    */
   List<TypeParameterType> get typeParameterTypes {
-    if (_typeParameterTypes == null) {
-      _typeParameterTypes =
-          typeParameters.map((TypeParameterElement e) => e.type).toList();
-    }
-    return _typeParameterTypes;
+    return _typeParameterTypes ??= typeParameters
+        .map((TypeParameterElement e) => e.type)
+        .toList(growable: false);
   }
 
   /**