Cache values of fields and lists in summary implementations.

pkg/analyzer/lib/src/summary/flat_buffers.dart

 // Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
 // 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.
 
 library analyzer.src.summary.flat_buffers;
 
 import 'dart:collection';
 import 'dart:convert';
 import 'dart:math';
 import 'dart:typed_data';
@@ skipping 483 matching lines @@
     BufferPointer object = ref.derefObject();
     int length = object._getUint32();
     return UTF8
         .decode(ref._buffer.buffer.asUint8List(object._offset + 4, length));
   }
 }
 
 /**
  * An abstract reader for tables.
  */
-abstract class TableReader<T extends TableReader<T>> extends Reader<T> {
+abstract class TableReader<T> extends Reader<T> {
   const TableReader();
 
   @override
   int get size => 4;
 
   /**
-   * Return the [Reader] for reading fields of the object at [bp].
+   * Return the object at [bp].
    */
-  T createReader(BufferPointer bp);
+  T createObject(BufferPointer bp);
 
   @override
   T read(BufferPointer bp) {
     bp = bp.derefObject();
-    return createReader(bp);
+    return createObject(bp);
   }
 }
 
 class _FbList<E> extends Object with ListMixin<E> implements List<E> {
   final Reader<E> elementReader;
   final BufferPointer bp;
+  List<E> cache;
 
   _FbList(this.elementReader, this.bp);
 
   @override
   int get length => bp._getUint32();
 
   @override
   void set length(int i) =>
       throw new StateError('Attempt to modify immutable list');
 
   @override
   E operator [](int i) {
-    BufferPointer ref = bp._advance(4 + elementReader.size * i);
-    return elementReader.read(ref);
+    cache ??= new List<E>(length);
+    E item = cache[i];
+    if (item == null) {
+      BufferPointer ref = bp._advance(4 + elementReader.size * i);
+      item = elementReader.read(ref);
+      cache[i] = item;
+    }
+    return item;
   }
 
   @override
   void operator []=(int i, E e) =>
       throw new StateError('Attempt to modify immutable list');
 }
 
 /**
  * Class that describes the structure of a table.
  */
@@ skipping 61 matching lines @@
     // Table size.
     buf.setUint16(bufOffset, tableSize, Endianness.LITTLE_ENDIAN);
     bufOffset += 2;
     // Field offsets.
     for (int fieldOffset in fieldOffsets) {
       buf.setUint16(bufOffset, fieldOffset, Endianness.LITTLE_ENDIAN);
       bufOffset += 2;
     }
   }
 }