Operators.

frog/tests/leg_only/src/CompoundOperatorIndexTest.dart

+// Copyright (c) 2012, 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.
+
+class A {
+  List<int> list;
+  A(int a, int b) : list = <int>[a, b];
+  operator [](index) => list[index];
+  operator []=(index, value) => list[index] = value;
+}
+
+main() {
+  A a = new A(1, 2);
+  Expect.equals(1, a[0]);
+  Expect.equals(2, a[1]);
+
+  Expect.equals(1, a[0]++);
+  Expect.equals(2, a[0]);
+
+  Expect.equals(2, a[0]--);
+  Expect.equals(1, a[0]);
+
+  Expect.equals(0, --a[0]);
+  Expect.equals(0, a[0]);
+
+  Expect.equals(1, ++a[0]);
+  Expect.equals(1, a[0]);
+
+  a[0] += 2;

[Lasse Reichstein Nielsen, 2012/01/27 09:42:34]

Try testing that the object and operand are only evaluated once, and that we
only call the [] and []= operators once each, and in the correct order.

Something like:

List<int> trace = <int>[];
class B {
  int value = 100;
  operator [](index) { 
    trace.add(-3); 
    trace.add(index); 
    trace.add(this.value);
    this.value = this.value + 1; 
    return this; 
  }
  operator []=(index, value) { 
    trace.add(-5);
    trace.add(index);
    trace.add(value.value);
    this.value = this.value + 1;
  }
  operator +(int value) {
    trace.add(-4);
    trace.add(this.value);
    trace.add(value);
    this.value = this.value + 1;
    return this;
  }
}

var b = new B();
B getB() {
  trace.add(-1);
  return new B();
}
int getIndex() {
  trace.add(-2);
  return 42;
}
getB()[getIndex()] += 37;

and then check that trace is 
 [-1, -2, -3, 42, 100, -4, 101, 37, -5, 42, 102]

[ngeoffray, 2012/01/27 10:50:04]

Done, with some little tweaks :)

+  Expect.equals(3, a[0]);
+}