Constant evaluation support

editor/tools/plugins/com.google.dart.engine/src/com/google/dart/engine/internal/object/StringState.java

Index: editor/tools/plugins/com.google.dart.engine/src/com/google/dart/engine/internal/object/StringState.java
diff --git a/editor/tools/plugins/com.google.dart.engine/src/com/google/dart/engine/internal/object/StringState.java b/editor/tools/plugins/com.google.dart.engine/src/com/google/dart/engine/internal/object/StringState.java
new file mode 100644
index 0000000000000000000000000000000000000000..6c1c2dbaccc103d0ae0f68cbd29688662f46ff37
--- /dev/null
+++ b/editor/tools/plugins/com.google.dart.engine/src/com/google/dart/engine/internal/object/StringState.java
@@ -0,0 +1,116 @@
+/*
+ * Copyright (c) 2013, the Dart project authors.
+ * 
+ * Licensed under the Eclipse Public License v1.0 (the "License"); you may not use this file except
+ * in compliance with the License. You may obtain a copy of the License at
+ * 
+ * http://www.eclipse.org/legal/epl-v10.html
+ * 
+ * Unless required by applicable law or agreed to in writing, software distributed under the License
+ * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
+ * or implied. See the License for the specific language governing permissions and limitations under
+ * the License.
+ */
+package com.google.dart.engine.internal.object;
+
+import com.google.dart.engine.utilities.general.ObjectUtilities;
+
+/**
+ * Instances of the class {@code StringState} represent the state of an object representing a
+ * string.
+ */
+public class StringState extends InstanceState {
+  /**
+   * The value of this instance.
+   */
+  private String value;
+
+  /**
+   * A state that can be used to represent a double whose value is not known.
+   */
+  public static final StringState UNKNOWN_VALUE = new StringState(null);
+
+  /**
+   * Initialize a newly created state to represent the given value.
+   * 
+   * @param value the value of this instance
+   */
+  public StringState(String value) {
+    this.value = value;
+  }
+
+  @Override
+  public StringState concatenate(InstanceState rightOperand) throws EvaluationException {
+    if (value == null) {
+      return UNKNOWN_VALUE;
+    }
+    if (rightOperand instanceof StringState) {
+      String rightValue = ((StringState) rightOperand).getValue();
+      if (rightValue == null) {
+        return UNKNOWN_VALUE;
+      }
+      return new StringState(value + rightValue);
+    } else if (rightOperand instanceof DynamicState) {
+      return UNKNOWN_VALUE;
+    }
+    return super.concatenate(rightOperand);
+  }
+
+  @Override
+  public StringState convertToString() {
+    return this;
+  }
+
+  @Override
+  public boolean equals(Object object) {
+    return object instanceof StringState
+        && ObjectUtilities.equals(value, ((StringState) object).value);
+  }
+
+  @Override
+  public BoolState equalEqual(InstanceState rightOperand) throws EvaluationException {
+    assertBoolNumStringOrNull(rightOperand);
+    if (value == null) {
+      return BoolState.UNKNOWN_VALUE;
+    }
+    if (rightOperand instanceof StringState) {
+      String rightValue = ((StringState) rightOperand).getValue();
+      if (rightValue == null) {
+        return BoolState.UNKNOWN_VALUE;
+      }
+      return BoolState.from(value.equals(rightValue));
+    } else if (rightOperand instanceof DynamicState) {
+      return BoolState.UNKNOWN_VALUE;
+    }
+    return BoolState.FALSE_STATE;
+  }
+
+  @Override
+  public String getTypeName() {
+    return "String"; //$NON-NLS-0$
+  }
+
+  /**
+   * Return the value of this instance.
+   * 
+   * @return the value of this instance
+   */
+  public String getValue() {
+    return value;
+  }
+
+  @Override
+  public int hashCode() {
+    return value == null ? 0 : value.hashCode();
+  }
+
+  @Override
+  public boolean isBoolNumStringOrNull() {
+    return true;
+  }
+
+  @Override
+  public String toString() {
+    return value == null ? "-unknown-" : "'" + value + "'";
+  }
+}