Unify error messages for iterables and lists.

sdk/lib/internal/iterable.dart

 // Copyright (c) 2011, 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.
 
 part of dart._internal;
 
 /**
  * Marker interface for [Iterable] subclasses that have an efficient
  * [length] implementation.
  */
@@ skipping 28 matching lines @@
       action(elementAt(i));
       if (length != this.length) {
         throw new ConcurrentModificationError(this);
       }
     }
   }
 
   bool get isEmpty => length == 0;
 
   E get first {
-    if (length == 0) throw new StateError("No elements");
+    if (length == 0) throw IterableElementError.noElement();
     return elementAt(0);
   }
 
   E get last {
-    if (length == 0) throw new StateError("No elements");
+    if (length == 0) throw IterableElementError.noElement();
     return elementAt(length - 1);
   }
 
   E get single {
-    if (length == 0) throw new StateError("No elements");
-    if (length > 1) throw new StateError("Too many elements");
+    if (length == 0) throw IterableElementError.noElement();
+    if (length > 1) throw IterableElementError.tooMany();
     return elementAt(0);
   }
 
   bool contains(Object element) {
     int length = this.length;
     for (int i = 0; i < length; i++) {
       if (elementAt(i) == element) return true;
       if (length != this.length) {
         throw new ConcurrentModificationError(this);
       }
@@ skipping 26 matching lines @@
   dynamic firstWhere(bool test(E element), { Object orElse() }) {
     int length = this.length;
     for (int i = 0; i < length; i++) {
       E element = elementAt(i);
       if (test(element)) return element;
       if (length != this.length) {
         throw new ConcurrentModificationError(this);
       }
     }
     if (orElse != null) return orElse();
-    throw new StateError("No matching element");
+    throw IterableElementError.noElement();
   }
 
   dynamic lastWhere(bool test(E element), { Object orElse() }) {
     int length = this.length;
     for (int i = length - 1; i >= 0; i--) {
       E element = elementAt(i);
       if (test(element)) return element;
       if (length != this.length) {
         throw new ConcurrentModificationError(this);
       }
     }
     if (orElse != null) return orElse();
-    throw new StateError("No matching element");
+    throw IterableElementError.noElement();
   }
 
   E singleWhere(bool test(E element)) {
     int length = this.length;
     E match = null;
     bool matchFound = false;
     for (int i = 0; i < length; i++) {
       E element = elementAt(i);
       if (test(element)) {
         if (matchFound) {
-          throw new StateError("More than one matching element");
+          throw IterableElementError.tooMany();
         }
         matchFound = true;
         match = element;
       }
       if (length != this.length) {
         throw new ConcurrentModificationError(this);
       }
     }
     if (matchFound) return match;
-    throw new StateError("No matching element");
+    throw IterableElementError.noElement();
   }
 
   String join([String separator = ""]) {
     int length = this.length;
     if (!separator.isEmpty) {
       if (length == 0) return "";
       String first = "${elementAt(0)}";
       if (length != this.length) {
         throw new ConcurrentModificationError(this);
       }
@@ skipping 16 matching lines @@
       }
       return buffer.toString();
     }
   }
 
   Iterable<E> where(bool test(E element)) => super.where(test);
 
   Iterable map(f(E element)) => new MappedListIterable(this, f);
 
   E reduce(E combine(var value, E element)) {
-    if (length == 0) throw new StateError("No elements");
+    if (length == 0) throw IterableElementError.noElement();
     E value = elementAt(0);
     for (int i = 1; i < length; i++) {
       value = combine(value, elementAt(i));
     }
     return value;
   }
 
   fold(var initialValue, combine(var previousValue, E element)) {
     var value = initialValue;
     int length = this.length;
@@ skipping 465 matching lines @@
   const EmptyIterable();
 
   Iterator<E> get iterator => const EmptyIterator();
 
   void forEach(void action(E element)) {}
 
   bool get isEmpty => true;
 
   int get length => 0;
 
-  E get first { throw new StateError("No elements"); }
+  E get first { throw IterableElementError.noElement(); }
 
-  E get last { throw new StateError("No elements"); }
+  E get last { throw IterableElementError.noElement(); }
 
-  E get single { throw new StateError("No elements"); }
+  E get single { throw IterableElementError.noElement(); }
 
   E elementAt(int index) { throw new RangeError.value(index); }
 
   bool contains(Object element) => false;
 
   bool every(bool test(E element)) => true;
 
   bool any(bool test(E element)) => false;
 
   E firstWhere(bool test(E element), { E orElse() }) {
     if (orElse != null) return orElse();
-    throw new StateError("No matching element");
+    throw IterableElementError.noElement();
   }
 
   E lastWhere(bool test(E element), { E orElse() }) {
     if (orElse != null) return orElse();
-    throw new StateError("No matching element");
+    throw IterableElementError.noElement();
   }
 
   E singleWhere(bool test(E element), { E orElse() }) {
     if (orElse != null) return orElse();
-    throw new StateError("No matching element");
+    throw IterableElementError.noElement();
   }
 
   String join([String separator = ""]) => "";
 
   Iterable<E> where(bool test(E element)) => this;
 
   Iterable map(f(E element)) => const EmptyIterable();
 
   E reduce(E combine(E value, E element)) {
-    throw new StateError("No elements");
+    throw IterableElementError.noElement();
   }
 
   fold(var initialValue, combine(var previousValue, E element)) {
     return initialValue;
   }
 
   Iterable<E> skip(int count) {
     if (count < 0) throw new RangeError.value(count);
     return this;
   }
@@ skipping 56 matching lines @@
   static bool every(Iterable iterable, bool f(o)) {
     for (final e in iterable) {
       if (!f(e)) return false;
     }
     return true;
   }
 
   static dynamic reduce(Iterable iterable,
                         dynamic combine(previousValue, element)) {
     Iterator iterator = iterable.iterator;
-    if (!iterator.moveNext()) throw new StateError("No elements");
+    if (!iterator.moveNext()) throw IterableElementError.noElement();
     var value = iterator.current;
     while (iterator.moveNext()) {
       value = combine(value, iterator.current);
     }
     return value;
   }
 
   static dynamic fold(Iterable iterable,
                       dynamic initialValue,
                       dynamic combine(dynamic previousValue, element)) {
@@ skipping 29 matching lines @@
     }
   }
 
   static bool isEmpty(Iterable iterable) {
     return !iterable.iterator.moveNext();
   }
 
   static dynamic first(Iterable iterable) {
     Iterator it = iterable.iterator;
     if (!it.moveNext()) {
-      throw new StateError("No elements");
+      throw IterableElementError.noElement();
     }
     return it.current;
   }
 
   static dynamic last(Iterable iterable) {
     Iterator it = iterable.iterator;
     if (!it.moveNext()) {
-      throw new StateError("No elements");
+      throw IterableElementError.noElement();
     }
     dynamic result;
     do {
       result = it.current;
     } while(it.moveNext());
     return result;
   }
 
   static dynamic single(Iterable iterable) {
     Iterator it = iterable.iterator;
-    if (!it.moveNext()) throw new StateError("No elements");
+    if (!it.moveNext()) throw IterableElementError.noElement();
     dynamic result = it.current;
-    if (it.moveNext()) throw new StateError("More than one element");
+    if (it.moveNext()) throw IterableElementError.tooMany();
     return result;
   }
 
   static dynamic firstWhere(Iterable iterable,
                             bool test(dynamic value),
                             dynamic orElse()) {
     for (dynamic element in iterable) {
       if (test(element)) return element;
     }
     if (orElse != null) return orElse();
-    throw new StateError("No matching element");
+    throw IterableElementError.noElement();
   }
 
   static dynamic lastWhere(Iterable iterable,
                            bool test(dynamic value),
                            dynamic orElse()) {
     dynamic result = null;
     bool foundMatching = false;
     for (dynamic element in iterable) {
       if (test(element)) {
         result = element;
         foundMatching = true;
       }
     }
     if (foundMatching) return result;
     if (orElse != null) return orElse();
-    throw new StateError("No matching element");
+    throw IterableElementError.noElement();
   }
 
   static dynamic lastWhereList(List list,
                                bool test(dynamic value),
                                dynamic orElse()) {
     // TODO(floitsch): check that arguments are of correct type?
     for (int i = list.length - 1; i >= 0; i--) {
       dynamic element = list[i];
       if (test(element)) return element;
     }
     if (orElse != null) return orElse();
-    throw new StateError("No matching element");
+    throw IterableElementError.noElement();
   }
 
   static dynamic singleWhere(Iterable iterable, bool test(dynamic value)) {
     dynamic result = null;
     bool foundMatching = false;
     for (dynamic element in iterable) {
       if (test(element)) {
         if (foundMatching) {
-          throw new StateError("More than one matching element");
+          throw IterableElementError.tooMany();
         }
         result = element;
         foundMatching = true;
       }
     }
     if (foundMatching) return result;
-    throw new StateError("No matching element");
+    throw IterableElementError.noElement();
   }
 
   static dynamic elementAt(Iterable iterable, int index) {
     if (index is! int || index < 0) throw new RangeError.value(index);
     int remaining = index;
     for (dynamic element in iterable) {
       if (remaining == 0) return element;
       remaining--;
     }
     throw new RangeError.value(index);
@@ skipping 137 matching lines @@
     List otherList;
     int otherStart;
     if (from is List) {
       otherList = from;
       otherStart = skipCount;
     } else {
       otherList = from.skip(skipCount).toList(growable: false);
       otherStart = 0;
     }
     if (otherStart + length > otherList.length) {
-      throw new StateError("Not enough elements");
+      throw IterableElementError.tooFew();
     }
     Lists.copy(otherList, otherStart, list, start, length);
   }
 
   static void replaceRangeList(List list, int start, int end,
                                Iterable iterable) {
     _rangeCheck(list, start, end);
     if (iterable is! EfficientLength) {
       iterable = iterable.toList();
     }
@@ skipping 86 matching lines @@
 
   static Set setDifference(Set set, Set other, Set result) {
     for (var element in set) {
       if (!other.contains(element)) {
         result.add(element);
       }
     }
     return result;
   }
 }
+
+/**
+ * Creates errors throw by [Iterable] when the element count is wrong.
+ */
+abstract class IterableElementError {
+  /** Error thrown thrown by, e.g., [Iterable.first] when there is no result. */
+  static StateError noElement() => new StateError("No element");
+  /** Error thrown by, e.g., [Iterable.single] if there are too many results. */
+  static StateError tooMany() => new StateError("Too many elements");
+  /** Error thrown by, e.g., [List.setRange] if there are too few elements. */
+  static StateError tooFew() => new StateError("Too few elements");
+}