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quiver/lib/check.dart

-// Copyright 2014 Google Inc. All Rights Reserved.
-//
-// Licensed under the Apache License, Version 2.0 (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.apache.org/licenses/LICENSE-2.0
-//
-// 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.
-
-/// A simple set of pre/post-condition checkers based on the
-/// [Guava](https://code.google.com/p/guava-libraries/) Preconditions
-/// class in Java.
-///
-/// These checks are stronger than 'assert' statements, which can be
-/// switched off, so they must only be used in situations where we actively
-/// want the program to break when the check fails.
-///
-/// ## Performance
-/// Performance may be an issue with these checks if complex logic is computed
-/// in order to make the method call. You should be careful with its use in
-/// these cases - this library is aimed at improving maintainability and
-/// readability rather than performance. They are also useful when the program
-/// should fail early - for example, null-checking a parameter that might not
-/// be used until the end of the method call.
-///
-/// ## Error messages
-/// The message parameter can be either a `() => Object` or any other `Object`.
-/// The object will be converted to an error message by calling its
-/// `toString()`. The `Function` should be preferred if the message is complex
-/// to construct (i.e., it uses `String` interpolation), because it is only
-/// called when the check fails.
-///
-/// If the message parameter is `null` or returns `null`, a default error
-/// message will be used.
-library quiver.check;
-
-/// Throws an [ArgumentError] if the given [expression] is `false`.
-void checkArgument(bool expression, {message}) {
-  if (!expression) {
-    throw new ArgumentError(_resolveMessage(message, null));
-  }
-}
-
-/// Throws a [RangeError] if the given [index] is not a valid index for a list
-/// with [size] elements. Otherwise, returns the [index] parameter.
-int checkListIndex(int index, int size, {message}) {
-  if (index < 0 || index >= size) {
-    throw new RangeError(_resolveMessage(
-        message, 'index $index not valid for list of size $size'));
-  }
-  return index;
-}
-
-/// Throws an [ArgumentError] if the given [reference] is `null`. Otherwise,
-/// returns the [reference] parameter.
-dynamic checkNotNull(reference, {message}) {
-  if (reference == null) {
-    throw new ArgumentError(_resolveMessage(message, 'null pointer'));
-  }
-  return reference;
-}
-
-/// Throws a [StateError] if the given [expression] is `false`.
-void checkState(bool expression, {message}) {
-  if (!expression) {
-    throw new StateError(_resolveMessage(message, 'failed precondition'));
-  }
-}
-
-String _resolveMessage(message, String defaultMessage) {
-  if (message is Function) message = message();
-  if (message == null) return defaultMessage;
-  return message.toString();
-}