lib/src/iterables/range.dart

// Copyright 2013 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.

/// Returns an [Iterable] sequence of [num]s.
///
/// If only one argument is provided, [startOrStop] is the upper bound for the
/// sequence. If two or more arguments are provided, [stop] is the upper bound.
///
/// The sequence starts at 0 if one argument is provided, or [startOrStop] if
/// two or more arguments are provided. The sequence increments by 1, or [step]
/// if provided. [step] can be negative, in which case the sequence counts down
/// from the starting point and [stop] must be less than the starting point so
/// that it becomes the lower bound.
Iterable<num> range(num startOrStop, [num? stop, num? step]) sync* {
  final start = stop == null ? 0 : startOrStop;
  stop ??= startOrStop;
  step ??= 1;

  if (step == 0) throw ArgumentError('step cannot be 0');
  if (step > 0 && stop < start) {
    throw ArgumentError('if step is positive, stop must be greater than start');
  }
  if (step < 0 && stop > start) {
    throw ArgumentError('if step is negative, stop must be less than start');
  }

  for (num value = start;
      step < 0 ? value > stop : value < stop;
      value += step) {
    yield value;
  }
}