// Copyright (c) 2016, 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. | |

import 'dart:collection'; | |

import 'unmodifiable_wrappers.dart'; | |

/// A single set that provides a view of the union over a set of sets. | |

/// | |

/// Since this is just a view, it reflects all changes in the underlying sets. | |

/// | |

/// If an element is in multiple sets and the outer set is ordered, the version | |

/// in the earliest inner set is preferred. Component sets are assumed to use | |

/// `==` and `hashCode` for equality. | |

class UnionSet<E> extends SetBase<E> with UnmodifiableSetMixin<E> { | |

/// The set of sets that this provides a view of. | |

final Set<Set<E>> _sets; | |

/// Whether the sets in [_sets] are guaranteed to be disjoint. | |

final bool _disjoint; | |

/// Creates a new set that's a view of the union of all sets in [sets]. | |

/// | |

/// If any sets in [sets] change, this [UnionSet] reflects that change. If a | |

/// new set is added to [sets], this [UnionSet] reflects that as well. | |

/// | |

/// If [disjoint] is `true`, then all component sets must be disjoint. That | |

/// is, that they contain no elements in common. This makes many operations | |

/// including [length] more efficient. If the component sets turn out not to | |

/// be disjoint, some operations may behave inconsistently. | |

UnionSet(this._sets, {bool disjoint = false}) : _disjoint = disjoint; | |

/// Creates a new set that's a view of the union of all sets in [sets]. | |

/// | |

/// If any sets in [sets] change, this [UnionSet] reflects that change. | |

/// However, unlike [new UnionSet], this creates a copy of its parameter, so | |

/// changes in [sets] aren't reflected in this [UnionSet]. | |

/// | |

/// If [disjoint] is `true`, then all component sets must be disjoint. That | |

/// is, that they contain no elements in common. This makes many operations | |

/// including [length] more efficient. If the component sets turn out not to | |

/// be disjoint, some operations may behave inconsistently. | |

UnionSet.from(Iterable<Set<E>> sets, {bool disjoint = false}) | |

: this(sets.toSet(), disjoint: disjoint); | |

int get length => _disjoint | |

? _sets.fold(0, (length, set) => length + set.length) | |

: _iterable.length; | |

Iterator<E> get iterator => _iterable.iterator; | |

/// Returns an iterable over the contents of all the sets in [this]. | |

Iterable<E> get _iterable => | |

_disjoint ? _sets.expand((set) => set) : _dedupIterable; | |

/// Returns an iterable over the contents of all the sets in [this] that | |

/// de-duplicates elements. | |

/// | |

/// If the sets aren't guaranteed to be disjoint, this keeps track of the | |

/// elements we've already emitted so that we can de-duplicate them. | |

Iterable<E> get _dedupIterable { | |

var seen = Set<E>(); | |

return _sets.expand((set) => set).where((element) { | |

if (seen.contains(element)) return false; | |

seen.add(element); | |

return true; | |

}); | |

} | |

bool contains(Object element) => _sets.any((set) => set.contains(element)); | |

E lookup(Object element) { | |

if (element == null) return null; | |

return _sets | |

.map((set) => set.lookup(element)) | |

.firstWhere((result) => result != null, orElse: () => null); | |

} | |

Set<E> toSet() { | |

var result = Set<E>(); | |

for (var set in _sets) { | |

result.addAll(set); | |

} | |

return result; | |

} | |

} |