github.com/mymmsc/gox@v1.3.33/util/doublylinkedlist/iterator.go (about)

     1  // Copyright (c) 2015, Emir Pasic. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package doublylinkedlist
     6  
     7  import (
     8  	"github.com/mymmsc/gox/util"
     9  )
    10  
    11  func assertIteratorImplementation() {
    12  	var _ util.ReverseIteratorWithIndex = (*Iterator)(nil)
    13  }
    14  
    15  // Iterator holding the iterator's state
    16  type Iterator struct {
    17  	list    *List
    18  	index   int
    19  	element *element
    20  }
    21  
    22  // Iterator returns a stateful iterator whose values can be fetched by an index.
    23  func (list *List) Iterator() Iterator {
    24  	return Iterator{list: list, index: -1, element: nil}
    25  }
    26  
    27  // Next moves the iterator to the next element and returns true if there was a next element in the container.
    28  // If Next() returns true, then next element's index and value can be retrieved by Index() and Value().
    29  // If Next() was called for the first time, then it will point the iterator to the first element if it exists.
    30  // Modifies the state of the iterator.
    31  func (iterator *Iterator) Next() bool {
    32  	if iterator.index < iterator.list.size {
    33  		iterator.index++
    34  	}
    35  	if !iterator.list.withinRange(iterator.index) {
    36  		iterator.element = nil
    37  		return false
    38  	}
    39  	if iterator.index != 0 {
    40  		iterator.element = iterator.element.next
    41  	} else {
    42  		iterator.element = iterator.list.first
    43  	}
    44  	return true
    45  }
    46  
    47  // Prev moves the iterator to the previous element and returns true if there was a previous element in the container.
    48  // If Prev() returns true, then previous element's index and value can be retrieved by Index() and Value().
    49  // Modifies the state of the iterator.
    50  func (iterator *Iterator) Prev() bool {
    51  	if iterator.index >= 0 {
    52  		iterator.index--
    53  	}
    54  	if !iterator.list.withinRange(iterator.index) {
    55  		iterator.element = nil
    56  		return false
    57  	}
    58  	if iterator.index == iterator.list.size-1 {
    59  		iterator.element = iterator.list.last
    60  	} else {
    61  		iterator.element = iterator.element.prev
    62  	}
    63  	return iterator.list.withinRange(iterator.index)
    64  }
    65  
    66  // Value returns the current element's value.
    67  // Does not modify the state of the iterator.
    68  func (iterator *Iterator) Value() interface{} {
    69  	return iterator.element.value
    70  }
    71  
    72  // Index returns the current element's index.
    73  // Does not modify the state of the iterator.
    74  func (iterator *Iterator) Index() int {
    75  	return iterator.index
    76  }
    77  
    78  // Begin resets the iterator to its initial state (one-before-first)
    79  // Call Next() to fetch the first element if any.
    80  func (iterator *Iterator) Begin() {
    81  	iterator.index = -1
    82  	iterator.element = nil
    83  }
    84  
    85  // End moves the iterator past the last element (one-past-the-end).
    86  // Call Prev() to fetch the last element if any.
    87  func (iterator *Iterator) End() {
    88  	iterator.index = iterator.list.size
    89  	iterator.element = iterator.list.last
    90  }
    91  
    92  // First moves the iterator to the first element and returns true if there was a first element in the container.
    93  // If First() returns true, then first element's index and value can be retrieved by Index() and Value().
    94  // Modifies the state of the iterator.
    95  func (iterator *Iterator) First() bool {
    96  	iterator.Begin()
    97  	return iterator.Next()
    98  }
    99  
   100  // Last moves the iterator to the last element and returns true if there was a last element in the container.
   101  // If Last() returns true, then last element's index and value can be retrieved by Index() and Value().
   102  // Modifies the state of the iterator.
   103  func (iterator *Iterator) Last() bool {
   104  	iterator.End()
   105  	return iterator.Prev()
   106  }