github.com/mymmsc/gox@v1.3.33/util/arraystack/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 arraystack
     6  
     7  import (
     8  	"github.com/mymmsc/gox/util"
     9  )
    10  
    11  func assertIteratorImplementation() {
    12  	var _ util.ReverseIteratorWithIndex = (*Iterator)(nil)
    13  }
    14  
    15  // Iterator returns a stateful iterator whose values can be fetched by an index.
    16  type Iterator struct {
    17  	stack *Stack
    18  	index int
    19  }
    20  
    21  // Iterator returns a stateful iterator whose values can be fetched by an index.
    22  func (stack *Stack) Iterator() Iterator {
    23  	return Iterator{stack: stack, index: -1}
    24  }
    25  
    26  // Next moves the iterator to the next element and returns true if there was a next element in the container.
    27  // If Next() returns true, then next element's index and value can be retrieved by Index() and Value().
    28  // If Next() was called for the first time, then it will point the iterator to the first element if it exists.
    29  // Modifies the state of the iterator.
    30  func (iterator *Iterator) Next() bool {
    31  	if iterator.index < iterator.stack.Size() {
    32  		iterator.index++
    33  	}
    34  	return iterator.stack.withinRange(iterator.index)
    35  }
    36  
    37  // Prev moves the iterator to the previous element and returns true if there was a previous element in the container.
    38  // If Prev() returns true, then previous element's index and value can be retrieved by Index() and Value().
    39  // Modifies the state of the iterator.
    40  func (iterator *Iterator) Prev() bool {
    41  	if iterator.index >= 0 {
    42  		iterator.index--
    43  	}
    44  	return iterator.stack.withinRange(iterator.index)
    45  }
    46  
    47  // Value returns the current element's value.
    48  // Does not modify the state of the iterator.
    49  func (iterator *Iterator) Value() interface{} {
    50  	value, _ := iterator.stack.list.Get(iterator.stack.list.Size() - iterator.index - 1) // in reverse (LIFO)
    51  	return value
    52  }
    53  
    54  // Index returns the current element's index.
    55  // Does not modify the state of the iterator.
    56  func (iterator *Iterator) Index() int {
    57  	return iterator.index
    58  }
    59  
    60  // Begin resets the iterator to its initial state (one-before-first)
    61  // Call Next() to fetch the first element if any.
    62  func (iterator *Iterator) Begin() {
    63  	iterator.index = -1
    64  }
    65  
    66  // End moves the iterator past the last element (one-past-the-end).
    67  // Call Prev() to fetch the last element if any.
    68  func (iterator *Iterator) End() {
    69  	iterator.index = iterator.stack.Size()
    70  }
    71  
    72  // First moves the iterator to the first element and returns true if there was a first element in the container.
    73  // If First() returns true, then first element's index and value can be retrieved by Index() and Value().
    74  // Modifies the state of the iterator.
    75  func (iterator *Iterator) First() bool {
    76  	iterator.Begin()
    77  	return iterator.Next()
    78  }
    79  
    80  // Last moves the iterator to the last element and returns true if there was a last element in the container.
    81  // If Last() returns true, then last element's index and value can be retrieved by Index() and Value().
    82  // Modifies the state of the iterator.
    83  func (iterator *Iterator) Last() bool {
    84  	iterator.End()
    85  	return iterator.Prev()
    86  }