gods/lists/singlylinkedlist/iterator.go

/*
Copyright (c) 2015, Emir Pasic
All rights reserved.

Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are met:

* Redistributions of source code must retain the above copyright notice, this
  list of conditions and the following disclaimer.

* Redistributions in binary form must reproduce the above copyright notice,
  this list of conditions and the following disclaimer in the documentation
  and/or other materials provided with the distribution.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/

package singlylinkedlist

import "github.com/emirpasic/gods/containers"

func assertIteratorImplementation() {
	var _ containers.IteratorWithIndex = (*Iterator)(nil)
}

// Iterator holding the iterator's state
type Iterator struct {
	list    *List
	index   int
	element *element
}

// Iterator returns a stateful iterator whose values can be fetched by an index.
func (list *List) Iterator() Iterator {
	return Iterator{list: list, index: -1, element: nil}
}

// Next moves the iterator to the next element and returns true if there was a next element in the container.
// If Next() returns true, then next element's index and value can be retrieved by Index() and Value().
// If Next() was called for the first time, then it will point the iterator to the first element if it exists.
// Modifies the state of the iterator.
func (iterator *Iterator) Next() bool {
	if iterator.index < iterator.list.size {
		iterator.index++
	}
	if !iterator.list.withinRange(iterator.index) {
		iterator.element = nil
		return false
	}
	if iterator.index == 0 {
		iterator.element = iterator.list.first
	} else {
		iterator.element = iterator.element.next
	}
	return true
}

// Value returns the current element's value.
// Does not modify the state of the iterator.
func (iterator *Iterator) Value() interface{} {
	return iterator.element.value
}

// Index returns the current element's index.
// Does not modify the state of the iterator.
func (iterator *Iterator) Index() int {
	return iterator.index
}

// Begin resets the iterator to its initial state (one-before-first)
// Call Next() to fetch the first element if any.
func (iterator *Iterator) Begin() {
	iterator.index = -1
	iterator.element = nil
}

// First moves the iterator to the first element and returns true if there was a first element in the container.
// If First() returns true, then first element's index and value can be retrieved by Index() and Value().
// Modifies the state of the iterator.
func (iterator *Iterator) First() bool {
	iterator.Begin()
	return iterator.Next()
}