gotemplate_StudentList.go

// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
//
// Modified into a gotemplate by Nick Craig-Wood <nick@craig-wood.com>

// Package list implements a doubly linked list.
//
// To iterate over a list (where l is a *List):
//	for e := l.Front(); e != nil; e = e.Next() {
//		// do something with e.Value
//	}
//
package education

// template type List(A)

// ListElement is an element of a linked list.
type StudentListElement struct {
	// Next and previous pointers in the doubly-linked list of elements.
	// To simplify the implementation, internally a list l is implemented
	// as a ring, such that &l.root is both the next element of the last
	// list element (l.Back()) and the previous element of the first list
	// element (l.Front()).
	next, prev *StudentListElement

	// The list to which this element belongs.
	list *StudentList

	// The value stored with this element.
	Value Student
}

// Next returns the next list element or nil.
func (e *StudentListElement) Next() *StudentListElement {
	if p := e.next; p != &e.list.root {
		return p
	}
	return nil
}

// Prev returns the previous list element or nil.
func (e *StudentListElement) Prev() *StudentListElement {
	if p := e.prev; p != &e.list.root {
		return p
	}
	return nil
}

// List represents a doubly linked list.
// The zero value for List is an empty list ready to use.
type StudentList struct {
	root StudentListElement // sentinel list element, only &root, root.prev, and root.next are used
	len  int                // current list length excluding (this) sentinel element
}

// Init initializes or clears list l.
func (l *StudentList) Init() *StudentList {
	l.root.next = &l.root
	l.root.prev = &l.root
	l.len = 0
	return l
}

// New returns an initialized list.
func NewStudentList() *StudentList { return new(StudentList).Init() }

// Len returns the number of elements of list l.
func (l *StudentList) Len() int { return l.len }

// Front returns the first element of list l or nil
func (l *StudentList) Front() *StudentListElement {
	if l.len == 0 {
		return nil
	}
	return l.root.next
}

// Back returns the last element of list l or nil.
func (l *StudentList) Back() *StudentListElement {
	if l.len == 0 {
		return nil
	}
	return l.root.prev
}

// lazyInit lazily initializes a zero List value.
func (l *StudentList) lazyInit() {
	if l.root.next == nil {
		l.Init()
	}
}

// insert inserts e after at, increments l.len, and returns e.
func (l *StudentList) insert(e, at *StudentListElement) *StudentListElement {
	n := at.next
	at.next = e
	e.prev = at
	e.next = n
	n.prev = e
	e.list = l
	l.len++
	return e
}

// insertValue is a convenience wrapper for insert(&ListElement{Value: v}, at).
func (l *StudentList) insertValue(v Student, at *StudentListElement) *StudentListElement {
	return l.insert(&StudentListElement{Value: v}, at)
}

// remove removes e from its list, decrements l.len, and returns e.
func (l *StudentList) remove(e *StudentListElement) *StudentListElement {
	e.prev.next = e.next
	e.next.prev = e.prev
	e.next = nil // avoid memory leaks
	e.prev = nil // avoid memory leaks
	e.list = nil
	l.len--
	return e
}

// Remove removes e from l if e is an element of list l.
// It returns the element value e.Value.
func (l *StudentList) Remove(e *StudentListElement) Student {
	if e.list == l {
		// if e.list == l, l must have been initialized when e was inserted
		// in l or l == nil (e is a zero ListElement) and l.remove will crash
		l.remove(e)
	}
	return e.Value
}

// Pushfront inserts a new element e with value v at the front of list l and returns e.
func (l *StudentList) PushFront(v Student) *StudentListElement {
	l.lazyInit()
	return l.insertValue(v, &l.root)
}

// PushBack inserts a new element e with value v at the back of list l and returns e.
func (l *StudentList) PushBack(v Student) *StudentListElement {
	l.lazyInit()
	return l.insertValue(v, l.root.prev)
}

// InsertBefore inserts a new element e with value v immediately before mark and returns e.
// If mark is not an element of l, the list is not modified.
func (l *StudentList) InsertBefore(v Student, mark *StudentListElement) *StudentListElement {
	if mark.list != l {
		return nil
	}
	// see comment in List.Remove about initialization of l
	return l.insertValue(v, mark.prev)
}

// InsertAfter inserts a new element e with value v immediately after mark and returns e.
// If mark is not an element of l, the list is not modified.
func (l *StudentList) InsertAfter(v Student, mark *StudentListElement) *StudentListElement {
	if mark.list != l {
		return nil
	}
	// see comment in List.Remove about initialization of l
	return l.insertValue(v, mark)
}

// MoveToFront moves element e to the front of list l.
// If e is not an element of l, the list is not modified.
func (l *StudentList) MoveToFront(e *StudentListElement) {
	if e.list != l || l.root.next == e {
		return
	}
	// see comment in List.Remove about initialization of l
	l.insert(l.remove(e), &l.root)
}

// MoveToBack moves element e to the back of list l.
// If e is not an element of l, the list is not modified.
func (l *StudentList) MoveToBack(e *StudentListElement) {
	if e.list != l || l.root.prev == e {
		return
	}
	// see comment in List.Remove about initialization of l
	l.insert(l.remove(e), l.root.prev)
}

// PushBackList inserts a copy of an other list at the back of list l.
// The lists l and other may be the same.
func (l *StudentList) PushBackList(other *StudentList) {
	l.lazyInit()
	for i, e := other.Len(), other.Front(); i > 0; i, e = i-1, e.Next() {
		l.insertValue(e.Value, l.root.prev)
	}
}

// PushFrontList inserts a copy of an other list at the front of list l.
// The lists l and other may be the same.
func (l *StudentList) PushFrontList(other *StudentList) {
	l.lazyInit()
	for i, e := other.Len(), other.Back(); i > 0; i, e = i-1, e.Prev() {
		l.insertValue(e.Value, &l.root)
	}
}