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container/list: fix Remove bug and use pointer to self as identifier

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Remove wasn't nil'ing the *Element.id. This property was exploited
by MoveToFront and MoveToBack internally, so I renamed the existing
Remove to "remove", and created an exported wrapper "Remove" that does
the right thing for the user's sake.

Also, saved an allocation by using *List as the id rather than *byte.

Fixes #1224.

R=rsc, dsymonds
CC=golang-dev
https://golang.org/cl/2685042
This commit is contained in:
Andrew Gerrand 2010-10-25 14:37:30 +11:00
parent ee065332dd
commit 01389b966e
2 changed files with 38 additions and 19 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

40
src/pkg/container/list/list.go
View File

@ -11,8 +11,8 @@ type Element struct {
// The front of the list has prev = nil, and the back has next = nil.
next, prev *Element
// A unique ID for the list to which this element belongs.
id *byte
// Thie list to which this element belongs.
list *List
// The contents of this list element.
Value interface{}
@ -29,7 +29,6 @@ func (e *Element) Prev() *Element { return e.prev }
type List struct {
front, back *Element
len int
id *byte
}
// Init initializes or clears a List.
@ -37,7 +36,6 @@ func (l *List) Init() *List {
l.front = nil
l.back = nil
l.len = 0
l.id = new(byte)
return l
}
@ -52,7 +50,15 @@ func (l *List) Back() *Element { return l.back }
// Remove removes the element from the list.
func (l *List) Remove(e *Element) {
if e.id != l.id {
l.remove(e)
e.list = nil // do what remove does not
}
// remove the element from the list, but do not clear the Element's list field.
// This is so that other List methods may use remove when relocating Elements
// without needing to restore the list field.
func (l *List) remove(e *Element) {
if e.list != l {
return
}
if e.prev == nil {
@ -121,59 +127,59 @@ func (l *List) insertBack(e *Element) {
// PushFront inserts the value at the front of the list and returns a new Element containing the value.
func (l *List) PushFront(value interface{}) *Element {
if l.id == nil {
if l == nil {
l.Init()
}
e := &Element{nil, nil, l.id, value}
e := &Element{nil, nil, l, value}
l.insertFront(e)
return e
}
// PushBack inserts the value at the back of the list and returns a new Element containing the value.
func (l *List) PushBack(value interface{}) *Element {
if l.id == nil {
if l == nil {
l.Init()
}
e := &Element{nil, nil, l.id, value}
e := &Element{nil, nil, l, value}
l.insertBack(e)
return e
}
// InsertBefore inserts the value immediately before mark and returns a new Element containing the value.
func (l *List) InsertBefore(value interface{}, mark *Element) *Element {
if mark.id != l.id {
if mark.list != l {
return nil
}
e := &Element{nil, nil, l.id, value}
e := &Element{nil, nil, l, value}
l.insertBefore(e, mark)
return e
}
// InsertAfter inserts the value immediately after mark and returns a new Element containing the value.
func (l *List) InsertAfter(value interface{}, mark *Element) *Element {
if mark.id != l.id {
if mark.list != l {
return nil
}
e := &Element{nil, nil, l.id, value}
e := &Element{nil, nil, l, value}
l.insertAfter(e, mark)
return e
}
// MoveToFront moves the element to the front of the list.
func (l *List) MoveToFront(e *Element) {
if e.id != l.id || l.front == e {
if e.list != l || l.front == e {
return
}
l.Remove(e)
l.remove(e)
l.insertFront(e)
}
// MoveToBack moves the element to the back of the list.
func (l *List) MoveToBack(e *Element) {
if e.id != l.id || l.back == e {
if e.list != l || l.back == e {
return
}
l.Remove(e)
l.remove(e)
l.insertBack(e)
}

17
src/pkg/container/list/list_test.go
View File

@ -23,8 +23,7 @@ func checkListPointers(t *testing.T, l *List, es []*Element) {
t.Errorf("l.back = %v, want %v", l.back, last)
}
for i := 0; i < len(es); i++ {
e := es[i]
for i, e := range es {
var e_prev, e_next *Element = nil, nil
if i > 0 {
e_prev = es[i-1]
@ -194,3 +193,17 @@ func TestExtending(t *testing.T) {
l1.PushFrontList(l3)
checkList(t, l1, []interface{}{1, 2, 3})
}
func TestRemove(t *testing.T) {
l := New()
e1 := l.PushBack(1)
e2 := l.PushBack(2)
checkListPointers(t, l, []*Element{e1, e2})
e := l.Front()
l.Remove(e)
checkListPointers(t, l, []*Element{e2})
checkListLen(t, l, 1)
l.Remove(e)
checkListPointers(t, l, []*Element{e2})
checkListLen(t, l, 1)
}