174 lines
4.2 KiB
Go
Executable File
174 lines
4.2 KiB
Go
Executable File
package refs
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// ElementMapper provides an identity mapping by default.
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//
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// This can be replaced to provide a struct that maps elements to linker
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// objects, if they are not the same. An ElementMapper is not typically
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// required if: Linker is left as is, Element is left as is, or Linker and
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// Element are the same type.
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type weakRefElementMapper struct{}
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// linkerFor maps an Element to a Linker.
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//
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// This default implementation should be inlined.
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//
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//go:nosplit
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func (weakRefElementMapper) linkerFor(elem *WeakRef) *WeakRef { return elem }
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// List is an intrusive list. Entries can be added to or removed from the list
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// in O(1) time and with no additional memory allocations.
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//
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// The zero value for List is an empty list ready to use.
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//
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// To iterate over a list (where l is a List):
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// for e := l.Front(); e != nil; e = e.Next() {
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// // do something with e.
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// }
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//
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// +stateify savable
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type weakRefList struct {
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head *WeakRef
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tail *WeakRef
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}
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// Reset resets list l to the empty state.
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func (l *weakRefList) Reset() {
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l.head = nil
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l.tail = nil
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}
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// Empty returns true iff the list is empty.
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func (l *weakRefList) Empty() bool {
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return l.head == nil
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}
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// Front returns the first element of list l or nil.
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func (l *weakRefList) Front() *WeakRef {
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return l.head
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}
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// Back returns the last element of list l or nil.
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func (l *weakRefList) Back() *WeakRef {
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return l.tail
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}
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// PushFront inserts the element e at the front of list l.
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func (l *weakRefList) PushFront(e *WeakRef) {
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weakRefElementMapper{}.linkerFor(e).SetNext(l.head)
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weakRefElementMapper{}.linkerFor(e).SetPrev(nil)
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if l.head != nil {
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weakRefElementMapper{}.linkerFor(l.head).SetPrev(e)
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} else {
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l.tail = e
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}
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l.head = e
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}
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// PushBack inserts the element e at the back of list l.
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func (l *weakRefList) PushBack(e *WeakRef) {
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weakRefElementMapper{}.linkerFor(e).SetNext(nil)
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weakRefElementMapper{}.linkerFor(e).SetPrev(l.tail)
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if l.tail != nil {
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weakRefElementMapper{}.linkerFor(l.tail).SetNext(e)
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} else {
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l.head = e
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}
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l.tail = e
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}
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// PushBackList inserts list m at the end of list l, emptying m.
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func (l *weakRefList) PushBackList(m *weakRefList) {
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if l.head == nil {
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l.head = m.head
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l.tail = m.tail
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} else if m.head != nil {
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weakRefElementMapper{}.linkerFor(l.tail).SetNext(m.head)
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weakRefElementMapper{}.linkerFor(m.head).SetPrev(l.tail)
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l.tail = m.tail
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}
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m.head = nil
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m.tail = nil
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}
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// InsertAfter inserts e after b.
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func (l *weakRefList) InsertAfter(b, e *WeakRef) {
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a := weakRefElementMapper{}.linkerFor(b).Next()
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weakRefElementMapper{}.linkerFor(e).SetNext(a)
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weakRefElementMapper{}.linkerFor(e).SetPrev(b)
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weakRefElementMapper{}.linkerFor(b).SetNext(e)
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if a != nil {
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weakRefElementMapper{}.linkerFor(a).SetPrev(e)
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} else {
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l.tail = e
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}
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}
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// InsertBefore inserts e before a.
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func (l *weakRefList) InsertBefore(a, e *WeakRef) {
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b := weakRefElementMapper{}.linkerFor(a).Prev()
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weakRefElementMapper{}.linkerFor(e).SetNext(a)
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weakRefElementMapper{}.linkerFor(e).SetPrev(b)
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weakRefElementMapper{}.linkerFor(a).SetPrev(e)
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if b != nil {
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weakRefElementMapper{}.linkerFor(b).SetNext(e)
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} else {
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l.head = e
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}
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}
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// Remove removes e from l.
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func (l *weakRefList) Remove(e *WeakRef) {
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prev := weakRefElementMapper{}.linkerFor(e).Prev()
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next := weakRefElementMapper{}.linkerFor(e).Next()
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if prev != nil {
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weakRefElementMapper{}.linkerFor(prev).SetNext(next)
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} else {
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l.head = next
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}
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if next != nil {
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weakRefElementMapper{}.linkerFor(next).SetPrev(prev)
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} else {
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l.tail = prev
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}
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}
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// Entry is a default implementation of Linker. Users can add anonymous fields
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// of this type to their structs to make them automatically implement the
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// methods needed by List.
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//
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// +stateify savable
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type weakRefEntry struct {
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next *WeakRef
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prev *WeakRef
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}
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// Next returns the entry that follows e in the list.
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func (e *weakRefEntry) Next() *WeakRef {
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return e.next
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}
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// Prev returns the entry that precedes e in the list.
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func (e *weakRefEntry) Prev() *WeakRef {
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return e.prev
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}
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// SetNext assigns 'entry' as the entry that follows e in the list.
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func (e *weakRefEntry) SetNext(elem *WeakRef) {
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e.next = elem
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}
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// SetPrev assigns 'entry' as the entry that precedes e in the list.
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func (e *weakRefEntry) SetPrev(elem *WeakRef) {
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e.prev = elem
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}
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