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list.go
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list.go
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package orderedmap
// Element is an element of a null terminated (non circular) intrusive doubly linked list that contains the key of the correspondent element in the ordered map too.
type Element 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 *Element
// The key that corresponds to this element in the ordered map.
Key interface{}
// The value stored with this element.
Value interface{}
}
// Next returns the next list element or nil.
func (e *Element) Next() *Element {
return e.next
}
// Prev returns the previous list element or nil.
func (e *Element) Prev() *Element {
return e.prev
}
// list represents a null terminated (non circular) intrusive doubly linked list.
// The list is immediately usable after instantiation without the need of a dedicated initialization.
type list struct {
root Element // list head and tail
}
func (l *list) IsEmpty() bool {
return l.root.next == nil
}
// Front returns the first element of list l or nil if the list is empty.
func (l *list) Front() *Element {
return l.root.next
}
// Back returns the last element of list l or nil if the list is empty.
func (l *list) Back() *Element {
return l.root.prev
}
// Remove removes e from its list
func (l *list) Remove(e *Element) {
if e.prev == nil {
l.root.next = e.next
} else {
e.prev.next = e.next
}
if e.next == nil {
l.root.prev = e.prev
} else {
e.next.prev = e.prev
}
e.next = nil // avoid memory leaks
e.prev = nil // avoid memory leaks
}
// PushFront inserts a new element e with value v at the front of list l and returns e.
func (l *list) PushFront(key interface{}, value interface{}) *Element {
e := &Element{Key: key, Value: value}
if l.root.next == nil {
// It's the first element
l.root.next = e
l.root.prev = e
return e
}
e.next = l.root.next
l.root.next.prev = e
l.root.next = e
return e
}
// PushBack inserts a new element e with value v at the back of list l and returns e.
func (l *list) PushBack(key interface{}, value interface{}) *Element {
e := &Element{Key: key, Value: value}
if l.root.prev == nil {
// It's the first element
l.root.next = e
l.root.prev = e
return e
}
e.prev = l.root.prev
l.root.prev.next = e
l.root.prev = e
return e
}