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