Doubly-linked list/Element definition: Difference between revisions

=={{header|Action!}}==

TYPE ListNode=[

BYTE data

{{out}}

[https://gitlab.com/amarok8bit/action-rosetta-code/-/raw/master/images/Doubly-linked_list_element_definition.png Screenshot from Atari 8-bit computer]

=={{header|Ada}}==

type Link_Access is access Link;

type Link is record

Prev : Link_Access := null;

Data : Integer;

Using generics, the specification might look like this:

type Element_Type is private;

package Linked_List is

Traversing : Boolean := False; -- True when in a traversal.

end record;

In Ada 2005 this example can be written without declaration of an access type:

Next : not null access Link := Link'Unchecked_Access;

Prev : not null access Link := Link'Unchecked_Access;

Data : Integer;

Here the list element is created already pointing to itself, so that no further initialization is required. The type of the element is marked as ''limited'' indicating that such elements have referential semantics and cannot be copied.

{{works with|ALGOL 68G|Any - tested with release [http://sourceforge.net/projects/algol68/files/algol68g/algol68g-2.7 algol68g-2.7].}}

{{works with|ELLA ALGOL 68|Any (with appropriate job cards) - tested with release [http://sourceforge.net/projects/algol68/files/algol68toc/algol68toc-1.8.8d/algol68toc-1.8-8d.fc9.i386.rpm/download 1.8-8d]}}

CO REQUIRES:

MODE OBJVALUE = ~ # Mode/type of actual obj to be queued #

PROC obj link free = (REF OBJLINK free)VOID:

=={{header|ALGOL W}}==

record DListIElement ( reference(DListIElement) prev

; integer iValue

; reference(DListIElement) next

);

=={{header|ARM Assembly}}==

{{works with|as|Raspberry Pi}}

/* ARM assembly Raspberry PI */

.struct NDlist_value + 4

NDlist_fin:

=={{header|AutoHotkey}}==

=={{header|Axe}}==

r₂→{r₁}ʳ

0→{r₁+2}ʳ

Lbl VALUE

{r₁}ʳ

=={{header|BBC BASIC}}==

{{works with|BBC BASIC for Windows}}

=={{header|Bracmat}}==

=={{header|C}}==

It basically doesn't matter if we use the name link, node, Node or some other name. These are matters of taste and aesthetics. However, it is important that the C language is case-sensitive and that the namespace for structures is separate.

{

struct Node *next;

struct Node *prev;

void *data;

An alternative technique is to define a pointer type by typedef as shown below. The advantage here is that you do not have to write struct everywhere - assuming that you will most often need a pointer to a struct Node, not the structure itself.

struct Node;

typedef struct Node* Node;

void* data;

};

=={{header|C sharp|C#}}==

{

public int Item { get; set; }

Next = next;

}

=={{header|C++}}==

C++ has doubly linked list class template in standard library. However actual list noded are treated as implementation detail and encapsulated inside list. If we were to reimplement list, then node could look like that:

struct Node

{

Node* prev;

T data;

=={{header|Clojure}}==

This sort of mutable structure is not idiomatic in Clojure. [[../Definition#Clojure]] or a finger tree implementation would be better.

(defn new-node [prev next data]

=={{header|Common Lisp}}==

See the functions on the [[Doubly-Linked List]] page for the usage of these structures.

=={{header|D}}==

A default constructor is implicit:

T data;

typeof(this)* prev, next;

alias N = Node!int;

N* n = new N(10);

=={{header|Delphi}}==

type

end;

=={{header|E}}==

This does no type-checking, under the assumption that it is being used by a containing doubly-linked list object which enforces that invariant along with others such as that <code>element.getNext().getPrev() == element</code>. See [[Doubly-Linked List#E]] for an actual implementation (which uses slightly more elaborate nodes than this).

def element {

to setValue(v) { value := v }

return element

=={{header|Erlang}}==

Using the code in [[Doubly-linked_list/Definition]] the element is defined by:

new( Data ) -> erlang:spawn( fun() -> loop( Data, noprevious, nonext ) end ).

=={{header|F_Sharp|F#}}==

type 'a DLElm = {

mutable prev: 'a DLElm option

mutable next: 'a DLElm option

}

=={{header|Factor}}==

=={{header|Fortran}}==

In ISO Fortran 95 or later:

real :: data

type(node), pointer :: next => null(), previous => null()

! . . . .

!

=={{header|FreeBASIC}}==

nxt as node ptr

prv as node ptr

dat as any ptr 'points to any kind of data; user's responsibility

'to keep track of what's actually in it

=={{header|Go}}==

string

next, prev *dlNode

Or, using the [http://golang.org/pkg/container/list/#Element container/list] package:

var node list.Element

=={{header|Haskell}}==

Note that unlike naive pointer manipulation which could corrupt the doubly-linked list, updateLeft and updateRight will always yield a well-formed data structure.

data DList a = Leaf | Node (DList a) a (DList a)

where current = Node l v next

next = updateRight nr new

==Icon and {{header|Unicon}}==

Uses Unicon classes.

class DoubleLink (value, prev_link, next_link)

initially (value, prev_link, next_link)

self.next_link := next_link

end

=={{header|J}}==

Nevertheless, this is doable, though it necessarily departs from the definition specified at [[Doubly-linked_list/Definition#J]].

create=:3 :0

this=:coname''

'predecessor successor data'=:y

successor__predecessor=: predecessor__successor=: this

Here, when we create a new list element, we need to specify its successor node and its predecessor node and the data to be stored in the node. To start a new list we will need a node that can be the head and the tail of the list -- this will be the successor node for the last element of the list and the predecessor node for the first element of the list:

create=:3 :0

predecessor=:successor=:this=: coname''

=={{header|Java}}==

{{works with|Java|1.5+}}

private T element;

private Node<T> next, prev;

return prev;

}

For use with [[Java]] 1.4 and below, delete all "<T>"s and replace T's with "Object".

=={{header|JavaScript}}==

Inherits from LinkedList (see [[Singly-Linked_List_(element)#JavaScript]])

this._value = value;

this._next = next;

}

=={{header|Julia}}==

{{works with|Julia|0.6}}

struct EmptyNode{T} <: AbstractNode{T} end

pred::AbstractNode{T}

succ::AbstractNode{T}

=={{header|Kotlin}}==

class Node<T: Number>(var data: T, var prev: Node<T>? = null, var next: Node<T>? = null) {

println(n2)

println(n3)

{{out}}

=={{header|Lua}}==

see [[Doubly-linked_list/Definition#Lua]], essentially:

=={{header|Mathematica}}/{{header|Wolfram Language}}==

Mathematica and the Wolfram Language have no lower-level way of handling pointers. It does have a built-in, compilable doubly-linked list data structure:

=={{header|Modula-2}}==

Link = POINTER TO LinkRcd;

LinkRcd = RECORD

Prev, Next: Link;

Data: INTEGER

=={{header|Nim}}==

Node[T] = ref TNode[T]

TNode[T] = object

next, prev: Node[T]

=={{header|Oberon-2}}==

MODULE Box;

TYPE

(* ... *)

END Collections.

=={{header|Objeck}}==

@value : Base;

@next : ListNode;

return @previous;

}

=={{header|OCaml}}==

===Imperative===

mutable data: 'a;

mutable next: 'a dlink option;

in

aux

iter_forward_dlink (Printf.printf "%d\n") dl ;;

1

4

5

===Functional===

examples of this page and its task, but in regular OCaml these kind of imperative structures can be advantageously replaced by a functional equivalent, that can be use in the same area, which is to have a list of elements and be able to point to one of these. We can use this type:

The middle element is the pointed item, and the two lists are the

previous and the following items.

Here are the associated functions:

| hd::tl -> [], hd, tl

| [] -> invalid_arg "empty list"

prev_tl, prev, item::next

| _ ->

val nl : 'a list * int * int list = ([], 1, [2; 3; 4; 5])

# let nl = next nl ;;

# current nl ;;

=={{header|Oforth}}==

Complete definition is here : [[../Definition#Oforth]]

=={{header|Oz}}==

We show how to create a new node as a record value.

node(prev:{NewCell _}

next:{NewCell _}

value:Value)

Note: this is for illustrative purposes only. In a real Oz program, you would use one of the existing data types.

=={{header|Pascal}}==

data_ptr = ^data; (* presumes that type 'data' is defined above *)

link = record

next: link_ptr;

data: data_ptr;

=={{header|Perl}}==

data => 'say what',

next => \%foo_node,

prev => \%bar_node,

);

=={{header|Phix}}==

In Phix, types are used for validation and debugging rather than specification purposes. For extensive run-time checking you could use

<span style="color: #008080;">enum</span> <span style="color: #000000;">NEXT</span><span style="color: #0000FF;">,</span><span style="color: #000000;">PREV</span><span style="color: #0000FF;">,</span><span style="color: #000000;">DATA</span>

<span style="color: #008080;">type</span> <span style="color: #000000;">slnode</span><span style="color: #0000FF;">(</span><span style="color: #004080;">object</span> <span style="color: #000000;">x</span><span style="color: #0000FF;">)</span>

<span style="color: #008080;">return</span> <span style="color: #0000FF;">(</span><span style="color: #004080;">sequence</span><span style="color: #0000FF;">(</span><span style="color: #000000;">x</span><span style="color: #0000FF;">)</span> <span style="color: #008080;">and</span> <span style="color: #7060A8;">length</span><span style="color: #0000FF;">(</span><span style="color: #000000;">x</span><span style="color: #0000FF;">)=</span><span style="color: #000000;">DATA</span> <span style="color: #008080;">and</span> <span style="color: #0000FF;"><</span><span style="color: #000000;">i</span><span style="color: #0000FF;">></span><span style="color: #000000;">udt</span><span style="color: #0000FF;"></</span><span style="color: #000000;">i</span><span style="color: #0000FF;">>(</span><span style="color: #000000;">x</span><span style="color: #0000FF;">[</span><span style="color: #000000;">DATA</span><span style="color: #0000FF;">])</span> <span style="color: #008080;">and</span> <span style="color: #004080;">integer</span><span style="color: #0000FF;">(</span><span style="color: #000000;">x</span><span style="color: #0000FF;">[</span><span style="color: #000000;">NEXT</span><span style="color: #0000FF;">]</span> <span style="color: #008080;">and</span> <span style="color: #004080;">integer</span><span style="color: #0000FF;">(</span><span style="color: #000000;">x</span><span style="color: #0000FF;">[</span><span style="color: #000000;">PREV</span><span style="color: #0000FF;">]))</span>

<span style="color: #008080;">end</span> <span style="color: #008080;">type</span>

But more often you would just use the builtin sequences. See also [[Singly-linked_list/Element_definition#Phix|Singly-linked_list/Element_definition]].

With that, 'cddr' can be used to access the next, and 'cadr' to access the

previous element.

(let L (cdr DLst)

(con DLst (cons X L NIL))

# We prepend 'not' to the list in the previous example

For output of the example data, see [[Doubly-linked list/Traversal#PicoLisp]].

=={{header|PL/I}}==

define structure

1 Node,

...

P = P => back_pointer; /* P now points at the previous node. */

=={{header|Plain English}}==

When you define a <code>thing</code>, you are defining a record as a doubly-linked list element. <code>next</code> and <code>previous</code> fields are implicitly added to the record that can be used to build and traverse a list.

=={{header|Pop11}}==

define :class Link;

slot next = [];

slot prev = [];

slot data = [];

=={{header|PureBasic}}==

*prev.node

*next.node

value.i

=={{header|Python}}==

def __init__(self, data = None, prev = None, next = None):

self.prev = prev

while c != None:

yield c

=={{header|Racket}}==

(define-struct dlist (head tail) #:mutable)

(define-struct dlink (content prev next) #:mutable)

See the functions on the [[Doubly-Linked List]] page for the usage of these structures.

(formerly Perl 6)

has DLElem[T] $.prev is rw;

has DLElem[T] $.next is rw;

$!prev.next = $!next; # conveniently returns next element

}

=={{header|REXX}}==

║ @del k,m ─── deletes the M items starting with item K. ║

╚═════════════════════════════════════════════════════════════════════════╝

call sy 'initializing the list.' ; call @init

call sy 'building list: Was it a cat I saw' ; call @put "Was it a cat I saw"

/*──────────────────────────────────────────────────────────────────────────────────────*/

@show: procedure expose $.; parse arg k,m,dir; if dir==-1 & k=='' then k=$.#

'''output'''

<pre>

=={{header|Ruby}}==

Extending [[Singly-Linked List (element)#Ruby]]

attr_accessor :prev

# accessors :succ and :value are inherited

end

=={{header|Rust}}==

=== Simply using the standard library ===

fn main() {

// Doubly linked list containing 32-bit integers

let list = LinkedList::<i32>::new();

=== The behind-the-scenes implementation ===

The standard library uses the (currently) unstable `Shared<T>` type which indicates that the ownership of its contained type has shared ownership. It is guaranteed not to be null, is variant over <code>T</code> (meaning that an <code>&Shared<&'static T></code> may be used where a <code>&Shared<&'a T></code> is expected, indicates to the compiler that it may own a <code>T</code>) and may be dereferenced to a mutable pointer (<code>*mut T</code>). All of the above may be accomplished in standard stable Rust, except for the non-null guarantee which allows the compiler to make a few extra optimizations.

head: Option<Shared<Node<T>>>,

tail: Option<Shared<Node<T>>>,

prev: Option<Shared<Node<T>>>,

element: T,

=={{header|Sidef}}==

data => 'say what',

next => foo_node,

);

=={{header|Swift}}==

class Node<T> {

}

}

=={{header|Tcl}}==

{{eff note|Tcl|list}}

{{works with|Tcl|8.6}} or {{libheader|TclOO}}

variable content next prev

constructor {value {list ""}} {

set prev {*}$args

}

=={{header|Visual Basic .NET}}==

Public Value As T

Public [Next] As Node(Of T)

Public Previous As Node(Of T)

=={{header|Wren}}==

{{libheader|Wren-llist}}

The DNode class in the above module is the element type for the DLinkedList class which is a generic doubly-linked list. The latter is implemented in such a way that the user does not need to deal directly with DNode though for the purposes of the task we show below how instances of it can be created and manipulated.

var dn1 = DNode.new(1)

dn2.next = null

System.print(["node 1", "data = %(dn1.data)", "prev = %(dn1.prev)", "next = %(dn1.next)"])

{{out}}

=={{header|zkl}}==

fcn init(_value,_prev=Void,_next=Void)

{ var value=_value, prev=_prev, next=_next; }

fcn toString{ value.toString() }

a.next=b; b.prev=a;

{{out}}

<pre>