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=={{header|Ada}}==
All that is needed in order to implement this is a common base type. The delegator holds a pointer to an "untyped" object from the base class. Querying if the target implements the delegate interface is done using run-time type identification.
<langsyntaxhighlight lang="ada">with Ada.Text_IO; use Ada.Text_IO;
 
procedure Delegation is
Line 63:
A.Delegate := Has_Thing'Access; -- Set a thing
Put_Line (A.Operation);
end Delegation;</langsyntaxhighlight>
Sample output:
<pre>
Line 70:
delegate implementation
</pre>
 
=={{header|Aikido}}==
<syntaxhighlight lang="aikido">
class Delegator {
public generic delegate = none
 
public function operation {
if (typeof(delegate) == "none") {
return "default implementation"
}
return delegate()
}
}
 
function thing {
return "delegate implementation"
}
 
// default, no delegate
var d = new Delegator()
println (d.operation())
 
// delegate
var d1 = new Delegator()
d1.delegate = thing
println (d1.operation())
 
</syntaxhighlight>
 
=={{header|Aime}}==
<langsyntaxhighlight lang="aime">text
thing(void)
{
Line 113 ⟶ 141:
 
return 0;
}</langsyntaxhighlight>
 
=={{header|Aikido}}==
<lang aikido>
class Delegator {
public generic delegate = none
 
public function operation {
if (typeof(delegate) == "none") {
return "default implementation"
}
return delegate()
}
}
 
function thing {
return "delegate implementation"
}
 
// default, no delegate
var d = new Delegator()
println (d.operation())
 
// delegate
var d1 = new Delegator()
d1.delegate = thing
println (d1.operation())
 
</lang>
 
=={{header|ALGOL 68}}==
As Algol 68 doesn't have classes, we supply a non-OO approximation, similar to the C version.
<langsyntaxhighlight lang="algol68"># An Algol 68 approximation of delegates #
 
# The delegate mode - the delegate is a STRUCT with a single field #
Line 220:
 
)
</syntaxhighlight>
</lang>
{{out}}<pre>
No delegate : default implementation
Delegate with no thing: default implementation
Delegate with a thing : delegate implementation
</pre>
 
 
=={{header|Atari Basic}}==
 
The code does not fully implement all requirements from above.
If you find which requirements have not been met that's great.
What is your proposal to solve that in the code?
 
<syntaxhighlight lang="ataribasic">
10 REM DELEGATION CODE AND EXAMPLE . ATARI BASIC 2020 A. KRESS andreas.kress@hood-group.com
14 REM
15 GOTO 100:REM MAINLOOP
16 REM
20 REM DELEGATOR OBJECT
21 REM
30 IF DELEGATE THEN GOSUB DELEGATE:GOTO 56
35 REM
50 REM DELEGATOR HAS TO DO THE JOB
55 PRINT "DEFAULT IMPLEMENTATION - DONE BY DELEGATOR"
56 RETURN
60 REM CALL DELEGATE
65 GOSUB DELEGATOR
66 RETURN
79 REM
80 REM DELEGATE OBJECT
81 REM
90 PRINT "DELEGATE IMPLEMENTATION - DONE BY DELEGATE"
91 RETURN
99 REM
100 REM MAINLOOP - DELEGATION EXAMPLE
101 REM
110 DELEGATE=0:REM NO DELEGATE
120 GOSUB 20:REM INIT DELEGATOR
130 DELEGATE=80:REM DELEGATE IS
140 GOSUB 20:REM INIT DELEGATOR
</syntaxhighlight>
{{out}}<pre>
RUN
DEFAULT IMPLEMENTATION - DONE BY DELEGATOR
DELEGATE IMPLEMENTATION - DONE BY DELEGATE
 
Ready
</pre>
 
=={{header|C}}==
As best you can do, without support for classes.
<langsyntaxhighlight lang="c">#include <stdio.h>
#include <stdlib.h>
#include <string.h>
Line 314 ⟶ 357:
Delegator_Operation( theDelegator, 3, del2));
return 0;
}</langsyntaxhighlight>
 
=={{header|C sharp|C#}}==
<langsyntaxhighlight lang="csharp">using System;
 
interface IOperable
Line 355 ⟶ 398:
}
}
}</langsyntaxhighlight>
Output:
<pre>Default implementation.
Line 364 ⟶ 407:
Delegates in the C# or D style are available in C++ through std::tr1::function class template. These delegates don't exactly match this problem statement though, as they only support a single method call (which is operator()), and so don't support querying for support of particular methods.
 
<syntaxhighlight lang="cpp">
<lang Cpp>
#include <tr1/memory>
#include <string>
Line 444 ⟶ 487:
*/
}
</syntaxhighlight>
</lang>
 
=={{header|Clojure}}==
<langsyntaxhighlight lang="clojure">(defprotocol Thing
(thing [_]))
 
Line 458 ⟶ 502:
(defrecord Delegate []
Thing
(thing [_] "delegate implementation"))</langsyntaxhighlight>
 
{{out}}
Line 477 ⟶ 521:
=={{header|CoffeeScript}}==
{{trans|Python}}
<langsyntaxhighlight lang="coffeescript">
class Delegator
operation: ->
Line 502 ⟶ 546:
testDelegator()
</syntaxhighlight>
</lang>
output
<syntaxhighlight lang="text">
> coffee foo.coffee
default implementation
default implementation
Delegate Implementation
</syntaxhighlight>
</lang>
 
=={{header|Common Lisp}}==
Line 516 ⟶ 560:
In CLOS, methods exist apart from classes, and are specialized based on the types of their arguments. This example defines two classes (delegator and delegate), and a thing generic method which is specialized in three ways: (1) for 'any' argument, providing a default method; (2) for delegators, where thing is recursively applied to the delegator's delegate (if there is one); and (3) for delegates.
 
<langsyntaxhighlight lang="lisp">(defgeneric thing (object)
(:documentation "Thing the object."))
 
Line 544 ⟶ 588:
(assert (string= "no delegate" (thing d1)))
(assert (string= "default implementation" (thing d2)))
(assert (string= "delegate implementation" (thing d3))))</langsyntaxhighlight>
 
=={{header|D}}==
Line 550 ⟶ 594:
''Delegate'' object and pass a real delegate directly to '''Delegator'''.
 
<langsyntaxhighlight lang="d">class Delegator {
string delegate() hasDelegate;
 
Line 573 ⟶ 617:
writeln(dr.operation());
writeln(dr.setDg(thing).operation());
}</langsyntaxhighlight>
{{out}}
<pre>Default implementation
Line 581 ⟶ 625:
===Version using Tango===
{{libheader|tango}}
<langsyntaxhighlight lang="d">import tango.io.Stdout;
 
class Delegator
Line 609 ⟶ 653:
Stdout ( dr.setDg(thing).operation ).newline;
return 0;
}</langsyntaxhighlight>
 
=={{header|Dart}}==
I didn't find a way to check for existing methods, so the version with Object doesn't work yet. The code is adapted from the Java version, but using var instead of an Interface
<langsyntaxhighlight lang="dart">class Delegator {
var delegate;
Line 641 ⟶ 685:
a.delegate = d;
Expect.equals("delegate implementation",a.operation());
}</langsyntaxhighlight>
 
=={{header|Delphi}}==
Translation of the Java example found at [http://en.wikipedia.org/wiki/Delegation_pattern Wikipedia].
<langsyntaxhighlight Delphilang="delphi">unit Printer;
 
interface
Line 694 ⟶ 738:
end;
 
end.</langsyntaxhighlight>
<langsyntaxhighlight Delphilang="delphi">program Delegate;
 
{$APPTYPE CONSOLE}
Line 713 ⟶ 757:
PrinterObj.Free;
end;
end.</langsyntaxhighlight>
 
=={{header|E}}==
 
<langsyntaxhighlight lang="e">def makeDelegator {
/** construct without an explicit delegate */
to run() {
Line 750 ⟶ 794:
> })
> delegator.operation()
# value: "default implementation"</langsyntaxhighlight>
 
 
=={{header|Elena}}==
ELENA 36.4x :
 
Using multi methods:
<langsyntaxhighlight lang="elena">import extensions.;
import system'routines.;
interface IOperable
{
abstract operate []();
}
class Operable :: IOperable
{
constructor() new []{}
operate()
= "delegate implementation".;
}
class Delegator
{
object theDelegate.;
set Delegate:object
[
if(nil == object)
[
theDelegate := nilValue.
];
[
theDelegate := object.
]
]
privateset operateDelegate(object operable)
{
= "default implementation".
theDelegate := object
}
privateinternal operate(IOperable operable)
= operable"default operate.implementation";
internal operate(IOperable operable)
<= operable.operate(theDelegate).;
operate()
<= operate(theDelegate);
}
public program()
{
[
var delegator := Delegator new. Delegator();
(new object[]{nil, new Object(), new, Operable new() }.forEach(::(o)
[{
delegator .Delegate := o.;
console .printLine(delegator .operate()).
].}
}</syntaxhighlight>
]</lang>
Generic solution:
<langsyntaxhighlight lang="elena">import extensions.;
import system'routines.;
 
class Operable
{
operableOperable = self.;
operate()
= "delegate implementation".;
}
class Delegator
{
object prop Delegate :: theDelegate.prop;
constructor new()
[{
theDelegateDelegate := nil.
]}
operate()
[{
// if the object does not support "get&operableOperable" message - returns nil
var anOperableoperable := theDelegate operableDelegate.Operable \ back:(nil.);
if (nil == anOperableoperable)
[{
^ "default implementation".
];}
[else
^ anOperable operate.{
] ^ operable.operate()
] }
}
}
public program ()
{
[
var delegator := Delegator new. Delegator();
(new object[]{nil, new Object(), new, Operable new() }.forEach(::(o)
[{
delegator .Delegate := o.;
console .printLine(delegator .operate()).
].}
}</syntaxhighlight>
]</lang>
{{out}}
<pre>
Line 862 ⟶ 900:
delegate implementation
</pre>
 
=={{header|FreeBASIC}}==
{{trans|Phix}}
FreeBASIC does not directly support objects or delegation functions. However, you can achieve similar functionality using user-defined types and function pointers.
<syntaxhighlight lang="vbnet">
Type Objeto
operation As Function() As String
other As String
End Type
 
Function xthing() As String
Return "default implementation"
End Function
 
Function newX() As Objeto
Dim As Objeto o
o.operation = @xthing
Return o
End Function
 
Function newY() As Objeto
Dim As Objeto o = newX()
o.other = "something else"
o.operation = 0 ' remove delegate
Return o
End Function
 
Function zthing() As String
Return "delegate implementation"
End Function
 
Function newZ() As Objeto
Dim As Objeto o = newX()
o.operation = @zthing ' replace delegate
Return o
End Function
 
Function operation(o As Objeto) As String
Return Iif(o.operation <> 0, o.operation(), "no implementation")
End Function
 
Dim As Objeto x = newX()
Dim As Objeto y = newY()
Dim As Objeto z = newZ()
 
Print operation(x)
Print operation(y)
Print operation(z)
 
Sleep</syntaxhighlight>
{{out}}
<pre>Similar as Phix entry.</pre>
 
=={{header|F_Sharp|F#}}==
<langsyntaxhighlight lang="fsharp">type Delegator() =
let defaultOperation() = "default implementation"
let mutable del = null
Line 889 ⟶ 979:
 
d.Delegate <- new Delegate()
assert (d.operation() = "delegate implementation")</langsyntaxhighlight>
 
=={{header|Forth}}==
Line 897 ⟶ 987:
Needs the FMS-SI (single inheritance) library code located here:
http://soton.mpeforth.com/flag/fms/index.html
<langsyntaxhighlight lang="forth">include FMS-SI.f
 
:class delegate
Line 931 ⟶ 1,021:
slave master !:
master operation \ => delegate implementation
</syntaxhighlight>
</lang>
 
=={{header|Go}}==
 
<langsyntaxhighlight lang="go">package main
import "fmt"
 
Line 973 ⟶ 1,063:
a.delegate = d
fmt.Println(a.operation()) // prints "delegate implementation"
}</langsyntaxhighlight>
 
=={{header|Io}}==
{{trans|Python}}
<langsyntaxhighlight Iolang="io">Delegator := Object clone do(
delegate ::= nil
operation := method(
Line 998 ⟶ 1,088:
 
a setDelegate(Delegate clone)
a operation println</langsyntaxhighlight>
{{out}}
<pre>default implementation
Line 1,008 ⟶ 1,098:
Life becomes slightly cleaner if we delegate to ourselves in the absence of some other delegate.
 
<langsyntaxhighlight Jlang="j">coclass 'delegator'
operation=:3 :'thing__delegate ::thing y'
thing=: 'default implementation'"_
Line 1,020 ⟶ 1,110:
 
NB. set context in case this script was used interactively, instead of being loaded
cocurrent 'base'</langsyntaxhighlight>
 
Example use:
 
<langsyntaxhighlight Jlang="j"> obj=:conew'delegator'
operation__obj''
default implementation
Line 1,038 ⟶ 1,128:
└─┘
operation__obj''
delegate implementation</langsyntaxhighlight>
 
=={{header|Java}}==
This implementation uses an interface called Thingable to specify the type of delegates that respond to thing(). The downside is that any delegate you want to use has to explicitly declare to implement the interface. The upside is that the type system guarantees that when the delegate is non-null, it must implement the "thing" method.
 
<langsyntaxhighlight lang="java">interface Thingable {
String thing();
}
Line 1,085 ⟶ 1,175:
assert a.operation().equals("anonymous delegate implementation");
}
}</langsyntaxhighlight>
 
{{works with|Java|8+}}
<langsyntaxhighlight lang="java">package delegate;
 
@FunctionalInterface
public interface Thingable {
public String thing();
}</langsyntaxhighlight>
 
<langsyntaxhighlight lang="java">package delegate;
 
import java.util.Optional;
Line 1,113 ⟶ 1,203:
;
}
}</langsyntaxhighlight>
 
<langsyntaxhighlight lang="java">package delegate;
 
@FunctionalInterface
Line 1,131 ⟶ 1,221:
return () -> thingable;
}
}</langsyntaxhighlight>
 
<langsyntaxhighlight lang="java">package delegate;
 
public final class Delegate implements Thingable {
Line 1,140 ⟶ 1,230:
return "delegate implementation";
}
}</langsyntaxhighlight>
 
<langsyntaxhighlight lang="java">package delegate;
 
// Example usage
Line 1,177 ⟶ 1,267:
assert d5.operation().equals("lambda expression implementation");
}
}</langsyntaxhighlight>
 
=={{header|JavaScript}}==
{{trans|Python}}
<langsyntaxhighlight lang="javascript">function Delegator() {
this.delegate = null ;
this.operation = function(){
Line 1,205 ⟶ 1,295:
a.delegate = new Delegate() ;
document.write(a.operation() + "\n") ;
}</langsyntaxhighlight>
 
=={{header|Julia}}==
'''Module''':
<langsyntaxhighlight lang="julia">module Delegates
 
export Delegator, Delegate
Line 1,223 ⟶ 1,313:
thing(::Delegate) = "delegate implementation"
 
end # module Delegates</langsyntaxhighlight>
 
'''Main''':
<langsyntaxhighlight lang="julia">using .Delegates
 
a = Delegator(nothing)
Line 1,236 ⟶ 1,326:
@show Delegates.operation(a)
@show Delegates.operation(b)
@show Delegates.operation(c)</langsyntaxhighlight>
 
{{out}}
Line 1,247 ⟶ 1,337:
 
The first two scenarios are not therefore strictly possible though the second can be simulated by passing a 'responds' parameter to the delegate class constructor.
<langsyntaxhighlight lang="scala">// version 1.1.51
 
interface Thingable {
Line 1,271 ⟶ 1,361:
val dd2 = Delegator(d2)
println(dd2.operation())
}</langsyntaxhighlight>
 
{{out}}
Line 1,278 ⟶ 1,368:
delegate implementation
</pre>
 
=={{header|Latitude}}==
 
{{trans|Python}}
<syntaxhighlight lang="latitude">Delegator ::= Object clone tap {
self delegate := Nil.
self clone := {
Parents above (parent self, 'clone) call tap {
self delegate := #'(self delegate).
}.
}.
self operation := {
localize.
if { this delegate slot? 'thing. } then {
this delegate thing.
} else {
"default implementation".
}.
}.
}.
 
Delegate ::= Object clone tap {
self thing := "delegate implementation".
}.
 
;; No delegate
foo := Delegator clone.
println: foo operation. ;; "default implementation"
 
;; Delegate which lacks `thing`
foo delegate := Object.
println: foo operation. ;; "default implementation"
 
;; Delegate which implements `thing`
foo delegate := Delegate.
println: foo operation. ;; "delegate implementation"</syntaxhighlight>
 
=={{header|Logtalk}}==
We use prototypes instead of classes for simplicity.
<langsyntaxhighlight lang="logtalk">% define a category for holding the interface
% and implementation for delegator objects
 
Line 1,356 ⟶ 1,482:
a_delegator::operation(String3),
String3 == 'delegate implementation'
)).</langsyntaxhighlight>
 
=={{header|Lua}}==
<syntaxhighlight lang="lua">local function Delegator()
return {
operation = function(self)
if (type(self.delegate)=="table") and (type(self.delegate.thing)=="function") then
return self.delegate:thing()
else
return "default implementation"
end
end
}
end
 
local function Delegate()
return {
thing = function(self)
return "delegate implementation"
end
}
end
 
local function NonDelegate(which)
if (which == 1) then return true -- boolean
elseif (which == 2) then return 12345 -- number
elseif (which == 3) then return "Hello" -- string
elseif (which == 4) then return function() end -- function
elseif (which == 5) then return { nothing = function() end } -- table (without "thing")
elseif (which == 6) then return coroutine.create(function() end) -- thread
elseif (which == 7) then return io.open("delegates.lua","r") -- userdata (if exists, or nil)
end
end
 
-- WITH NO (NIL) DELEGATE
local d = Delegator()
assert(d:operation() == "default implementation")
 
-- WITH A NON-DELEGATE
for i = 1, 7 do
d.delegate = NonDelegate(i)
assert(d:operation() == "default implementation")
end
 
-- WITH A PROPER DELEGATE
d.delegate = Delegate()
assert(d:operation() == "delegate implementation")
 
print("pass")</syntaxhighlight>
 
=={{header|M2000 Interpreter}}==
<syntaxhighlight lang="m2000 interpreter">
<lang M2000 Interpreter>
Module Checkit {
\\ there are some kinds of objects in M2000, one of them is the Group, the user object
Line 1,467 ⟶ 1,641:
Checkit
 
</syntaxhighlight>
</lang>
{{out}}
<pre>
Line 1,498 ⟶ 1,672:
 
=={{header|Mathematica}} / {{header|Wolfram Language}}==
<langsyntaxhighlight Mathematicalang="mathematica">delegator[del_]@operate :=
If[StringQ[del@operate], del@operate, "default implementation"];
del1 = Null;
del2@banana = "phone";
del3@operate = "delegate implementation";
Print[delegator[#]@operate] & /@ {del1, del2, del3};</langsyntaxhighlight>
{{out}}
<pre>default implementation
Line 1,510 ⟶ 1,684:
 
=={{header|NGS}}==
<syntaxhighlight lang="ngs">{
<lang NGS>{
type Delegator
 
Line 1,549 ⟶ 1,723:
echo(a.operation())
}</langsyntaxhighlight>
{{out}}
<pre>default implementation
default implementation
delegate implementation</pre>
 
=={{header|Nim}}==
<syntaxhighlight lang="nim">####################################################################################################
# Base delegate.
 
type Delegate = ref object of RootObj
nil
 
method thing(d: Delegate): string {.base.} =
## Default implementation of "thing".
## Using a method rather than a proc allows dynamic dispatch.
"default implementation"
 
 
####################################################################################################
# Delegator.
 
type Delegator = object
delegate: Delegate
 
proc initDelegator(d: Delegate = nil): Delegator =
## Create a delegator with given delegate or nil.
if d.isNil:
Delegator(delegate: Delegate()) # Will use a default delegate instance.
else:
Delegator(delegate: d) # Use the provided delegate instance.
 
proc operation(d: Delegator): string =
## Calls the delegate.
d.delegate.thing()
 
 
####################################################################################################
# Usage.
 
let d = initDelegator()
echo "Without any delegate: ", d.operation()
 
type Delegate1 = ref object of Delegate
 
let d1 = initDelegator(Delegate1())
echo "With a delegate which desn’t provide the “thing” method: ", d1.operation()
 
type Delegate2 = ref object of Delegate
 
method thing(d: Delegate2): string =
"delegate implementation"
 
let d2 = initDelegator(Delegate2())
echo "With a delegate which provided the “thing” method: ", d2.operation()</syntaxhighlight>
 
{{out}}
<pre>Without any delegate: default implementation
With a delegate which desn’t provide the “thing” method: default implementation
With a delegate which provided the “thing” method: delegate implementation</pre>
 
=={{header|Objeck}}==
{{trans|Java}}
<syntaxhighlight lang="objeck">interface Thingable {
method : virtual : public : Thing() ~ String;
}
class Delegator {
@delegate : Thingable;
 
New() {
}
 
method : public : SetDelegate(delegate : Thingable) ~ Nil {
@delegate := delegate;
}
 
method : public : Operation() ~ String {
if(@delegate = Nil) {
return "default implementation";
}
else {
return @delegate->Thing();
};
}
}
 
class Delegate implements Thingable {
New() {
}
 
method : public : Thing() ~ String {
return "delegate implementation";
}
}
 
class Example {
function : Main(args : String[]) ~ Nil {
# Without a delegate:
a := Delegator->New();
Runtime->Assert(a->Operation()->Equals("default implementation"));
# With a delegate:
d := Delegate->New();
a->SetDelegate(d);
Runtime->Assert(a->Operation()->Equals("delegate implementation"));
 
# Same as the above, but with an anonymous class:
a->SetDelegate(Base->New() implements Thingable {
method : public : Thing() ~ String {
return "anonymous delegate implementation";
}
});
 
Runtime->Assert(a->Operation()->Equals("anonymous delegate implementation"));
}
}
</syntaxhighlight>
 
=={{header|Objective-C}}==
Line 1,559 ⟶ 1,846:
{{works with|Cocoa}}
{{works with|GNUstep}}
<langsyntaxhighlight lang="objc">#import <Foundation/Foundation.h>
 
@interface Delegator : NSObject {
Line 1,634 ⟶ 1,921:
 
return 0;
}</langsyntaxhighlight>
 
Objective-C 2.0, modern runtime, Automatic Reference Counting, Autosynthesize (LLVM 4.0+)
{{works with|Cocoa}}
 
<langsyntaxhighlight lang="objc">#import <Foundation/Foundation.h>
 
// Formal protocol for the delegate
Line 1,683 ⟶ 1,970:
}
return 0;
}</langsyntaxhighlight>
 
 
=={{header|Oforth}}==
<langsyntaxhighlight Oforthlang="oforth">Object Class new: Delegate1
Object Class new: Delegate2
Line 1,697 ⟶ 1,983:
Delegator method: operation
@delegate respondTo(#thing) ifTrue: [ @delegate thing return ]
"Default implementation" println ;</langsyntaxhighlight>
Usage :
 
<langsyntaxhighlight Oforthlang="oforth">Delegator new(null) operation
Default implementation
 
Line 1,707 ⟶ 1,993:
 
Delegator new(Delegate2 new) operation
Delegate implementation</langsyntaxhighlight>
 
=={{header|ooRexx}}==
<syntaxhighlight lang="oorexx">
<lang ooRexx>
delegator = .delegator~new -- no delegate
say delegator~operation
Line 1,751 ⟶ 2,037:
nomethod:
return "default implementation"
</syntaxhighlight>
</lang>
 
=={{header|OxygenBasic}}==
<langsyntaxhighlight lang="oxygenbasic">
class DelegateA 'not implmenting thing()
'==============
Line 1,799 ⟶ 2,085:
print dgr.thing 'result "not using Delegate"
print dg.thing 'result "Delegate Implementation"
</syntaxhighlight>
</lang>
 
=={{header|Oz}}==
{{trans|Python}}
<langsyntaxhighlight lang="oz">declare
class Delegator from BaseObject
attr
Line 1,845 ⟶ 2,131:
 
{A set({New Delegate noop})}
{System.showInfo {A operation($)}}</langsyntaxhighlight>
 
=={{header|Pascal}}==
Line 1,852 ⟶ 2,138:
=={{header|Perl}}==
{{trans|Python}}
<langsyntaxhighlight lang="perl">use strict;
 
package Delegator;
Line 1,890 ⟶ 2,176:
$a->{delegate} = Delegate->new;
$a->operation eq 'delegate implementation' or die;
</syntaxhighlight>
</lang>
 
Using Moose.
 
<langsyntaxhighlight lang="perl">
use 5.010_000;
 
Line 1,950 ⟶ 2,236:
$delegator->operation eq 'delegate implementation' or die;
 
</syntaxhighlight>
</lang>
 
=={{header|Perl 6}}==
<lang perl6>class Non-Delegate { }
 
class Delegate {
method thing {
return "delegate implementation"
}
}
 
class Delegator {
has $.delegate is rw;
 
method operation {
$.delegate.^can( 'thing' ) ?? $.delegate.thing
!! "default implementation"
}
}
 
my Delegator $d .= new;
 
say "empty: "~$d.operation;
 
$d.delegate = Non-Delegate.new;
 
say "Non-Delegate: "~$d.operation;
 
$d.delegate = Delegate.new;
 
say "Delegate: "~$d.operation;</lang>
 
=={{header|Phix}}==
Line 1,986 ⟶ 2,242:
I will admit that the whole concept of "no delegate/with one that does not implement" makes no sense whatsoever to me.<br>
While I've shown this using a single rid, you could of course hold an entire sequence of them or even better a dictionary and use named lookups for rids in that.
<langsyntaxhighlight Phixlang="phix">enum OTHER, OPERATION
 
function operation(object o)
Line 2,029 ⟶ 2,285:
?operation(x)
?operation(y)
?operation(z)</langsyntaxhighlight>
 
{{out}}
Line 2,038 ⟶ 2,294:
</pre>
Obviously, you can explictly test for rid=NULL as shown, or remove that test and catch exceptions, ie:
<langsyntaxhighlight Phixlang="phix">?operation(x)
try -- (since rid=NULL check commented out)
?operation(y)
Line 2,044 ⟶ 2,300:
?"oops, no implementation"
end try
?operation(z)</langsyntaxhighlight>
 
=={{header|PHP}}==
{{trans|Python}}
<langsyntaxhighlight lang="php">class Delegator {
function __construct() {
$this->delegate = NULL ;
Line 2,072 ⟶ 2,328:
 
$a->delegate = new Delegate() ;
print "{$a->operation()}\n" ;</langsyntaxhighlight>
 
=={{header|PicoLisp}}==
<langsyntaxhighlight PicoLisplang="picolisp">(class +Delegator)
# delegate
 
Line 2,104 ⟶ 2,360:
# With delegate that implements 'thing>'
(put A 'delegate (new '(+Delegate) "delegate implementation"))
(println (operation> A)) )</langsyntaxhighlight>
Output:
<pre>"default implementation"
Line 2,111 ⟶ 2,367:
 
=={{header|Pop11}}==
<langsyntaxhighlight lang="pop11">uses objectclass;
define :class Delegator;
slot delegate = false;
Line 2,142 ⟶ 2,398:
;;; delegating to a freshly created Delegate
newDelegate() -> delegate(a);
operation(a) =></langsyntaxhighlight>
 
=={{header|Python}}==
<langsyntaxhighlight lang="python">class Delegator:
def __init__(self):
self.delegate = None
Line 2,169 ⟶ 2,425:
# With delegate that implements "thing"
a.delegate = Delegate()
assert a.operation() == 'delegate implementation'</langsyntaxhighlight>
 
=={{header|Racket}}==
Line 2,181 ⟶ 2,437:
follows the requirement of the task better.
 
<langsyntaxhighlight lang="racket">#lang racket
;; Delegates. Tim Brown 2014-10-16
 
Line 2,215 ⟶ 2,471:
(send delegator-2 operation) => "delegate implementation"
(send (new delegator% [delegate thinging-delegate]) operation) => "delegate implementation"))
</syntaxhighlight>
</lang>
 
All the tests pass. Believe me.
 
=={{header|Raku}}==
(formerly Perl 6)
<syntaxhighlight lang="raku" line>class Non-Delegate { }
 
class Delegate {
method thing {
return "delegate implementation"
}
}
 
class Delegator {
has $.delegate is rw;
 
method operation {
$.delegate.^can( 'thing' ) ?? $.delegate.thing
!! "default implementation"
}
}
 
my Delegator $d .= new;
 
say "empty: "~$d.operation;
 
$d.delegate = Non-Delegate.new;
 
say "Non-Delegate: "~$d.operation;
 
$d.delegate = Delegate.new;
 
say "Delegate: "~$d.operation;</syntaxhighlight>
 
=={{header|Ruby}}==
{{trans|Python}}
<langsyntaxhighlight lang="ruby">class Delegator
attr_accessor :delegate
def operation
Line 2,251 ⟶ 2,538:
a.delegate = Delegate.new
puts a.operation # prints "delegate implementation"
end</langsyntaxhighlight>
 
Using Forwardable lib
 
<langsyntaxhighlight lang="ruby">require 'forwardable'
 
class Delegator; extend Forwardable
Line 2,274 ⟶ 2,561:
a = Delegator.new
puts a.delegated # prints "Delegate"
</syntaxhighlight>
</lang>
 
=={{header|Rust}}==
Requiring delegates to implement Thingable:
<langsyntaxhighlight Rustlang="rust">trait Thingable {
fn thing(&self) -> &str;
}
Line 2,304 ⟶ 2,591:
let d: Delegator<Delegate> = Delegator(Some(Delegate {}));
println!("{}", d.thing());
}</langsyntaxhighlight>
{{Out}}
<pre>Default implmementation
Line 2,310 ⟶ 2,597:
 
Using nightly-only specialization feature:
<langsyntaxhighlight Rustlang="rust">#![feature(specialization)]
 
trait Thingable {
Line 2,350 ⟶ 2,637:
let d: Delegator<Delegate> = Delegator(Some(Delegate {}));
println!("{}", d.thing());
}</langsyntaxhighlight>
{{Out}}
<pre>Default implementation
Line 2,359 ⟶ 2,646:
=={{header|Scala}}==
{{Out}}Best seen running in your browser either by [https://scalafiddle.io/sf/cCYD9tQ/0 ScalaFiddle (ES aka JavaScript, non JVM)] or [https://scastie.scala-lang.org/2TWYJifpTuOVhrAfWP51oA Scastie (remote JVM)].
<langsyntaxhighlight Scalalang="scala">trait Thingable {
def thing: String
}
Line 2,390 ⟶ 2,677:
assert(a.operation == "anonymous delegate implementation")
 
}</langsyntaxhighlight>
 
=={{header|Sidef}}==
<langsyntaxhighlight lang="ruby">class NonDelegate { }
 
class Delegate {
Line 2,416 ⟶ 2,704:
say "NonDelegate: #{d.operation}"
d.delegate = Delegate()
say "Delegate: #{d.operation}"</langsyntaxhighlight>
{{out}}
empty: default implementation
NonDelegate: default implementation
Delegate: delegate implementation
 
=={{header|Smalltalk}}==
{{works with|Smalltalk/X}}
Definition of the thingy:
<syntaxhighlight lang="smalltalk">Object
subclass:#Thingy
instanceVariableNames:''
 
thing
^ 'thingy implementation'</syntaxhighlight>
Definition of the delegator:
<syntaxhighlight lang="smalltalk">Object
subclass:#Delegator
instanceVariableNames:'delegate'
 
delegate:something
delegate := something
 
operation
^ delegate
perform:#thing ifNotUnderstood:'default implementation'.</syntaxhighlight>
Sample use:
<syntaxhighlight lang="smalltalk">|d|
d := Delegator new.
d operation.
-> 'default implementation'
 
d delegate:(Thingy new).
d operation.
-> 'thingy implementation'</syntaxhighlight>
 
=={{header|Swift}}==
Allowing the delegate to be any type and taking advantage of dynamism of method lookup:
<langsyntaxhighlight lang="swift">import Foundation
 
protocol Thingable { // prior to Swift 1.2, needs to be declared @objc
Line 2,456 ⟶ 2,774:
let d = Delegate()
a.delegate = d
println(a.operation()) // prints "delegate implementation"</langsyntaxhighlight>
 
 
Alternately, requiring the delegate to conform to a given protocol:
<langsyntaxhighlight lang="swift">protocol Thingable : class {
func thing() -> String
}
Line 2,486 ⟶ 2,804:
let d = Delegate()
a.delegate = d
println(a.operation()) // prints "delegate implementation"</langsyntaxhighlight>
 
=={{header|Tcl}}==
{{works with|Tcl|8.6}} or {{libheader|TclOO}}
Uses [[Assertions#Tcl]]
<langsyntaxhighlight lang="tcl">package require TclOO
 
oo::class create Delegate {
Line 2,543 ⟶ 2,861:
assert {[a operation] ne "default implementation"}
 
puts "all assertions passed"</langsyntaxhighlight>
 
To code the <code>operation</code> method without relying on catching an exception, but strictly by using introspection:
<langsyntaxhighlight lang="tcl">method operation {} {
if { [info exists delegate] &&
[info object isa object $delegate] &&
Line 2,555 ⟶ 2,873:
set result "default implementation"
}
}</langsyntaxhighlight>
 
=={{header|TXR}}==
 
<syntaxhighlight lang="txrlisp">;; TXR Lisp's :delegate implementation is hard delegation: the indicated
;; delegate object must exist and take the method call. To do soft
;; delegation, we develop a macro (delegate-or-fallback x y z)
;; which chooses x if x is an object which supports a z method,
;; or else chooses y.
 
(defun delegate-or-fallback-impl (del-inst fb-inst required-meth)
(let (del-type)
(if (and (structp del-inst)
(set del-type (struct-type del-inst))
(static-slot-p del-type required-meth)
(functionp (static-slot del-type required-meth)))
del-inst
fb-inst)))
 
(defmacro delegate-or-fallback (delegate-expr fallback-obj : required-meth)
^(delegate-or-fallback-impl ,delegate-expr ,fallback-obj ',required-meth))
 
;; With the above, we can use the defstruct delegate clause syntax:
;;
;; (:delegate source-method (obj) target-obj target-method)
;;
;; which writes a delegate method called source-method, that delegates
;; to target-method on target-obj. We calculate target-obj using
;; our macro and ensure that the delegator itself imlpements target-method.
 
(defstruct delegator ()
delegate
(:delegate operation (me) (delegate-or-fallback me.delegate me thing) thing)
 
(:method thing (me)
"default implementation"))
 
(defstruct delegate ()
(:method thing (me)
"delegate implementation"))
 
;; Tests:
 
;; no delegate
(prinl (new delegator).(operation))
 
;; struct delegate, but not with thing method
(prinl (new delegator delegate (new time)).(operation))
 
;; delegate with thing method
(prinl (new delegator delegate (new delegate)).(operation))</syntaxhighlight>
 
{{out}}
 
<pre>"default implementation"
"default implementation"
"delegate implementation"</pre>
 
=={{header|Vorpal}}==
Delegate objects can be an array of delegates or as a single delegate.
<langsyntaxhighlight lang="vorpal">a = new()
a.f = method(){
.x.print()
Line 2,582 ⟶ 2,956:
d.delegate = a
d.x = 7
d.f()</langsyntaxhighlight>
 
The resulting output:
Line 2,589 ⟶ 2,963:
4
7
</pre>
 
=={{header|Wren}}==
Wren is dynamically typed so we can plug any kind of delegate into the Delegator.
<syntaxhighlight lang="wren">class Thingable {
thing { }
}
 
// Delegate that doesn't implement Thingable
class Delegate {
construct new() { }
}
 
// Delegate that implements Thingable
class Delegate2 is Thingable {
construct new() { }
 
thing { "delegate implementation" }
}
 
class Delegator {
construct new() {
_delegate = null
}
 
delegate { _delegate }
delegate=(d) { _delegate = d }
 
operation {
if (!_delegate || !(_delegate is Thingable)) return "default implementation"
return _delegate.thing
}
}
 
// without a delegate
var d = Delegator.new()
System.print(d.operation)
 
// with a delegate that doesn't implement Thingable
d.delegate = Delegate.new()
System.print(d.operation)
 
// with a delegate that does implement Thingable
d.delegate = Delegate2.new()
System.print(d.operation)</syntaxhighlight>
 
{{out}}
<pre>
default implementation
default implementation
delegate implementation
</pre>
 
=={{header|zkl}}==
{{trans|Scala}}
<langsyntaxhighlight lang="zkl">class Thingable{ var thing; }
class Delegator{
Line 2,603 ⟶ 3,028:
}
class Delegate(Thingable){ thing = "delegate implementation" }</langsyntaxhighlight>
<langsyntaxhighlight lang="zkl"> // Without a delegate:
a:= Delegator();
a.operation().println(); //--> "default implementation"
Line 2,611 ⟶ 3,036:
// With a delegate:
a.delegate = Delegate();
a.operation().println(); //-->"delegate implementation"</langsyntaxhighlight>
A second example
<langsyntaxhighlight lang="zkl">class [static] Logger{ // Only one logging resource
var [mixin=File] dst; // File like semantics, eg Data, Pipe
dst = File.DevNull;
// initially, the logger does nothing
fcn log(msg){dst.writeln(vm.pasteArgs())}
}</langsyntaxhighlight>
 
<langsyntaxhighlight lang="zkl">Logger.log("this is a test"); //-->nada
Logger.dst=Console;
Logger.log("this is a test 2"); //-->writes to Console
 
class B(Logger){ log("Hello from ",self,"'s constructor"); }
B(); //-->Hello from Class(B)'s constructor</langsyntaxhighlight>
 
The base class B was constructed at startup,
Jjuanhdez
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