Delegates: Difference between revisions

=={{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.

 

procedure Delegation is

A.Delegate := Has_Thing'Access; -- Set a thing

Put_Line (A.Operation);

Sample output:

<pre>

delegate implementation

</pre>

 

=={{header|Aime}}==

thing(void)

{

 

return 0;

 

 

 

 

 

 

 

=={{header|C}}==

As best you can do, without support for classes.

#include <stdlib.h>

#include <string.h>

Delegator_Operation( theDelegator, 3, del2));

return 0;

 

 

interface IOperable

}

}

Output:

<pre>Default implementation.

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.

 

#include <tr1/memory>

#include <string>

*/

}

=={{header|CoffeeScript}}==

{{trans|Python}}

class Delegator

operation: ->

testDelegator()

output

> coffee foo.coffee

default implementation

default implementation

Delegate Implementation

 

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

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.

 

(:documentation "Thing the object."))

 

(assert (string= "no delegate" (thing d1)))

(assert (string= "default implementation" (thing d2)))

 

=={{header|D}}==

''Delegate'' object and pass a real delegate directly to '''Delegator'''.

 

string delegate() hasDelegate;

 

writeln(dr.operation());

writeln(dr.setDg(thing).operation());

{{out}}

<pre>Default implementation

===Version using Tango===

{{libheader|tango}}

 

class Delegator

Stdout ( dr.setDg(thing).operation ).newline;

return 0;

 

=={{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

var delegate;

a.delegate = d;

Expect.equals("delegate implementation",a.operation());

 

=={{header|Delphi}}==

Translation of the Java example found at [http://en.wikipedia.org/wiki/Delegation_pattern Wikipedia].

 

interface

end;

 

 

{$APPTYPE CONSOLE}

PrinterObj.Free;

end;

 

=={{header|E}}==

 

/** construct without an explicit delegate */

to run() {

> })

> delegator.operation()

 

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

let defaultOperation() = "default implementation"

let mutable del = null

 

d.Delegate <- new Delegate()

 

=={{header|Go}}==

 

import "fmt"

 

a.delegate = d

fmt.Println(a.operation()) // prints "delegate implementation"

 

=={{header|J}}==

Life becomes slightly cleaner if we delegate to ourselves in the absence of some other delegate.

 

operation=:3 :'thing__delegate ::thing y'

thing=: 'default implementation'"_

 

NB. set context in case this script was used interactively, instead of being loaded

 

Example use:

 

operation__obj''

default implementation

└─┘

operation__obj''

 

=={{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.

 

String thing();

}

assert a.operation().equals("anonymous delegate implementation");

}

 

{{works with|Java|8+}}

 

@FunctionalInterface

public interface Thingable {

public String thing();

 

 

import java.util.Optional;

;

}

 

 

@FunctionalInterface

return () -> thingable;

}

 

 

public final class Delegate implements Thingable {

return "delegate implementation";

}

 

 

// Example usage

assert d5.operation().equals("lambda expression implementation");

}

 

=={{header|JavaScript}}==

{{trans|Python}}

this.delegate = null ;

this.operation = function(){

a.delegate = new Delegate() ;

document.write(a.operation() + "\n") ;

 

=={{header|Logtalk}}==

We use prototypes instead of classes for simplicity.

% and implementation for delegator objects

 

a_delegator::operation(String3),

String3 == 'delegate implementation'

 

=={{header|Objective-C}}==

{{works with|Cocoa}}

{{works with|GNUstep}}

 

@interface Delegator : NSObject {

 

return 0;

 

Objective-C 2.0, modern runtime, Automatic Reference Counting, Autosynthesize (LLVM 4.0+)

{{works with|Cocoa}}

 

 

// Formal protocol for the delegate

}

return 0;

 

=={{header|Oforth}}==

Object Class new: Delegate2

Object Class new: Delegator(delegate)

@delegate respondTo(#thing) ifTrue: [ @delegate thing return ]

Usage :

 

Default implementation

 

Default implementation

 

 

=={{header|ooRexx}}==

delegator = .delegator~new -- no delegate

say delegator~operation

nomethod:

return "default implementation"

 

=={{header|OxygenBasic}}==

class DelegateA 'not implmenting thing()

'==============

print dgr.thing 'result "not using Delegate"

print dg.thing 'result "Delegate Implementation"

 

=={{header|Oz}}==

{{trans|Python}}

class Delegator from BaseObject

attr

 

{A set({New Delegate noop})}

 

=={{header|Pascal}}==

=={{header|Perl}}==

{{trans|Python}}

 

package Delegator;

$a->{delegate} = Delegate->new;

$a->operation eq 'delegate implementation' or die;

 

Using Moose.

 

use 5.010_000;

 

$delegator->operation eq 'delegate implementation' or die;

 

 

 

 

 

 

 

 

 

 

 

 

=={{header|PHP}}==

{{trans|Python}}

function __construct() {

$this->delegate = NULL ;

 

$a->delegate = new Delegate() ;

 

=={{header|PicoLisp}}==

# delegate

 

# With delegate that implements 'thing>'

(put A 'delegate (new '(+Delegate) "delegate implementation"))

Output:

<pre>"default implementation"

 

=={{header|Pop11}}==

define :class Delegator;

slot delegate = false;

;;; delegating to a freshly created Delegate

newDelegate() -> delegate(a);

 

=={{header|Python}}==

def __init__(self):

self.delegate = None

# With delegate that implements "thing"

a.delegate = Delegate()

 

=={{header|Racket}}==

follows the requirement of the task better.

 

;; Delegates. Tim Brown 2014-10-16

 

(send delegator-2 operation) => "delegate implementation"

(send (new delegator% [delegate thinging-delegate]) operation) => "delegate implementation"))

 

All the tests pass. Believe me.

 

=={{header|Ruby}}==

{{trans|Python}}

attr_accessor :delegate

def operation

a.delegate = Delegate.new

puts a.operation # prints "delegate implementation"

 

Using Forwardable lib

 

 

class Delegator; extend Forwardable

a = Delegator.new

puts a.delegated # prints "Delegate"

 

=={{header|Swift}}==

Allowing the delegate to be any type and taking advantage of dynamism of method lookup:

 

func thing() -> String

}

let d = Delegate()

a.delegate = d

 

 

Alternately, requiring the delegate to conform to a given protocol:

func thing() -> String

}

let d = Delegate()

a.delegate = d

 

=={{header|Tcl}}==

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

Uses [[Assertions#Tcl]]

 

oo::class create Delegate {

assert {[a operation] ne "default implementation"}

 

 

To code the <code>operation</code> method without relying on catching an exception, but strictly by using introspection:

if { [info exists delegate] &&

[info object isa object $delegate] &&

set result "default implementation"

}

 

=={{header|Vorpal}}==

Delegate objects can be an array of delegates or as a single delegate.

a.f = method(){

.x.print()

d.delegate = a

d.x = 7

 

The resulting output:

4

7

</pre>

 

=={{header|zkl}}==

{{trans|Scala}}

class Delegator{

}

a:= Delegator();

a.operation().println(); //--> "default implementation"

// With a delegate:

a.delegate = Delegate();

A second example

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())}

 

Logger.dst=Console;

Logger.log("this is a test 2"); //-->writes to Console

 

class B(Logger){ log("Hello from ",self,"'s constructor"); }

 

The base class B was constructed at startup,

 

 

{{omit From|Fortran}}

{{omit From|Maxima}}