Send an unknown method call: Difference between revisions

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Invoke an object method where the name of the method to be invoked can be generated at run time.

Cf

AutoHotkey

This object has 3 methods, and asks the user to name one to call. Instead of using Func(), one could use a class definition. <lang AHK>obj := {mA: Func("mA"), mB: Func("mB"), mC: Func("mC")} InputBox, methodToCall, , Which method should I call? obj[methodToCall].()

mA(){

MsgBox Method A

} mB(){

MsgBox Method B

} mC(){

MsgBox Method C

} </lang>

Bracmat

<lang Bracmat>(task=

 ( oracle
 =   (predicate="is made of green cheese")
     (generateTruth=.str$(!arg " " !(its.predicate) "."))
     (generateLie=.str$(!arg " " !(its.predicate) "!"))
 )

& new$oracle:?SourceOfKnowledge & put

 $ "You may ask the Source of Eternal Wisdom ONE thing.

Enter \"Truth\" or \"Lie\" on the next line and press the <Enter> key. " & whl

 ' ( get':?trueorlie:~Truth:~Lie
   & put$"Try again\n"
   )

& put$(str$("You want a " !trueorlie ". About what?" \n)) & get'(,STR):?something & (SourceOfKnowledge..str$(generate !trueorlie))$!something ); </lang>

Example:

{?} !task
You may ask the Source of Eternal Wisdom ONE thing.
Enter "Truth" or "Lie" on the next line and press the <Enter> key.
"Lie"
You want a Lie. About what?
The sea
{!} The sea is made of green cheese!

Caché ObjectScript

$METHOD executes a named instance method for a specified instance of a designated class.

<lang cos>Class Unknown.Example Extends %RegisteredObject {

Method Foo() { Write "This is foo", ! }

Method Bar() { Write "This is bar", ! }

}</lang>

Examples:

USER>Set obj=##class(Unknown.Example).%New()
USER>Do $Method(obj, "Foo")
This is foo
USER>Do $Method(obj, "Bar")
This is bar

Common Lisp

Unknown methods are called just like any other function. Find the method-naming symbol using INTERN then call it with FUNCALL.

<lang lisp>(funcall (intern "SOME-METHOD") my-object a few arguments)</lang>

E

This example goes well with the object named example in Respond to an unknown method call#E.

<lang e>for name in ["foo", "bar"] {

   E.call(example, name, [])

}</lang>

Go

<lang go>package main

import (

   "fmt"
   "reflect"

)

type example struct{}

// the method must be exported to be accessed through reflection. func (example) Foo() int {

   return 42

}

func main() {

   // create an object with a method
   var e example
   // get the method by name
   m := reflect.ValueOf(e).MethodByName("Foo")
   // call the method with no argments
   r := m.Call(nil)
   // interpret first return value as int
   fmt.Println(r[0].Int()) // => 42

}</lang>

Icon and Unicon

<lang Unicon>procedure main()

  x := foo()    # create object
  x.m1()        # static call of m1 method
  #  two examples where the method string can be dynamically constructed ...
  "foo_m1"(x)   # ... need to know class name and method name to construct name
  x.__m["m1"]   # ... general method (better)

end

class foo(a,b,c) # define object method m1(x) end end</lang>

For more information on this see Respond to an unknown method call.

Java

Using reflection <lang java>import java.lang.reflect.Method;

class Example {

 public int foo(int x) {
   return 42 + x;
 }

}

public class Main {

 public static void main(String[] args) throws Exception {
   Object example = new Example();
   String name = "foo";
   Class<?> clazz = example.getClass();
   Method meth = clazz.getMethod(name, int.class);
   Object result = meth.invoke(example, 5); // result is int wrapped in an object (Integer)
   System.out.println(result);        // prints "47"
 }

}</lang>

JavaScript

String literal "foo" may be replaced by any expression resulting in a string <lang javascript>example = new Object; example.foo = function(x) {

   return 42 + x;

};

name = "foo"; example[name](5) # => 47</lang>

Logtalk

For this task, we first define a simple object with a single method: <lang logtalk>

- object(foo).

:- public(bar/1). bar(42).

- end_object.

</lang>

Second, we define another object that asks the user for a message to be sent to the first object:

- object(query_foo).

:- public(query/0). query :- write('Message: '), read(Message), foo::Message. write('Reply: '), write(Message), nl.

- end_object.

</lang>

After compiling and loading both objects, we can try:

<lang text> | ?- query_foo::query. Message: bar(X). Reply: bar(42) </lang>

Lua

Don't forget to pass the object for methods! <lang lua>local example = { } function example:foo (x) return 42 + x end

local name = "foo" example[name](example, 5) --> 47</lang>

MATLAB / Octave

 funName = 'foo';   % generate function name
 feval (funNAME, ...)  % evaluation function with optional parameters

 funName = 'a=atan(pi)';   % generate function name
 eval (funName, 'printf(Error\n)')

</lang>

Objective-C

<lang objc>#import <Foundation/Foundation.h>

@interface Example : NSObject { } - (NSNumber *)foo; @end

@implementation Example - (NSNumber *)foo {

 return [NSNumber numberWithInt:42];

} @end

int main (int argc, const char *argv[]) {

 NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];

 id example = [[Example alloc] init];
 SEL selector = @selector(foo); // or = NSSelectorFromString(@"foo");
 NSLog(@"%@", [example performSelector:selector]);
 [example release];
 
 [pool release];
 return 0;

}</lang> The performSelector: ... methods can only be used with methods with 0 - 2 object arguments, and an object or void return type. For all other calls, one can create an NSInvocation object and invoke it, or directly call one of the objc_msgSend family of runtime functions.

PARI/GP

Perl

<lang perl>package Example; sub new {

   bless {}

} sub foo {

   my ($self, $x) = @_;
   return 42 + $x;

}

package main; my $name = "foo"; print Example->new->$name(5), "\n"; # prints "47"</lang>

Perl 6

Just for the fun of it, we'll mix in an anonymous role into an integer instead of defining a class. <lang perl6>my $object = 42 but role { method add-me($x) { self + $x } } my $name = 'add-me'; say $object."$name"(5); # 47</lang> The double quotes are required, by the way; without them the variable would be interpreted as a hard ref to a method.

PHP

<lang php><?php class Example {

 function foo($x) {
   return 42 + $x;
 }

}

$example = new Example();

$name = 'foo'; echo $example->$name(5), "\n"; // prints "47"

// alternately: echo call_user_func(array($example, $name), 5), "\n"; ?></lang>

PicoLisp

This can be done with the 'send' function. <lang PicoLisp>(send (expression) Obj arg1 arg2)</lang>

Pike

with [] instead of -> a string can be used to name a method: <lang Pike>string unknown = "format_nice"; object now = Calendar.now(); now[unknown]();</lang>

Python

String literal "foo" may be replaced by any expression resulting in a string <lang python>class Example(object):

    def foo(self, x):
            return 42 + x

name = "foo" getattr(Example(), name)(5) # => 47</lang>

Qi

<lang qi> (define foo -> 5)

(define execute-function

 Name -> (eval [(INTERN Name)]))

(execute-function "foo") </lang>

Racket

lang racket

(define greeter

 (new (class object% (super-new)
        (define/public (hello name)
          (displayln (~a "Hello " name "."))))))

normal method call

(send greeter hello "World")

sending an unknown method

(define unknown 'hello) (dynamic-send greeter unknown "World") </lang>

Ruby

You may replace :foo, :bar or "bar" with any expression that returns a Symbol or String.

<lang ruby>class Example

 def foo
   42
 end
 def bar(arg1, arg2, &block)
   block.call arg1, arg2
 end

end

symbol = :foo Example.new.send symbol # => 42 Example.new.send( :bar, 1, 2 ) { |x,y| x+y } # => 3 args = [1, 2] Example.new.send( "bar", *args ) { |x,y| x+y } # => 3</lang>

Object#send can also call protected and private methods, skipping the usual access checks. Ruby 1.9 adds Object#public_send, which only calls public methods.

Works with: Ruby version 1.9

<lang ruby>class Example

 private
 def privacy; "secret"; end
 public
 def publicity; "hi"; end

end

e = Example.new e.public_send :publicity # => "hi" e.public_send :privacy # raises NoMethodError e.send :privacy # => "secret"</lang>

Smalltalk

<lang smalltalk>Object subclass: #Example.

Example extend [

 foo: x [
   ^ 42 + x ] ].

symbol := 'foo:' asSymbol. " same as symbol := #foo: "

Example new perform: symbol with: 5. " returns 47 "</lang>

The perform:with:with: family of methods exist for methods with 0 - 2 (3 in GNU Smalltalk) arguments. For methods with more arguments, use perform:withArguments:, which takes an array of arguments.

Tcl

Method names are really just strings, i.e., ordinary values that can be produced by any mechanism: <lang tcl>package require Tcl 8.6 oo::class create Example {

   method foo {} {return 42}
   method 1 {s} {puts "fee$s"}
   method 2 {s} {puts "fie$s"}
   method 3 {s} {puts "foe$s"}
   method 4 {s} {puts "fum$s"}

} set eg [Example new] set mthd [format "%c%c%c" 102 111 111]; # A "foo" by any other means would smell as sweet puts [$eg $mthd] for {set i 1} {$i <= 4} {incr i} {

   $eg $i ...

}</lang> The above produces this output:

42
fee...
fie...
foe...
fum...