Send an unknown method call

Revision as of 17:01, 28 August 2011 by rosettacode>Kernigh (→‎{{header|Ruby}}: Show that Object#send can call private methods.)

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

Send an unknown method call is a draft programming task. It is not yet considered ready to be promoted as a complete task, for reasons that should be found in its talk page.
Cf

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>

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 withObject:nil]);
 [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.

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

<lang perl6>$object."$methname"(5)</lang>

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>

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>

Ruby

You may replace :foo, :bar or "foo" 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>

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...