Send an unknown method call

Send an unknown method call
You are encouraged to solve this task according to the task description, using any language you may know.

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

Cf

• Respond to an unknown method call.
• Runtime evaluation

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.

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
}
 

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
);
 

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.

Class Unknown.Example Extends %RegisteredObject
{
 
Method Foo()
{
	Write "This is foo", !
}
 
Method Bar()
{
	Write "This is bar", !
}
 
}

Examples:

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

E

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

for name in ["foo", "bar"] {
    E.call(example, name, [])
}

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
}

Icon and 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

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

Java

Using reflection

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"
  }
}

JavaScript

String literal "foo" may be replaced by any expression resulting in a string

example = new Object;
example.foo = function(x) {
    return 42 + x;
};
 
name = "foo";
example[name](5)      # => 47

Lua

Don't forget to pass the object for methods!

local example = { }
function example:foo (x) return 42 + x end
 
local name = "foo"
example[name](example, 5) --> 47

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'')')
 

Objective-C

#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;
}

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

foo()=5;
eval(Str("foo","()"))

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"

Perl 6

Just for the fun of it, we'll mix in an anonymous role into an integer instead of defining a class.

my $object = 42 but role { method add-me($x) { self + $x } }
my $name = 'add-me';
say $object."$name"(5);  # 47

The double quotes are required, by the way; without them the variable would be interpreted as a hard ref to a method.

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";
?>

PicoLisp

This can be done with the 'send' function.

(send (expression) Obj arg1 arg2)

Pike

with [] instead of -> a string can be used to name a method:

string unknown = "format_nice";
object now = Calendar.now();
now[unknown]();

Python

String literal "foo" may be replaced by any expression resulting in a string

class Example(object):
     def foo(self, x):
             return 42 + x
 
name = "foo"
getattr(Example(), name)(5)      # => 47

Qi

 
(define foo -> 5)
 
(define execute-function
  Name -> (eval [(INTERN Name)]))
 
(execute-function "foo")
 

Ruby

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

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

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

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"

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 "

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:

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 ...
}

The above produces this output:

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