Send an unknown method call

From Rosetta Code
Task
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

AutoHotkey[edit]

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[edit]

(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!

C#[edit]

using System;
 
class Example
{
public int foo(int x)
{
return 42 + x;
}
}
 
class Program
{
static void Main(string[] args)
{
var example = new Example();
var method = "foo";
 
var result = (int)example.GetType().GetMethod(method).Invoke(example, new object[]{ 5 });
Console.WriteLine("{0}(5) = {1}", method, result);
}
}
 
Output:
 foo(5) = 47

Caché ObjectScript[edit]

$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

Common Lisp[edit]

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

(funcall (intern "SOME-METHOD") my-object a few arguments)

Déjà Vu[edit]

local :object { :add @+ }
local :method :add
 
!. object! method 1 2
Output:
3

E[edit]

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, [])
}

Elena[edit]

#import extensions.
 
class Example
{
foo : x
= x + 42.
}
 
program =
[
var example := Example new.
var methodSignature := "foo".
 
var result := example::(Signature new &literal:methodSignature) eval:5.
 
console writeLine:methodSignature:"(":5:") = ":result.
].

Forth[edit]

Works with: Forth

Works with any ANS Forth

Needs the FMS-SI (single inheritance) library code located here: http://soton.mpeforth.com/flag/fms/index.html

include FMS-SI.f
include FMS-SILib.f
 
var x \ instantiate a class var object named x
 
: test
heap> string locals| s |
'!' s +: ':' s +: \ build the message "!:" into string s
42 x s @: evaluate \ retrieve the text from s and execute it
x p: ; \ lastly, send the p: message to x to print it
 
test \ => 42 ok
 

Go[edit]

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
}

Groovy[edit]

class Example {
def foo(value) {
"Invoked with '$value'"
}
}
 
def example = new Example()
def method = "foo"
def arg = "test value"
 
assert "Invoked with 'test value'" == example."$method"(arg)

Icon and Unicon[edit]

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.

Io[edit]

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

Example := Object clone
Example foo := method(x, 42+x)
 
name := "foo"
Example clone perform(name,5) println // prints "47"

J[edit]

Solution: There are multiple ways to evoke code at runtime. The most common is ". y (evaluate the code in the string y, producing a noun), but there's also 'name'~ (which will modify J's stack by replacing the two tokens 'name' and ~ with the named object) as well as x 128!:2 y (apply the verb described by x to the noun y).

There are other methods as well, e.g., @.,`:, and ^:, though these are designed to consume gerunds (pre-parsed ASTs) rather than strings (though, of course, a pre-processor can always be provided to convert strings into ASTs before feeding them to these operators).

Example:
   sum =: +/
prod =: */
count =: #
 
nameToDispatch =: 'sum' NB. pick a name already defined
 
". nameToDispatch,' 1 2 3'
6
nameToDispatch~ 1 2 3
6
nameToDispatch (128!:2) 1 2 3
6
 
nameToDispatch =: 'count' NB. pick another name
 
". nameToDispatch,' 1 2 3'
3
nameToDispatch~ 1 2 3
3
nameToDispatch (128!:2) 1 2 3
3

Java[edit]

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[edit]

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

Lasso[edit]

define mytype => type {
public foo() => {
return 'foo was called'
}
public bar() => {
return 'this time is was bar'
}
}
local(obj = mytype, methodname = tag('foo'), methodname2 = tag('bar'))
#obj->\#methodname->invoke
#obj->\#methodname2->invoke
Output:
foo was called
this time is was bar

Lingo[edit]

obj = script("MyClass").new()
-- ...
method = #foo
arg1 = 23
res = call(method, obj, arg1)

Logtalk[edit]

For this task, we first define a simple object with a single method:

:- object(foo).
 
:- public(bar/1).
bar(42).
 
:- end_object.
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.
After compiling and loading both objects, we can try:
| ?- query_foo::query.
Message: bar(X).
Reply: bar(42)

Lua[edit]

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

Mathematica[edit]

Creates a dialog box where one can type a function (Sin, Cos, Tan ...) and then a second dialog box for a value.

ToExpression[Input["function? E.g. Sin",]][Input["value? E.g. 0.4123"]]
Output:
Input: Sin
Input: 3.1415
Output: 0.0000926536


MATLAB / Octave[edit]

 
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[edit]

#import <Foundation/Foundation.h>
 
@interface Example : NSObject
- (NSNumber *)foo;
@end
 
@implementation Example
- (NSNumber *)foo {
return @42;
}
@end
 
int main (int argc, const char *argv[]) {
@autoreleasepool {
 
id example = [[Example alloc] init];
SEL selector = @selector(foo); // or = NSSelectorFromString(@"foo");
NSLog(@"%@", [example performSelector:selector]);
 
}
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.

Oforth[edit]

A method object can be retrieved from its name using asMethod.

16 "sqrt" asMethod perform

Others :

  asFuntion  : retrieve a function
  asClass    : retrieve a class
  asProperty : retrieve a property

A generic way to search a word into the dictionary in to use find method :

16 "sqrt" Word find perform

PARI/GP[edit]

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

Perl[edit]

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[edit]

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.

Phix[edit]

Not specifically anything to do with objects, but you can construct routine names at runtime:

procedure Hello()
 ?"Hello"
end procedure
 
string erm = "Hemmm"
for i=3 to 5 do
erm[i]+=-1+(i=5)*3
end for
 
call_proc(routine_id(erm),{})

PHP[edit]

<?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[edit]

This can be done with the 'send' function.

(send (expression) Obj arg1 arg2)

Pike[edit]

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

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

PowerShell[edit]

A random method using a random number:

 
$method = ([Math] | Get-Member -MemberType Method -Static | Where-Object {$_.Definition.Split(',').Count -eq 1} | Get-Random).Name
$number = (1..9 | Get-Random) / 10
$result = [Math]::$method($number)
$output = [PSCustomObject]@{
Method = $method
Number = $number
Result = $result
}
 
$output | Format-List
 
Output:
Method : Atan
Number : 0.5
Result : 0.463647609000806

Python[edit]

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[edit]

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

Racket[edit]

 
#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")
 

Ruby[edit]

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"

Scala[edit]

Library: Scala
class Example {
def foo(x: Int): Int = 42 + x
}
 
object Main extends App {
val example = new Example
 
val meth = example.getClass.getMethod("foo", classOf[Int])
 
assert(meth.invoke(example, 5.asInstanceOf[AnyRef]) == 47.asInstanceOf[AnyRef], "Not confirm expectation.")
println(s"Successfully completed without errors. [total ${scala.compat.Platform.currentTime - executionStart} ms]")
}

Sidef[edit]

class Example {
method foo(x) {
42 + x
}
}
 
var name = 'foo'
var obj = Example()
 
say obj.(name)(5) # prints: 47
say obj.method(name)(5) # =//=

Smalltalk[edit]

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[edit]

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...

zkl[edit]

name:="len"; "this is a test".resolve(name)() //-->14