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.
Task

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


Related tasks



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!

C# 

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

$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


Clojure 

(import '[java.util Date])
(import '[clojure.lang Reflector])

(def date1 (Date.))
(def date2 (Date.))
(def method "equals")

;; Two ways of invoking method "equals" on object date1
;; using date2 as argument

;; Way 1 - Using Reflector class
;; NOTE: The argument date2 is passed inside an array
(Reflector/invokeMethod date1 method (object-array [date2]))

;; Way 2 - Using eval
;; Eval runs any piece of valid Clojure code
;; So first we construct a piece of code to do what we want (where method name is inserted dynamically),
;; then we run the code using eval
(eval `(. date1 ~(symbol method) date2))

Common Lisp

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 

local :object { :add @+ }
local :method :add

!. object! method 1 2
Output:
3

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, [])
}

Ecstasy

Here's a simple example of a test module using its runtime type to search for methods by some name (specified on the the command line), grabbing the one by that name that requires no parameters, and dynamically invoking it: 

module test {
    @Inject Console console;

    void run(String[] args) {
        String name = args.empty ? "foo" : args[0];
        if (val mm := &this.actualType.multimethods.get(name),
            val m  := mm.methods.any(m -> m.ParamTypes.size == 0)) {
            m.invoke(this, Tuple:());
        } else {
            console.print($"No such 0-parameter method: {name.quoted()}");
        }
    }

    void foo() {
        console.print("this is the foo() method");
    }

    void bar() {
        console.print("this is the bar() method");
    }
}
Output:
x$ xec test foo
this is the foo() method
x$ xec test bar
this is the bar() method
x$ xec test baz
No such 0-parameter method: "baz"

Elena

ELENA 4.1 : 

import extensions;
 
class Example
{
    foo(x)
        = x + 42;
}
 
public program()
{
    var example := new Example();
    var methodSignature := "foo";
 
    var invoker := new MessageName(methodSignature);
    var result := invoker(example,5);
 
    console.printLine(methodSignature,"(",5,") = ",result)
}
Output:
foo(5) = 47

Factor

Factor's object model is such that objects themselves don't contain methods — generic words do. So there is nothing different about invoking an unknown method than invoking an unknown word in general. 

USING: accessors kernel math prettyprint sequences words ;
IN: rosetta-code.unknown-method-call

TUPLE: foo num ;
C: <foo> foo
GENERIC: add5 ( x -- y )
M: foo add5 num>> 5 + ;

42 <foo>              ! construct a foo
"add" "5" append      ! construct a word name
                      ! must specify vocab to look up a word
"rosetta-code.unknown-method-call"
lookup-word execute . ! 47

Forth

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

\ Use a standard Forth string and evaluate it.
\ This is equivalent to sending the !: message to object x
42 x  s" !:"  evaluate  

x p: 42     \ send the print message ( p: ) to x to verify the contents

FreeBASIC 

Type Example
    foo As Integer Ptr
    Declare Constructor (x As Integer)
End Type

Constructor Example(x As Integer)
    This.foo = New Integer
    *This.foo = 42 + x
End Constructor

Dim As Example result = 5
Print *result.foo

Sleep
Output:
 47

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
}

Groovy 

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 

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

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

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

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

Julia

Works with: Julia version 0.6
const functions = Dict{String,Function}(
    "foo" => x -> 42 + x,
    "bar" => x -> 42 * x)

@show functions["foo"](3)
@show functions["bar"](3)
Output:
(functions["foo"])(3) = 45
(functions["bar"])(3) = 126

Kotlin

When you try to compile the following program, it will appear to the compiler that the local variable 'c' is assigned but never used and a warning will be issued accordingly. You can get rid of this warning by compiling using the -nowarn flag. 

// Kotlin JS version 1.1.4-3

class C {
    fun foo() {
        println("foo called")
    }
}

fun main(args: Array<String>) {
    val c = C()
    val f = "c.foo"
    js(f)()  // invokes c.foo dynamically
}
Output:
foo called

Lasso 

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 

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

Logtalk

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

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 /Wolfram Language

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 

  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 @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

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 

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

Pascal

Works with FPC (tested with version 3.2.2).

In the simplest case, when the methods are procedures without parameters, it might look something like this (note that these methods are currently required to have PUBLISHED visibility): 

program Test;
{$mode objfpc}{$h+}
uses
  SysUtils;

type
  TProc = procedure of object;

{$push}{$m+}
  TMyObj = class
  strict private
    FName: string;
  public
    constructor Create(const aName: string);
    property Name: string read FName;
  published
    procedure Foo;
    procedure Bar;
  end;
{$pop}

constructor TMyObj.Create(const aName: string);
begin
  FName := aName;
end;

procedure TMyObj.Foo;
begin
  WriteLn(Format('This is %s.Foo()', [Name]));
end;

procedure TMyObj.Bar;
begin
  WriteLn(Format('This is %s.Bar()', [Name]));
end;

procedure CallByName(o: TMyObj; const aName: string);
var
  m: TMethod;
begin
  m.Code := o.MethodAddress(aName);
  if m.Code <> nil then begin
    m.Data := o;
    TProc(m)();
  end else
    WriteLn(Format('Unknown method(%s)', [aName]));
end;

var
  o: TMyObj;

begin
  o := TMyObj.Create('Obj');
  CallByName(o, 'Bar');
  CallByName(o, 'Foo');
  CallByName(o, 'Baz');
  o.Free;
end.
Output:
This is Obj.Bar()
This is Obj.Foo()
Unknown method(Baz)

PascalABC.NET 

type MyClass = class
public  
  procedure Hello := Write('Hello');
end;

begin
  var obj := new MyClass;
  var mi := typeof(MyClass).GetMethod('Hello');
  mi.Invoke(obj,new object[0])
end.


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"

Phix

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

with javascript_semantics
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 

<?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";
?>

Picat

For functions use apply/n and for predicates call/n. The name of the function/predicate must be an atom and strings must be converted to atom, e.g. with to_atom/1. 

go =>
  println("Function: Use apply/n"),
  Fun = "fib",
  A = 10,
  % Convert F to an atom 
  println(apply(to_atom(Fun),A)),
  nl,

  println("Predicate: use call/n"),
  Pred = "pyth",
  call(Pred.to_atom,3,4,Z),
  println(z=Z),

  % Pred2 is an atom so it can be used directly with call/n.
  Pred2 = pyth,
  call(Pred.to_atom,13,14,Z2),
  println(z2=Z2),
   
  nl.

% A function
fib(1) = 1.
fib(2) = 1.
fib(N) = fib(N-1) + fib(N-2).

% A predicate
pyth(X,Y,Z) =>
  Z = X**2 + Y**2.
Output:
Function: Use apply/n
55

Predicate: use call/n
z = 25
z2 = 365

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]();

PowerShell

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

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")

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")

Raku

(formerly 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.

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"

Scala

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 

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 

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.


Swift

Generally speaking, pure Swift is a very statically typed language, and calling unknown methods is impossible. However, Swift provides a few ways in which instances of specially marked objects can receive unknown method calls.

Objective-C Compatibility Using @objc

The first case is used for interfacing with legacy Objective-C libraries. Objective-C is heavily dynamic with Smalltalk-style message passing. So Swift must be able to participate in this. 

import Foundation

class MyUglyClass: NSObject {
  @objc
  func myUglyFunction() {
    print("called myUglyFunction")
  }
}

let someObject: NSObject = MyUglyClass()

someObject.perform(NSSelectorFromString("myUglyFunction"))
Output:
called myUglyFunction

Dynamic Language Interop with @dynamicCallable and @dynamicMemberLookup

One of Swift's goals is to able to effectively bridge to dynamic languages such as Python and JavaScript. In order to facilitate more natural APIs, Swift provides the @dynamicCallable and @dynamicMemberLookup attributes which allow for runtime handling of method calls. 

@dynamicCallable
protocol FunDynamics {
  var parent: MyDynamicThing { get }

  func dynamicallyCall(withArguments args: [Int]) -> MyDynamicThing
  func dynamicallyCall(withKeywordArguments args: [String: Int]) -> MyDynamicThing
}

extension FunDynamics {
  func dynamicallyCall(withKeywordArguments args: [String: Int]) -> MyDynamicThing {
    if let add = args["adding"] {
      parent.n += add
    }

    if let sub = args["subtracting"] {
      parent.n -= sub
    }

    return parent
  }
}

@dynamicMemberLookup
class MyDynamicThing {
  var n: Int

  init(n: Int) {
    self.n = n
  }

  subscript(dynamicMember member: String) -> FunDynamics {
    switch member {
    case "subtract":
      return Subtracter(parent: self)
    case "add":
      return Adder(parent: self)
    case _:
      return Nuller(parent: self)
    }
  }
}

struct Nuller: FunDynamics {
  var parent: MyDynamicThing

  func dynamicallyCall(withArguments args: [Int]) -> MyDynamicThing { parent }
}

struct Subtracter: FunDynamics {
  var parent: MyDynamicThing

  func dynamicallyCall(withArguments args: [Int]) -> MyDynamicThing {
    switch args.count {
    case 1:
      parent.n -= args[0]
    case _:
      print("Unknown call")
    }

    return parent
  }
}

struct Adder: FunDynamics {
  var parent: MyDynamicThing

  func dynamicallyCall(withArguments arg: [Int]) -> MyDynamicThing {
   switch arg.count {
   case 1:
     parent.n += arg[0]
   case _:
     print("Unknown call")
   }

    return parent
  }
}

let thing =
  MyDynamicThing(n: 0)
    .add(20)
    .divide(2) // Unhandled call, do nothing
    .subtract(adding: 10, subtracting: 14)

print(thing.n)
Output:
16

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...

Wren 

import "meta" for Meta
 
class Test {
    construct new() {}
 
    foo() { System.print("Foo called.") }
 
    bar() { System.print("Bar called.") }
}

var test = Test.new()
for (method in ["foo", "bar"]) {
    Meta.eval("test.%(method)()")
}
Output:
Foo called.
Bar called.

zkl 

name:="len"; "this is a test".resolve(name)() //-->14
Retrieved from "https://rosettacode.org/wiki/Send_an_unknown_method_call?oldid=366050"