Which programming languages allow default values for method parameters?

Question

I'm curious which languages allow you to do something like this:

method foo(String bar = "beh"){

}

If you call foo like this:

foo();

bar will be set to "beh", but if you call like this:

foo("baz");

bar will be set to "baz".

Answer 1

I know Python allows this, while C,C++ don't.

Answer 2

as of c# 4.0 you can now have default params. Finally!

Also C++, Ruby and VB

Answer 3

Ones I can think of

• C# 4.0
• C++
• VB.Net (all versions)
• VB6
• F# (members only)
• Powershell
• IDL
• Ruby

Answer 4

PHP:

function foo($var = "foo") {
    print $var;
}

foo(); // outputs "foo"
foo("bar"); // outputs "bar"

Python:

def myFun(var = "foo"):
    print var

Ruby:

def foo(var="foo")
    print var
end

Groovy:

def foo(var="foo") {
    print var
}

Answer 5

Delphi has allowed this since about version 5 - released in 1999

procedure foo(const bar: string = 'beh');
begin
...
end;

foo;
foo('baz');

Answer 6

Perl does with Method::Signatures.

Answer 7

Java has a workaround.

You can have the foo method with no parameters that calls the foo method with parameters setting the default value, like this:

void foo() {
   foo("beh");
}

void foo(String bar) {
   this.bar = bar;
}

Answer 8

Python:

def foo(bar = value):
    # This function can be invoked as foo() or foo(something).
    # In the former case, bar will have its default value.
    pass

Answer 9

Add to the list Realbasic (indeed Realbasic has almost every nice feature of every language I can think of, including introspection and sandboxed scripting).

Python. (But watch out for mutables per http://effbot.org/zone/default-values.htm )

And plenty of languages, including C, allow variable numbers of parameters which effectively lets you do the same thing.

In many modern scripting languages, including PHP, JavaScript, and Perl, a better idiom for handling such things is to allow an associative array or object as a parameter, and then assign defaults if needed.

e.g.

function foo( options ){
  if( options.something === undefined ){
    options.something = some_default_value;
  }
  ...
}

This eliminates the necessity of putting the defaultable values at the end of the list of parameters and remembering all the stuff you don't want to override.

As always -- use in moderation.

Answer 10

TCL provides this functionality

proc procName {{arg1 defaultValue} {arg2 anotherDefaultValue}} {
    # proc body
}

Answer 11

• almost all Lisps
• Ruby
• Python
• C++
• C#
• Visual Basic.NET
• Tcl
• Visual Basic
• Ioke
• Seph
• Cobra
• Nemerle
• Mirah
• Delphi
• Groovy
• PHP
• Fancy
• Scala

Answer 12

D:

void foo(int x, int y = 3)
{
   ...
}
...
foo(4);   // same as foo(4, 3);

Fantom:

class Person
{
  Int yearsToRetirement(Int retire := 65) { return retire - age }

  Int age
}

Answer 13

You can do it in PL/SQL.

Answer 14

Racket provides this, as well as keyword arguments:

(define (f x [y 0]) (+ x y))
(f 1) ; => 1
(f 10 20) ; => 30

(define (g x #:y [y 0]) (- x y))
(g 1) ; => 1
(g 10 #:y 20) ; => -10

They're described in the documentation.