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".

I think this might be a candidate for communiwikification... — David Z
– David Z, Commented Oct 7, 2010 at 20:05
are you asking for an exhaustive list in one answer or just everyone give their favorite example?? — Scott Evernden
– Scott Evernden, Commented Oct 7, 2010 at 20:08
What I would love would be a single answer that names all languages that do allow this with syntax examples. In retrospect, yes this would be a great candidate for wikification. — cmcculloh
– cmcculloh, Commented Oct 7, 2010 at 20:14

Jörg W Mittag · Accepted Answer · 2010-10-07 19:53:54Z

11

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

answered Oct 7, 2010 at 19:53

Jörg W Mittag

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1 Comment

sepp2k Over a year ago

OCaml has default arguments as well (for named arguments).

NullUserException · Accepted Answer · 2010-10-07 20:00:50Z

8

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
}

edited Oct 7, 2010 at 20:00

answered Oct 7, 2010 at 19:46

NullUserException

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2 Comments

cmcculloh Over a year ago

This is exactly the kind of answer I'm looking for. The language and then an example in that langauge.

NullUserException Over a year ago

@Alaor Because this is not by any means an exhaustive list

JaredPar · Accepted Answer · 2010-10-07 19:49:49Z

8

Ones I can think of

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

edited Oct 7, 2010 at 19:49

answered Oct 7, 2010 at 19:44

JaredPar

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Comments

2 revs · Accepted Answer · 2010-10-13 04:34:07Z

3

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.

edited Oct 13, 2010 at 4:34

community wiki

2 revs
Sam Tobin-Hochstadt

Comments

Gerry Coll · Accepted Answer · 2010-10-07 19:46:36Z

2

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

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

foo;
foo('baz');

answered Oct 7, 2010 at 19:46

Gerry Coll

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CanSpice · Accepted Answer · 2010-10-07 19:48:39Z

2

Perl does with Method::Signatures.

answered Oct 7, 2010 at 19:48

CanSpice

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salezica · Accepted Answer · 2010-10-07 19:50:35Z

2

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

answered Oct 7, 2010 at 19:50

salezica

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Comments

Chris Kooken · Accepted Answer · 2010-10-07 19:51:18Z

2

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

Also C++, Ruby and VB

edited Oct 7, 2010 at 19:51

answered Oct 7, 2010 at 19:44

Chris Kooken

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SingleNegationElimination · Accepted Answer · 2010-10-07 19:53:45Z

2

TCL provides this functionality

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

answered Oct 7, 2010 at 19:53

SingleNegationElimination

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Corbin March · Accepted Answer · 2010-10-07 19:58:02Z

1

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
}

answered Oct 7, 2010 at 19:58

Corbin March

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pablosaraiva · Accepted Answer · 2010-10-07 19:49:49Z

0

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;
}

answered Oct 7, 2010 at 19:49

pablosaraiva

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4 Comments

JaredPar Over a year ago

The name for this is method overloading.

pablosaraiva Over a year ago

Sure, but since he didn't asked about method overloading, but about method default parameters values, method overloading is a workaround.

bobince Over a year ago

And it's super-fun writing eight overloaded methods to reproduce three defaultable arguments, eh. Especially when Policy demands each needs to have its own lengthy XML javadoc. aaargh.

pablosaraiva Over a year ago

I'm not defending Java here. I'm just posting the workaround. And it's not necessary to write 8 methods for 3 default arguments, only 4.

podperson · Accepted Answer · 2010-10-07 19:52:06Z

0

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.

answered Oct 7, 2010 at 19:52

podperson

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3 Comments

NullUserException Over a year ago

"allow an associative array or object as a parameter" Unless you have a large list of arguments with no consistent usage frequency, this is a horrible idea.

rmeador Over a year ago

IIRC, REALbasic started out life as a Visual Basic clone for the Mac. Given this pedigree, I'll respectfully disagree with your assertion that it "has almost every nice feature of every language". I won't downvote you, though.

podperson Over a year ago

@NullUserException: if you don't have arbitrary lists of one kind of argument, why is it a horrible idea? It's a simple tradeoff of performance vs. flexibility/robustness/expandability. When coding libraries I frequently find myself regretting not having chosen this approach. @meador RB was never a VB "clone". It was a completely OO language from day one (before VB.NET) which tried to allow relatively easy porting of VB projects. RB has never had the ugliness of VB.

Nils Weinander · Accepted Answer · 2010-10-07 20:10:35Z

0

You can do it in PL/SQL.

answered Oct 7, 2010 at 20:10

Nils Weinander

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Comments

highBandWidth · Accepted Answer · 2010-10-07 19:43:39Z

-2

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

answered Oct 7, 2010 at 19:43

highBandWidth

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