Named parameters: Difference between revisions

=={{header|11l}}==

 

R x*x + y*y + z*z

 

 

=={{header|Ada}}==

All callable entities (procedures, functions, entries) require named arguments. All of them can be called using either positional or keyed association of the actual arguments. The arguments supplied with default values can be omitted.

It can be equivalently called as:

Foo (1);

Foo (Arg_2 => 0.0, Arg_1 => 1);

 

=={{header|ALGOL 68}}==

{{trans|Lua}}

MODE OPTNAME = STRUCT(STRING name),

OPTSPECIES = STRUCT(STRING species),

OWNER=STRUCT(STRING first name, middle name, last name);

 

 

# due to the Yoneda ambiguity simple arguments must have an unique operator defined #

OP NAME = (STRING name)OPTNAME: (OPTNAME opt; name OF opt := name; opt),

SPECIES = (STRING species)OPTSPECIES: (OPTSPECIES opt; species OF opt := species; opt),

BREED = (STRING breed)OPTBREED: (OPTBREED opt; breed OF opt := breed; opt);

PROC print pet = (OPTIONS option)VOID: (

STRING name:="Rex", species:="Dinosaur", breed:="Tyrannosaurus"; # Defaults #

ESAC

OD;

);

print pet((NAME "Mike", SPECIES "Dog", BREED "Irish Setter", OWNER("Harry", "S.", "Truman")));

Output:

<pre>

</pre>

 

=={{header|AppleScript}}==

AppleScript does not implement default or optional parameters, but they can be simulated using records.

set {firstName, lastName} to {"?", "?"}

try

 

return firstName & ", " & lastName

Examples:

--> Returns: "John, Doe"

getName({lastName:"Doe"})

----

An easier way to achieve the above is by concatenating a record containing default values for the expected properties to the record actually passed. The result will contain the labels and values from both records, except that where the same label exists in both records, there'll only be one instance in the result and its value will be that from the first record:

 

set x to x & {firstName:"?", lastName:"?"}

return x's firstName & ", " & x's lastName

end getName

 

getName({lastName:"Doe"})

 

One of AppleScript's handler types has long been "handlers with labeled parameters". These haven't proved particularly popular as they have a limited set of AppleScript-defined labels, which can require some creativity when choosing one to make sense in the script narrative. However, labelled parameters can be given in any order in calls:

 

return firstName & ", " & lastName

end getName

 

getName beside "Doe" from "John"

 

However, it's also possible to define user labels, with the same flexibility of order, using a slightly different syntax:

 

return firstName & ", " & lastName

end getName

 

getName given lastName:"Doe", firstName:"John"

 

AppleScript-defined and user labels can be combined, but the AppleScript ones must be given first if used. The <tt>given</tt> syntax also has a neat feature whereby if the value to be passed is a boolean, the keyword <tt>with</tt> or <tt>without</tt> can be used instead in the call. In fact the compiler imposes this anyway when a boolean is hard-coded into the call:

 

if (comma) then

return firstName & ", " & lastName

--> "John, Doe"

getName without comma given lastName:"Doe", firstName:"John"

 

Since Mac OS X 10.10, it ''has'' been possible to make labelled parameters optional by defining default values for them in the handler declarations. But at least one parameter must be provided in any call:

 

 

on getName under category : "Misc: " given firstName:firstName : "?", lastName:lastName : "?", comma:comma : true

 

getName given lastName:"Doe"

 

=={{header|Applesoft BASIC}}==

Function definitions in Applesoft BASIC using the DEF FN statement can only have one parameter. Subroutines and functions with many parameters can be simulated using global variables which are effectively named parameters. Default or optional parameters can be simulated with a check in the subroutine.

 

110 IF LAST$ < > "" THEN PRINT LAST$;

120 IF FIRST$ < > "" THEN PRINT ", "FIRST$;

200 FIRST$ = ""

210 LAST$ = ""

 

<pre>]FIRST$ = "JOHN" : GOSUB 100"PRINT NAME

=={{header|Arturo}}==

 

print ["argument x:" x]

print ["attribute foo:" attr 'foo]

func .bar:"bar" 3

func .foo:123 .bar:124 4

 

{{out}}

 

 

 

 

 

attribute bar: 124</pre>

 

AutoHotkey doesn't have named parameters, but they can be simulated as follows.

ahk [http://www.autohotkey.com/forum/viewtopic.php?p=280499 discussion]

 

MyFunc( _overrides="" ) {

Static x=5, y=5, w=100, h=100, Count

Name:="AutoHotkey", Type:="Scripting", Text:="qwerty", Val:=True

Loop, Parse, _overrides,`,=, %A_Space% ; Override routine for Local/Static variables

A_Index & 1 ? (_:=A_LoopField) : (%_%:=A_LoopField)

Listvars

WinWaitClose, %A_ScriptFullPath%

 

=={{header|Bracmat}}==

In Bracmat, all functions have exactly one argument, called "arg". To split the argument and assign values to local variables, you always have to use pattern matching.

In this task, the pattern is just made a bit more complex than would have been the case without explicit parameter names in the argument.

= i x y z

. out$"Calling testproc"

& testproc$((z,4) (x,2) (y,3)) { order is not important }

& testproc$((i,1) (y,2) (z,3))

Output:

<pre>Calling testproc

{{works with|C99}}

 

 

// 1. Named parameters

FTest((FTest_args){ .y = 10, .z = 42 });

FT( .z = 47, .y = 10, .x = 42 );

// Default parameters

DFT();

DFT( .z = 99 );

// Default parameters with wrapper

DF2();

DF2( .z = 99 );

return 0;

 

As a bonus, default values for the parameters left unspecified can be either implicitly set to zero by the struct initializer, or supplied in a wrapper-macro definition. But this is not idiomatic C by any stretch.

Named parameters were added in C# 4.0. The examples below demonstrate how named parameters and optional parameters are a single concept in the language.

 

 

namespace NamedParams

}

}

 

Output:

You wrap the parameters in a class, and make the function a friend of the parameter class.

 

friend void foo(foo_params p);

public:

int required_param_;

int optional_x_;

float optional_z_;

 

Declare the function to take the parameter class as its only parameter.

 

 

Call the function using the parameter object constructor with the required parameters and chaining the optional parameters.

 

 

 

{{libheader|Boost}}

 

#include <boost/parameter/preprocessor.hpp>

#include <string>

tag, // part of the deep magic. If you use BOOST_PARAMETER_NAME you need to put "tag" here.

(required // names and types of all required parameters, parentheses are required.

(bar, (float))

)

(baz, (bool) , false)

(bonk, (std::string), "default value")

)

{

if (baz && (bar > 1.0)) return foo;

return bonk.size();

 

Once the definition is written, using it is easy, by name or position.

 

function_with_named_parameters(7, _bar = 3.14);

function_with_named_parameters( _bar = 0.0, _foo = 42);

function_with_named_parameters( _bar = 2.5, _bonk= "Hello", _foo = 9);

 

=={{header|Clojure}}==

Clojure doesn't have built-in support for named or keyword arguments, but you can use destructuring to achieve a similar effect.

 

(let [opts (merge {:bar 1 :baz 2} (apply hash-map opts))

{:keys [bar baz]} opts]

 

Clojure 1.2 supports destructuring of trailing arguments as a map:

 

 

You can also use <code>defnk</code> from <code>clojure.contrib.def</code>, which is a macro that works similarly.

 

(defnk foo [:bar 1 :baz 2]

 

Sample output for all variants:

=={{header|Common Lisp}}==

 

(princ last)

(when first

(princ ", ")

(princ first))

 

<code>&key</code> indicates that further parameters are named (keyword parameters); a bare symbol (e.g. <var>first</var>) has a default of NIL, whereas a list (e.g. <code>(<var>last</var> "?")</code>) gives the variable name and the default value (which is evaluated when the function is called, unlike Python).

 

?

CL-USER> (print-name :first "John")

Doe, John

CL-USER> (print-name :last "Doe")

 

In Common Lisp, the arguments to a function are always a simple list of values; the <code>&key</code> facility merely defines an interpretation of that list by the function: alternating keys and values. (As a result of this, mixing [[varargs]] (<code>&rest</code>) with named parameters is not recommended as it requires some additional means of distinguishing them. On the other hand, functions which pass their arguments on to other functions need not handle named arguments distinctly.)

 

{{omit from|D}}

 

=={{header|Dyalect}}==

Dyalect supports both named and optional parameters.

 

print("x=\(x), y=\(y), z=\(z), dsc=\(dsc)")

}

 

 

{{out}}

Since E supports arbitrary pattern matching (in the sense of [[Pattern Matching]] in parameter lists, a map-pattern can be used to provide named parameters, though the syntax is sufficiently noisy that this is not used casually.

 

if (last == null) {

print("?")

print(first)

}

 

(Note: In map literals and map patterns, “<code>=> <var>x</var></code>” is shorthand for “<code>"<var>x</var>" => <var>x</var></code>”.)

 

?, John

 

 

? printName(["first" => "John", "last" => "Doe"])

 

=={{header|Elixir}}==

The easiest and visually most appealing way to have named parameters is using a proplist as last parameter of the function.

 

def fun(bar: bar, baz: baz), do: IO.puts "#{bar}, #{baz}."

 

fun(bar: "bar", baz: "baz")

 

For this way to use them, order matters, as well as you can't define default values for arguments.

=={{header|Erlang}}==

At a guess "named parameters" are supposed to be used like proplists in Erlang.

Fun = fun( Proplists ) ->

Argument1 = proplists:get_value( argument1, Proplists, 1 ),

io:fwrite( "~p ~s~n", [Argument1, Kalle] )

end.

 

The function can now be called like these examples.

9 gustav

</pre>

 

=={{header|Factor}}==

Named parameters in Factor are as simple as changing the <code>:</code> word to <code>::</code> and using the variables defined in the stack effect declaration.

 

:: my-named-params ( a b -- c ) a b * ;

 

=={{header|Forth}}==

 

{{works with|Gforth}}

256 buffer: last-name

: is ( a "name" -- ) parse-name rot place ;

 

cr ." Hello, " first-name count type space last-name count type ." !" ;

 

require mini-oof2.fs

require string.fs

field: given-name

field: surname

end-class Person

 

cr ." Hiya, " given-name $. space surname $. ." !" ;

 

 

{{out}}<pre>Hello, Bob Hall!

Fortran accepts named parameter and optional parameter. Arguments are always named: if the name is omitted, the order used in the definition of the function / subroutine must be used.

 

integer, intent(in) :: arg1, arg2

integer, intent(out), optional :: arg3

! ...

 

integer :: r

call a_sub(1,2, r)

 

The presence of an optional argument can be tested with <tt>PRESENT</tt>; if optional arguments come before a non optional argument, the usage of the name of the argument is mandatory.

 

integer, intent(in), optional :: arg1

integer, intent(in) :: arg2

!...

 

call b_sub(arg2=1) ! ok

call b_sub(1, 2) ! ok: arg1 is 1, arg2 is 2

 

=={{header|Go}}==

 

Here's a simple example.

 

import (

t := myFunc(params{y: 2}) // only one field, others set to zero

fmt.Println("t =", t)

 

{{out}}

We can simulate named, but not moveable arguments, with nullary data constructors:

 

data Y = Y

data Point = Point Int Int deriving Show

createPointAt X x Y y = Point x y

 

 

We can also emulate named, moveable, optional arguments with record syntax:

 

defaultPoint = Point {x = 0, y = 0}

 

createPointAt :: Point -> Point

createPointAt = id

 

Though this is cumbersome without using template Haskell, as the call site must supply the defaults.

 

 

testproc("x:=",1,"y:=",2,"z:=",3)

testproc("x:=",3,"y:=",1,"z:=",2)

((variable(a[1:-2]) := get(A)) | # assign

runerr(205,a))) # . . problem

write(" x:=",x)

write(" y:=",y)

write(" z:=",z)

{{improve|Icon|there is currently a bug in Icon that causes assignments via variable("x") to fail for local and static variables. Remove this when this is fixed. The bug does not appear in Unicon.}}

 

J is similar to Perl in that all arguments to functions come in as separate elements in an array. But it is possible to emulate more complex calling conventions. For example, using the [http://www.jsoftware.com/svn/DanBron/trunk/environment/calling_convention.ijs calling convention J script], one could write:

 

myFunc['c:\file.txt' 906 'blue' fs]

NB. Commas, like other langs

myFunc['c:\file.txt', 906, 'blue' fs]

NB. Unspecified args are defaulted ("optional")

myFunc['c:\file.txt' fs]

NB. Can use named arguments, like eg VB

myFunc[color='blue' fs]

NB. Often values needn't be quoted

myFunc[color= blue fs]

NB. Combination of comma syntax and name=value

myFunc[max=906, color=blue fs]

NB. Spelling of names is flexible

myFunc[MAX=906, COLOR=blue fs]

NB. Order of names is flexible

myFunc[COLOR=blue, MAX=906 fs]

NB. Even the delimiters are flexible...

 

For further discussion, see the [http://www.jsoftware.com/pipermail/programming/2009-July/015571.html corresponding thread in the J Forums].

=={{header|Java}}==

Like C++, Java also does not support named parameters. Named parameters can however be simulated simply with the "Builder pattern". ([http://drdobbs.com/java/208403883?pgno=2 Joshua Bloch: Builder Pattern])

Follow the link for extra details about the 'NutritionFacts' class example.

 

=={{header|JavaScript}}==

JavaScript only has positional parameters, but named parameters can be emulated by passing an object with the appropriate properties:

// assign some defaults where the user's has not provided a value

opts = {}

 

example({grill: "lamb kebab", bar: 3.14});

===ECMAScript 2015 (ES6) variants===

example = // The member name in the object can either be the same as the parameter (as in bar, grill),

// or a different parameter name as in the case of member foo being assigned to parameter a here.

// foo is 0 , bar is 3.14 , and grill is lamb kebab

example({foo:null});

 

=={{header|jq}}==

 

For example, here is the jq analog of "print-name" defined in the Common Lisp section above. Here we format the full name and return it as a string:

def formatName(obj):

({ "name": "?"} + obj) as $obj # the default default value is null

| ($obj|.name) as $name

| if ($first == null) then $name

else $name + ", " + $first

end;

 

Here are examples of how the function can be invoked:

formatName({"first": "George", "name": "Eliot"})

 

 

formatName({})

 

=={{header|Julia}}==

Julia supports arbitrary named keyword arguments, which are listed (with their default values) after a <code>;</code> in the function definition:

 

 

println(ul, ho^(length(string) + 2padding), ur, "\n",

ve, " "^padding, string," "^padding, ve, "\n",

dl, ho^(length(string) + 2padding), dr)

 

{{Out}}

 

=={{header|Kotlin}}==

 

fun someFunction(first: String, second: Int = 2, third: Double) {

fun main(args: Array<String>) {

// using positional parameters

 

// using named parameters

 

// using first and third parameters in reverse

 

{{out}}

 

=={{header|Lasso}}==

-first::integer, // with no default value the param is required

-second::integer,

-first = 54,

-delimiter = '#'

-> 54:45

 

=={{header|Lingo}}==

Lingo does not support named function parameters. But this can be simulated by using a single property list (hash) with named properties as function argument. You can also create functions that support both calling methods, like e.g. this function that accepts either 3 integers or a single property list with such named properties:

on foo (arg1, arg2, arg3)

if ilk(arg1)=#propList then

-- "arg1="

-- "arg2="

 

=={{header|Lua}}==

function CreatePet(options)

local name=options.name

CreatePet{name='Rex',species='Dog',breed='Irish Setter'}

--position does not matter here.

 

=={{header|M2000 Interpreter}}==

Passing optionals in modules may cause problems if we have values in stack, so we can use Stack New {] to open an empty current stack (the old one is hidden until exit from that block), or using ? as "use standard value".

 

module namedparam (x as decimal=10, y as integer=50) {

Print type$(x), x

}

namedparam %x=1, %y=1

 

=={{header|Maple}}==

print (a*(c+b));

end proc:

3

f(2, b = 5, c = 3);#b and c can be put in any order

 

fn[x_,y_,OptionsPattern[]]:=If[OptionValue[Add]==True,x+y+OptionValue[Offset],{x,y,OptionValue[Offset]}]

fn[3,4,{Add->True,Offset->2}]

 

=={{header|MATLAB}} / {{header|Octave}}==

Named parameters are not natively supported. However, the following code can be used to implement them.

 

for k= 1:2:length(varargin);

switch (varargin{k})

case {'param2'}

param2 = varargin{k+1};

 

param1: a1

param2: b2

param1: a1

param2: b2</pre>

Much like [[Ada]], Modula-3 allows either positional or keyed association of actual parameters. Defaults can also be ignored.

 

It can be equivalently called as:

Foo(1);

Foo(Arg2 := 0.0, Arg1 := 1);

 

=={{header|Nemerle}}==

 

Foo(word = "Bird", number = 3) // an argument with a default value can be omitted from function call

Foo(3, option = false, word = "Bird") // unnamed arguments must be in same order as function definition and precede named arguments

 

=={{header|Nim}}==

In Nim, a regular parameter of a procedure can be used as either a positional or a named parameter.

 

 

echo subtract(5, 3) # used as positional parameters

 

Parameters can be made optional by providing a default argument.

=={{header|Objective-C}}==

Objective-C, like Smalltalk, has a method call syntax that is visually identical to named arguments, but they are not optional and may not be reordered. (Optional arguments may be simulated by defining multiple methods with the same leading name part.)

// Omitted ...

}

- (double) hypotenuseOfX: (double)x andY: (double)y andZ: (double)z;

 

 

- (double) hypotenuseOfX: (double)x andY: (double)y {

}

 

Note in the example above that the name of the method, the ''selector''; is actually “<code>hypotenuseOfX:andY:</code>”.

 

=={{header|OCaml}}==

You can make a named argument (called ''labels'' in OCaml) by putting a tilde (~) before the name:

val foo : arg1:int -> arg2:int -> int = <fun>

# let foo ~arg1:x ~arg2:y = x + y;; (* you can also use different variable names internally if you want *)

val foo : arg1:int -> arg2:int -> int = <fun>

# foo ~arg2:17 ~arg1:42;;

 

Named arguments can be re-ordered, but two arguments of the same label cannot be re-ordered relative to each other.

=={{header|Oz}}==

For <b>methods</b>, Oz does support named parameters with default values. The named parameters can be freely reordered.

class Foo

meth init skip end

{O bar(1 named1:2 named2:3 namedWithDefault:4)} %% ok

{O bar(1 named2:2 named1:3)} %% ok

 

For <b>procedures</b> only positional parameters are supported. However, you can emulate named parameters by using records:

declare

proc {Foo PP Other=unit(named1:N1 named2:N2 ...)}

{Foo 1 unit(named1:2 named2:3 namedWithDefault:4)}

{Foo 1 unit(named2:2 named1:3)}

 

The procedure Foo is defined with pattern matching in the argument list. The ellipsis means that additional record fields are allowed. To access optional record fields, we have to explicitly try to select a field and provide a default value in case it is missing ("CondSelect").

 

=={{header|Perl}}==

Perl has no non-experimental formal parameters. Instead, Perl subroutines access all of their arguments through the special array <code>@_</code>. You can easily implement named arguments by making your function interpret <code>@_</code> (or part of it) as a hash.

 

my %h = @_;

# Print every argument and its value.

# Otherwise, say that it's off.

print "Safe mode ", ($h{safe} ? 'on' : 'off'), ".\n";

The semantics of calling such a function follow directly from the semantics of using a hash. For instance, if you provide multiple values for the same named argument, only the last one will be used. An example call:

 

verbosity => 3,

password => 'foobie blech',

'42' => 'answer',

password => 'joshua'

Its output:

 

Safe mode off.</pre>

 

{

my ($params_ref, $name) = @_;

my @known_params = qw(attendees event food time);

 

$name // 'Anonymous';

 

ucfirst $_,

? join ', ', @{ $params{$_} }

: $params{$_};

 

event(

# create a reference to an anonymous hash

attendees => ['Bob', 'Betty', 'George', 'Bertha'],

},

"Joe Schmoe"

<pre>

Joe Schmoe called event() with the following named parameters:

=={{header|Phix}}==

{{libheader|Phix/basics}}

 

 

=={{header|PHP}}==

PHP doesn't support named parameters but you can simulate the behavior with PHP arrays.

$args += ["gbv" => 2,

"motor" => "away",

}

 

Output:

<pre>10 men running away from the cia</pre>

to establish bindings to passed names.

===Passing symbol-value pairs===

(bind (rest) # Bind symbols in CARs to values in CDRs

(println 'Bar 'is Bar)

(println 'Mumble 'is Mumble) ) )

 

===Passing a name list followed by values===

(bind (next) # Save all symbols in first argument

(mapc set (arg) (rest)) # then bind them to remaining arguments

(println 'Mumble 'is Mumble) ) )

 

Output in both cases:

<pre>Bar is 123

===Positional parameters===

When writing a function and not stating any parameters explicitly, such as the following function

Write-Host Argument 1 is $args[0]

the only option are positional parameters using the <code>$args</code> array.

===Named parameters===

Stating any number of parameters directly in the function definition, such as

Write-Host "Some argument: $SomeArgument"

Write-Host "Another argument: $AnotherArgument"

Write-Host "Third argument: $ThirdArgument"

will cause them to be named automatically which enables the caller to state the arguments in any order. The syntax follows the convention used with cmdlets as well:

<pre>PS> Test -ThirdArgument foo -AnotherArgument bar -SomeArgument baz

===Switch parameters===

Functions can have so-called ''switch parameters'' which are always boolean and either present or not. There is no need to give a value for them.

Write-Host Switched $(if ($on) { "on" } else { "off" })

When calling a function with such a parameter the switch is simply given directly (which sets its value to ''true'') or omitted (which causes it to evaluate to ''false''):

<pre>PS> SwitchTest

===Optional parameters and default values===

Usually all parameters can be omitted. In the case of switch parameters this will cause them to assume the value ''false'', for normal parameters they will have the value <code>$null</code>. This is not always the desired value, though. Default values can be given too:

Write-Host Hello, $Name!

If the <code>Name</code> argument is omitted now, its value will be <code>"Nobody"</code> instead of <code>$null</code>:

<pre>PS> Greeting

=={{header|Prolog}}==

{{works with|SWI Prolog}}

 

main :-

member(A,C),

named_args(B,C).

 

=={{header|Python}}==

In Python, a regular parameter of a function can be used as ''either a positional or a named'' parameter. The variable name that you use for the parameter when you declare the function becomes the "name" for the parameter, should you use it as a named parameter. When you call a function, you use the "name = value" syntax to provide the argument to a named parameter. The named arguments must come after all the positional arguments.

 

return x - y

 

subtract(5, 3) # used as positional parameters; evaluates to 2

 

Parameters can be made optional by providing a default argument, as described in the [[optional parameters]] article.

====Function Definition Parameters====

Function definitions in Python allow for the following ''parameter'' types:

* An optional ''positional parameter'' which is an identifier preceded by <code>"*"</code>.

* And an optional ''keyword parameter'' which is an identifier preceded by <code>"**"</code>.

* All positional arguments must appear before any keyword argument.

* ''Keyword arguments'' of the form <code>parameter_name "=" value</code> will map the value to the <code>defparameter</code> in the definition of the same name.

* If the function ''definition'' includes a ''positional parameter'', then if the assignment of ''positional arguments'' and ''sequence arguments'' in the ''call'' gives more values than the <code>defparameters</code> of the definition, then these extra arguments are assembled, in order, into a tuple that is assigned to the <code>posparameter</code> of the definition.

* If the function ''definition'' includes a ''keyword parameter'', then if the parameter name of any ''keyword arguments'' and ''mapping arguments'' in the ''call'' is unknown in the <code>defparameters</code> of the function definition, then these extra keyword/value pairs are assembled into a dict that is assigned to the <code>keyparameter</code> of the definition.

* Any ''default parameter'' of the function ''definition'' that is still un-assigned will cause a <code>TypeError</code> exception to be raised.

* In addition, multiple mappings to any parameter will raise a <code>TypeError</code> exception. (This includes multiple mappings into a <code>keyparameter</code> or keyword arguments clashing with positional/sequence arguments).

 

====Examples====

>>> def show_args(defparam1, defparam2 = 'default value', *posparam, **keyparam):

"Straight-forward function to show its arguments"

print (" <None>")

 

>>> show_args('POSITIONAL', 'ARGUMENTS')

Default Parameters:

Keyword Arguments (by sorted key name):

<None>

'EXTRA', 'POSITIONAL', 'ARGUMENTS')

Default Parameters:

Keyword Arguments (by sorted key name):

<None>

kwa1='EXTRA', kwa2='KEYWORD', kwa3='ARGUMENTS')

Default Parameters:

keyword argument: kwa2 is: KEYWORD

keyword argument: kwa3 is: ARGUMENTS

kwa1='EXTRA', kwa2='KEYWORD', kwa3='ARGUMENTS')

Default Parameters:

keyword argument: kwa3 is: ARGUMENTS

>>> # But note:

'EXTRA', 'POSITIONAL', 'ARGUMENTS')

SyntaxError: non-keyword arg after keyword arg

 

=={{header|R}}==

R parameters are all named; arguments can be passed either positionally or with explicit naming. The named arguments are matched to their parameters first, then the unnamed arguments fill in remaining slots. A parameter whose name begins with a period will not be matched to unnamed arguments. R allows abbreviated names to be used as long as they match uniquely to an argument.

 

numerator / denominator

}

divide(den=3, num=2) # 0.66

divide(den=3, 2) # 0.66

 

=={{header|Racket}}==

Racket has built-in keyword and optional arguments:

 

#lang racket

 

(define (pizza sauce

;; mandatory keyword argument

;; optional keyword argument with default

#:type [type "deep dish"])

(pizza "tomato" #:topping "onion")

(pizza #:topping "onion" "garlic" #:type "pan")

 

=={{header|Raku}}==

Raku's support for optional parameters is much like Python's. Consider this declaration:

 

...

 

In the above signature:

So, if we defined the function like this:

 

say "$a $b $c $d";

say join ' ', @e;

funkshun

'Alfa', k1 => 'v1', c => 'Charlie', 'Bravo', 'e1',

 

would print this:

=={{header|REXX}}==

===version 1===

/*┌────────────────────────────────────────────────────────────────────┐

│ The syntax of: xxx = func1(parmName2=arg2, parmName1=arg1) │

 

return 'the final meaning of life, or 42 --- whichever is appropriate.'

===version 2===

* 01.07.2014 Walter Pachl

* Argument values must not start with 'arg'

Say 'p.'i'='p.i

End

{{Out}}

<pre>p.1=2

{{trans|Tcl}}

{{works with|Ruby|2.0}}

puts "foo is #{foo}, bar is #{bar}, and grill is #{grill}"

end

 

# Note that :foo is omitted and :grill precedes :bar

 

Ruby 1.9 can fake the effect with a Hash. If a caller passes <code>name: value</code> pairs, Ruby makes a Hash, and the called method sees this Hash in its last argument. To complete the effect, the method may declare an optional last argument that defaults to an empty Hash <code>{}</code>. In this version, <code>example(typo: 4)</code> causes no error.

{{works with|Ruby|1.9}}

 

# Hash#merge raises TypeError if _opts_ is not a Hash.

# Nothing checks if _opts_ contains unknown keys.

end

 

 

{{omit from|Rust}}

Scala 2.8 utilizes named parameters and default values:

 

def add(x: Int, y: Int = 1) = x + y

 

scala> add(5)

6

scala> add(y=10, x=4)

14

 

=={{header|Scheme}}==

(define (keyarg-parser argdefs args kont)

(apply kont

(display first)))

(newline))))

 

=> (print-name)

?

=>(print-name 'last "Doe")

Doe

 

=={{header|Sidef}}==

say "foo is #{foo}, bar is #{bar}, and grill is #{grill}";

}

 

# Note that :foo is omitted and :grill precedes :bar

{{out}}

<pre>foo is 0, bar is 3.14, and grill is lamb kebab</pre>

{{works with|GNU Smalltalk}}

 

"..."

initWithArray: anArray [ "single argument" ]

"two args; these two methods in usage resemble

a named argument, with optional andString argument"

]

"..."

 

=={{header|Standard ML}}==

This example uses Standard ML "fields".

 

 

To call the procedure ''example'', use:

However, this does not support optional parameters. To emulate them, we can process a parameter list:

 

fun args xs =

map (fn (A x) => a := x | (B x) => b := x | (C x) => c := x) xs;

(!a, !b, !c)

To process the argument list and call ''example'', use:

 

=={{header|Suneido}}==

Suneido can handle named and unnamed parameters. When using a combination, unnamed parameters must come before named ones and must be in the correct order. Named parameters can be in any order. Named parameters are given a default value so they are not mandatory.

test = function (one, two, three = '', four = '', five = '')

{

', four: ' $ four $ ', five: ' $ five)

}

test('1', '2', five: '5', three: '3')

Output:

 

=={{header|Swift}}==

Each function parameter has both an argument label and a parameter name. The argument label is used when calling the function; each argument is written in the function call with its argument label before it. The parameter name is used in the implementation of the function. By default, parameters use their parameter name as their argument label.

 

return "Hello \(person)! Glad you could visit from \(hometown)."

}

You write an argument label before the parameter name, separated by a space:

return "Hello \(person)! Glad you could visit from \(hometown)."

}

 

If you don’t want an argument label for a parameter, write an underscore (_) instead of an explicit argument label for that parameter.

If a parameter has an argument label, the argument must be labeled when you call the function.

return "Hello \(person)! Glad you could visit from \(hometown)."

}

 

You can define a default value for any parameter in a function by assigning a value to the parameter after that parameter’s type. If a default value is defined, you can omit that parameter when calling the function.

return "Hello \(person)! Glad you could visit from \(hometown)."

}

 

=={{header|Tcl}}==

The simplest way of passing named parameters is to use the Tcl language's strong support for [[Varargs#Tcl|variadic commands]] together with its arrays. By convention (originally from [[Tk]]) the named parameters names start with a hyphen (“<tt>-</tt>”) and are called options.

# Set the defaults

array set opts {-foo 0 -bar 1 -grill "hamburger"}

# Note that -foo is omitted and -grill precedes -bar

example -grill "lamb kebab" -bar 3.14

More complex option parsing is possible, e.g., with the <tt>opt</tt> package (of which only a small fraction of the functionality is shown here). This package also allows you to specify type constraints, though that is usually not necessary, and will generate a standard help message that can be obtained with the <tt>-help</tt> option:

tcl::OptProc example {

{-foo -int 0 "The number of foos"}

# -foo int (0) The number of foos

# -bar float (1.0) How much bar-ness

 

According to [http://wiki.tcl.tk/1730 wiki.tcl.tk discussions], '''::tcl::OptProc is deprecated.'''

The recommended replacement is [http://tcllib.sourceforge.net/doc/cmdline.html cmdline] in [http://tcllib.sourceforge.net/doc/index.html tcllib]. "This is probably the most standard and widely-used of these packages."

 

=={{header|VBA}}==

Public Function timedelta(Optional weeks As Integer = 0, Optional days As Integer = 0, _

Optional hours As Integer = 0, Optional minutes As Integer = 0, Optional seconds As Integer = 0, _

'-- timedelta(0,hours:=15,3) '-- illegal (it is not clear whether you meant days:=3 or minutes:=3)

'VBA expects a named parameter for 3

 

=={{header|Visual Basic}}==

Sub whatever(foo As Long, bar As Integer, baz As Byte, qux As String)

'...

Sub crap()

whatever bar:=1, baz:=2, foo:=-1, qux:="Why is ev'rybody always pickin' on me?"

 

=={{header|Wren}}==

Wren doesn't support named parameters as such though they can be simulated using a map.

if (!(name is Map && name["first"] != null && name["last"] != null)) {

Fiber.abort("Argument must be a map with keys \"first\" and \"last\"")

printName.call({"first": "Abraham", "last": "Lincoln"}) // normal order

printName.call({"last": "Trump", "first": "Donald"}) // reverse order

 

{{out}}

=={{header|XSLT}}==

XSLT only allows specification of template parameters by name, not position.

<xsl:param name="title"/>

...

{{omit from|Axe}}

{{omit from|BASIC}}

{{omit from|bc}}

{{omit from|dc}}

{{omit from|GUISS}}

{{omit from|Joy}}

{{omit from|TI-89 BASIC}}

{{omit from|UNIX Shell}}

{{omit from|zkl}}

{{omit from|ZX Spectrum Basic}}