Hướng dẫn dùng define extracts trong PHP

Information may be passed to functions via the argument list, which is a comma-delimited list of expressions. The arguments are evaluated from left to right, before the function is actually called (eager evaluation).

PHP supports passing arguments by value (the default), passing by reference, and default argument values. Variable-length argument lists and Named Arguments are also supported.

Example #1 Passing arrays to functions

function takes_array($input)
{
    echo "$input[0] + $input[1] = ", $input[0]+$input[1];
}
?>

As of PHP 8.0.0, the list of function arguments may include a trailing comma, which will be ignored. That is particularly useful in cases where the list of arguments is long or contains long variable names, making it convenient to list arguments vertically.

Example #2 Function Argument List with trailing Comma

function takes_many_args(
    $first_arg,
    $second_arg,
    $a_very_long_argument_name,
    $arg_with_default = 5,
    $again = 'a default string', // This trailing comma was not permitted before 8.0.0.
)
{
    // ...
}
?>

Passing arguments by reference

By default, function arguments are passed by value (so that if the value of the argument within the function is changed, it does not get changed outside of the function). To allow a function to modify its arguments, they must be passed by reference.

To have an argument to a function always passed by reference, prepend an ampersand (&) to the argument name in the function definition:

Example #3 Passing function parameters by reference

function add_some_extra(&$string)
{
    $string .= 'and something extra.';
}
$str = 'This is a string, ';
add_some_extra($str);
echo $str;    // outputs 'This is a string, and something extra.'
?>

It is an error to pass a value as argument which is supposed to be passed by reference.

Default argument values

A function may define default values for arguments using syntax similar to assigning a variable. The default is used only when the parameter is not specified; in particular, note that passing null does not assign the default value.

Example #4 Use of default parameters in functions

function makecoffee($type = "cappuccino")
{
    return "Making a cup of $type.\n";
}
echo makecoffee();
echo makecoffee(null);
echo makecoffee("espresso");
?>

The above example will output:

Making a cup of cappuccino.
Making a cup of .
Making a cup of espresso.

Default parameter values may be scalar values, arrays, the special type null, and as of PHP 8.1.0, objects using the new ClassName() syntax.

Example #5 Using non-scalar types as default values

function makecoffee($types = array("cappuccino"), $coffeeMaker = NULL)
{
    $device = is_null($coffeeMaker) ? "hands" : $coffeeMaker;
    return "Making a cup of ".join(", ", $types)." with $device.\n";
}
echo makecoffee();
echo makecoffee(array("cappuccino", "lavazza"), "teapot");?>

Example #6 Using objects as default values (as of PHP 8.1.0)

class DefaultCoffeeMaker {
    public function brew() {
        return 'Making coffee.';
    }
}
class FancyCoffeeMaker {
    public function brew() {
        return 'Crafting a beautiful coffee just for you.';
    }
}
function makecoffee($coffeeMaker = new DefaultCoffeeMaker)
{
    return $coffeeMaker->brew();
}
echo makecoffee();
echo makecoffee(new FancyCoffeeMaker);
?>

The default value must be a constant expression, not (for example) a variable, a class member or a function call.

Note that any optional arguments should be specified after any required arguments, otherwise they cannot be omitted from calls. Consider the following example:

Example #7 Incorrect usage of default function arguments

function makeyogurt($container = "bowl", $flavour)
{
    return "Making a $container of $flavour yogurt.\n";
}

 echo

The above example will output:

Fatal error: Uncaught ArgumentCountError: Too few arguments
 to function makeyogurt(), 1 passed in example.php on line 42

Now, compare the above with this:

Example #8 Correct usage of default function arguments

function makeyogurt($flavour, $container = "bowl")
{
    return "Making a $container of $flavour yogurt.\n";
}

 echo

The above example will output:

Making a bowl of raspberry yogurt.

As of PHP 8.0.0, named arguments can be used to skip over multiple optional parameters.

Example #9 Correct usage of default function arguments

function makeyogurt($container = "bowl", $flavour = "raspberry", $style = "Greek")
{
    return "Making a $container of $flavour $style yogurt.\n";
}

echo

The above example will output:

Making a bowl of raspberry natural yogurt.

As of PHP 8.0.0, declaring mandatory arguments after optional arguments is deprecated. This can generally be resolved by dropping the default value, since it will never be used. One exception to this rule are arguments of the form Type $param = null, where the null default makes the type implicitly nullable. This usage remains allowed, though it is recommended to use an explicit nullable type instead.

Example #10 Declaring optional arguments after mandatory arguments

 function foo($a = [], $b) {} // Default not used; deprecated as of PHP 8.0.0
 function foo($a, $b) {}      // Functionally equivalent, no deprecation noticefunction bar(A $a = null, $b) {} // Still allowed; $a is required but nullable
 function bar(?A $a, $b) {}       // Recommended
 ?>

Note: As of PHP 7.1.0, omitting a parameter which does not specify a default throws an ArgumentCountError; in previous versions it raised a Warning.

Note: Arguments that are passed by reference may have a default value.

Variable-length argument lists

PHP has support for variable-length argument lists in user-defined functions by using the ... token.

Note: It is also possible to achieve variable-length arguments by using func_num_args(), func_get_arg(), and func_get_args() functions. This technique is not recommended as it was used prior to the introduction of the ... token.

Argument lists may include the ... token to denote that the function accepts a variable number of arguments. The arguments will be passed into the given variable as an array; for example:

Example #11 Using ... to access variable arguments

function sum(...$numbers) {
    $acc = 0;
    foreach ($numbers as $n) {
        $acc += $n;
    }
    return $acc;
}

echo

The above example will output:

... can also be used when calling functions to unpack an array or Traversable variable or literal into the argument list:

Example #12 Using ... to provide arguments

function add($a, $b) {
    return $a + $b;
}

echo

The above example will output:

You may specify normal positional arguments before the ... token. In this case, only the trailing arguments that don't match a positional argument will be added to the array generated by ....

It is also possible to add a type declaration before the ... token. If this is present, then all arguments captured by ... must match that parameter type.

Example #13 Type declared variable arguments

function total_intervals($unit, DateInterval ...$intervals) {
    $time = 0;
    foreach ($intervals as $interval) {
        $time += $interval->$unit;
    }
    return $time;
}$a = new DateInterval('P1D');
$b = new DateInterval('P2D');
echo total_intervals('d', $a, $b).' days';// This will fail, since null isn't a DateInterval object.
echo total_intervals('d', null);
?>

The above example will output:

3 days
Catchable fatal error: Argument 2 passed to total_intervals() must be an instance of DateInterval, null given, called in - on line 14 and defined in - on line 2

Finally, variable arguments can also be passed by reference by prefixing the ... with an ampersand (&).

Older versions of PHP

No special syntax is required to note that a function is variadic; however access to the function's arguments must use func_num_args(), func_get_arg() and func_get_args().

The first example above would be implemented as follows in old versions of PHP:

Example #14 Accessing variable arguments in old PHP versions

function sum() {
    $acc = 0;
    foreach (func_get_args() as $n) {
        $acc += $n;
    }
    return $acc;
}

echo

The above example will output:

Named Arguments

PHP 8.0.0 introduced named arguments as an extension of the existing positional parameters. Named arguments allow passing arguments to a function based on the parameter name, rather than the parameter position. This makes the meaning of the argument self-documenting, makes the arguments order-independent and allows skipping default values arbitrarily.

Named arguments are passed by prefixing the value with the parameter name followed by a colon. Using reserved keywords as parameter names is allowed. The parameter name must be an identifier, specifying dynamically is not allowed.

Example #15 Named argument syntax

myFunction(paramName: $value);
array_foobar(array: $value);// NOT supported.
function_name($variableStoringParamName: $value);
?>

Example #16 Positional arguments versus named arguments

// Using positional arguments:
array_fill(0, 100, 50);// Using named arguments:
array_fill(start_index: 0, count: 100, value: 50);
?>

The order in which the named arguments are passed does not matter.

Example #17 Same example as above with a different order of parameters

array_fill(value: 50, count: 100, start_index: 0);
?>

Named arguments can be combined with positional arguments. In this case, the named arguments must come after the positional arguments. It is also possible to specify only some of the optional arguments of a function, regardless of their order.

Example #18 Combining named arguments with positional arguments

htmlspecialchars($string, double_encode: false);
// Same as
htmlspecialchars($string, ENT_QUOTES | ENT_SUBSTITUTE | ENT_HTML401, 'UTF-8', false);
?>

Passing the same parameter multiple times results in an Error exception.

Example #19 Error thrown when passing the same parameter multiple times

function foo($param) { ... }foo(param: 1, param: 2);
// Error: Named parameter $param overwrites previous argument
foo(1, param: 2);
// Error: Named parameter $param overwrites previous argument
?>

As of PHP 8.1.0, it is possible to use named arguments after unpacking the arguments. A named argument must not override an already unpacked arguments.

Example #20 Use named arguments after unpacking

function foo($a, $b, $c = 3, $d = 4) {
  return $a + $b + $c + $d;
}var_dump(foo(...[1, 2], d: 40)); // 46
var_dump(foo(...['b' => 2, 'a' => 1], d: 40)); // 46var_dump(foo(...[1, 2], b: 20)); // Fatal error. Named parameter $b overwrites previous argument
?>

php at richardneill dot org ¶

7 years ago

To experiment on performance of pass-by-reference and pass-by-value, I used this  script. Conclusions are below.

#!/usr/bin/php
function sum($array,$max){   //For Reference, use:  "&$array"
    $sum=0;
    for ($i=0; $i<2; $i++){
        #$array[$i]++;        //Uncomment this line to modify the array within the function.
        $sum += $array[$i]; 
    }
    return ($sum);
}$max = 1E7                  //10 M data points.
$data = range(0,$max,1);$start = microtime(true);
for ($x = 0 ; $x < 100; $x++){
    $sum = sum($data, $max);
}
$end =  microtime(true);
echo "Time: ".($end - $start)." s\n";/* Run times:
#    PASS BY    MODIFIED?   Time
-    -------    ---------   ----
1    value      no          56 us
2    reference  no          58 us

3    valuue     yes         129 s
4    reference  yes         66 us

Conclusions:

1. PHP is already smart about zero-copy / copy-on-write. A function call does NOT copy the data unless it needs to; the data is
   only copied on write. That's why  #1 and #2 take similar times, whereas #3 takes 2 million times longer than #4.
   [You never need to use &$array to ask the compiler to do a zero-copy optimisation; it can work that out for itself.]

2. You do use &$array  to tell the compiler "it is OK for the function to over-write my argument in place, I don't need the original
   any more." This can make a huge difference to performance when we have large amounts of memory to copy.
   (This is the only way it is done in C, arrays are always passed as pointers)

3. The other use of & is as a way to specify where data should be *returned*. (e.g. as used by exec() ).
   (This is a C-like way of passing pointers for outputs, whereas PHP functions normally return complex types, or multiple answers
   in an array)

4. It's  unhelpful that only the function definition has &. The caller should have it, at least as syntactic sugar. Otherwise
   it leads to unreadable code: because the person reading the function call doesn't expect it to pass by reference. At the moment,
   it's necessary to write a by-reference function call with a comment, thus:
    $sum = sum($data,$max);  //warning, $data passed by reference, and may be modified.

5. Sometimes, pass by reference could be at the choice of the caller, NOT the function definitition. PHP doesn't allow it, but it
   would be meaningful for the caller to decide to pass data in as a reference. i.e. "I'm done with the variable, it's OK to stomp
   on it in memory".
*/

LilyWhite ¶

11 months ago

It is worth noting that you can use functions as function arguments

function run($op, $a, $b) {
  return $op($a, $b);
}$add = function($a, $b) {
  return $a + $b;
};$mul = function($a, $b) {
  return $a * $b;
};

echo

gabriel at figdice dot org ¶

6 years ago

A function's argument that is an object, will have its properties modified by the function although you don't need to pass it by reference.

$x = new stdClass();
$x->prop = 1;

function

boan dot web at outlook dot com ¶

4 years ago

Quote:

"The declaration can be made to accept NULL values if the default value of the parameter is set to NULL."

But you can do this (PHP 7.1+):

function foo(?string $bar) {
    //...
}foo(); // Fatal error
foo(null); // Okay
foo('Hello world'); // Okay
?>

Hayley Watson ¶

5 years ago

There are fewer restrictions on using ... to supply multiple arguments to a function call than there are on using it to declare a variadic parameter in the function declaration. In particular, it can be used more than once to unpack arguments, provided that all such uses come after any positional arguments.

$array1

Sergio Santana: ssantana at tlaloc dot imta dot mx ¶

16 years ago

PASSING A "VARIABLE-LENGTH ARGUMENT LIST OF REFERENCES" TO A FUNCTION
As of PHP 5, Call-time pass-by-reference has been deprecated, this represents no problem in most cases, since instead of calling a function like this:
   myfunction($arg1, &$arg2, &$arg3);

you can call it
   myfunction($arg1, $arg2, $arg3);

provided you have defined your function as
   function myfuncion($a1, &$a2, &$a3) { // so &$a2 and &$a3 are
                                                             // declared to be refs.
    ...
   }

However, what happens if you wanted to pass an undefined number of references, i.e., something like:
   myfunction(&$arg1, &$arg2, ..., &$arg-n);?
This doesn't work in PHP 5 anymore.

In the following code I tried to amend this by using the
array() language-construct as the actual argument in the
call to the function.

function aa ($A) {
    // This function increments each
    // "pseudo-argument" by 2s
    foreach ($A as &$x) {
      $x += 2;
    }
  }$x = 1; $y = 2; $z = 3;aa(array(&$x, &$y, &$z));
  echo "--$x--$y--$z--\n";
  // This will output:
  // --3--4--5--
?>

I hope this is useful.

Sergio.

catman at esteticas dot se ¶

6 years ago

I wondered if variable length argument lists and references works together, and what the syntax might be. It is not mentioned explicitly yet in the php manual as far as I can find. But other sources mention the following syntax "&...$variable" that works in php  5.6.16.

function foo(&...$args)
{
    $i = 0;
    foreach ($args as &$arg) {
        $arg = ++$i;
    }
}
foo($a, $b, $c);
echo 'a = ', $a, ', b = ', $b, ', c = ', $c;
?>
Gives
a = 1, b = 2, c = 3

jcaplan at bogus dot amazon dot com ¶

16 years ago

In function calls, PHP clearly distinguishes between missing arguments and present but empty arguments.  Thus:

function f( $x = 4 ) { echo $x . "\\n"; }
f(); // prints 4
f( null ); // prints blank line
f( $y ); // $y undefined, prints blank line
?>

The utility of the optional argument feature is thus somewhat diminished.  Suppose you want to call the function f many times from function g, allowing the caller of g to specify if f should be called with a specific value or with its default value:

function f( $x = 4 ) {echo $x . "\\n"; }// option 1: cut and paste the default value from f's interface into g's
function g( $x = 4 ) { f( $x ); f( $x ); }// option 2: branch based on input to g
function g( $x = null ) { if ( !isset( $x ) ) { f(); f() } else { f( $x ); f( $x ); } }
?>

Both options suck.

The best approach, it seems to me, is to always use a sentinel like null as the default value of an optional argument.  This way, callers like g and g's clients have many options, and furthermore, callers always know how to omit arguments so they can omit one in the middle of the parameter list.

function f( $x = null ) { if ( !isset( $x ) ) $x = 4; echo $x . "\\n"; }

function

info at keraweb dot nl ¶

4 years ago

You can use a class constant as a default parameter.

class A {
    const FOO = 'default';
    function bar( $val = self::FOO ) {
        echo $val;
    }
}$a = new A();
$a->bar(); // Will echo "default"

Hayley Watson ¶

5 years ago

If you use ... in a function's parameter list, you can use it only once for obvious reasons. Less obvious is that it has to be on the LAST parameter; as the manual puts it: "You may specify normal positional arguments BEFORE the ... token. (emphasis mine).

function variadic($first, ...$most, $last)
{/*etc.*/}variadic(1, 2, 3, 4, 5);
?>
results in a fatal error, even though it looks like the Thing To Do™ would be to set $first to 1, $most to [2, 3, 4], and $last to 5.

Horst Schirmeier ¶

8 years ago

Editor's note: what is expected here by the parser is a non-evaluated expression. An operand and two constants requires evaluation, which is not done by the parser. However, this feature is included as of PHP 5.6.0. See this page for more information: http://php.net/migration56.new-features#migration56.new-features.const-scalar-exprs
--------

"The default value must be a constant expression" is misleading (or even wrong).  PHP 5.4.4 fails to parse this function definition:

function htmlspecialchars_latin1($s, $flags = ENT_COMPAT | ENT_HTML401) {}

This yields a " PHP Parse error:  syntax error, unexpected '|', expecting ')' " although ENT_COMPAT|ENT_HTML401 is certainly what a compiler-affine person would call a "constant expression".

The obvious workaround is to use a single special value ($flags = NULL) as the default, and to set it to the desired value in the function's body (if ($flags === NULL) { $flags = ENT_COMPAT | ENT_HTML401; }).

tesdy14 at gmail dot com ¶

9 months ago

function my_fonction(string $value) {
    echo $value . PHP_EOL;
}

my_fonction(['foo' => 'ko', 'bar' => 'not', 'goodValue' => 'Oh Yeah']['goodValue']);

// return 'Oh Yeah'

// This may sound strange, anyway it's very useful in a foreach (or other conditional structure).

$expectedStatusCodes = [404, 403];

function getValueFromArray(string $value): string
{
    return $value . PHP_EOL;
}

foreach ($expectedStatusCodes as $code) {
    echo $currentUserReference = getValueFromArray(
        [
            404 => "Doesn't exist",
            403 => 'Forbidden',
            200 => "you're welcome"
        ][$code]
    );
}

TwystO ¶

4 months ago

As stated in the documentation, the ... token can be used to pass an array of parameters to a function.

But it also works for class constructors as you can see below :

class Courtesy {
    public string $firstname;
    public string $lastname;

        public function

Simmo at 9000 dot 000 ¶

5 months ago

For anyone just getting started with php or searching, for an understanding, on what this page describes as a "... token" in Variable-length arguments:
https://www.php.net/manual/en/functions.arguments.php#functions.variable-arg-list


  func

rsperduta at gmail dot com ¶

1 year ago

About example #2: That little comma down at the end and often obscured by a line comment is easily over looked. I think it's worth considering putting it at the head of the next line to make clear what it's relationship is to the surrounding lines. Consider how much clearer it's continuation as a list of parameters:

function takes_many_args(
    $first_arg // some description
    , $second_arg // another comment
    , $a_very_long_argument_name = something($complicated) // IDK
    , $arg_with_default = 5
    , $again = 'a default string', // IMHO this trailing comma encourages illegible code and not being permitted seemed  a good idea lost with 8.0.0.
) {
    // ...
}
?>

This principle can be applied equally to complicated boolean expressions of an "if" statement (or the parts of a for statement).

igorsantos07 at gmail dot com ¶

4 years ago

PHP 7+ does type coercion if strict typing is not enabled, but there's a small gotcha: it won't convert null values into anything.

You must explicitly set your default argument value to be null (as explained in this page) so your function can also receive nulls.

For instance, if you type an argument as "string", but pass a null variable into it, you might expect to receive an empty string, but actually, PHP will yell at you a TypeError.

function null_string_wrong(string $str) {
  var_dump($str);
}
function null_string_correct(string $str = null) {
  var_dump($str);
}
$null = null;
null_string_wrong('a');     //string(1) "a"
null_string_correct('a');   //string(1) "a"
null_string_correct();      //NULL
null_string_correct($null); //NULL
null_string_wrong($null);   //TypeError thrown
?>

John ¶

15 years ago

This might be documented somewhere OR obvious to most, but when passing an argument by reference (as of PHP 5.04) you can assign a value to an argument variable in the function call. For example:

function my_function($arg1, &$arg2) {
  if ($arg1 == true) {
    $arg2 = true;
  }
}
my_function(true, $arg2 = false);
echo $arg2;

outputs 1 (true)

my_function(false, $arg2 = false);
echo $arg2;

outputs 0 (false)

dmitry dot balabka at gmail dot com ¶

3 years ago

There is a possibility to use parent keyword as type hint which is not mentioned in the documentation.

Following code snippet will be executed w/o errors on PHP version 7. In this example, parent keyword is referencing on ParentClass instead of ClassTrait.
namespace TestTypeHints;

class

shaman_master at list dot ru ¶

2 years ago

You can use the class/interface as a type even if the class/interface is not  defined yet or the class/interface implements current class/interface.
interface RouteInterface
{
    public function getGroup(): ?RouteGroupInterface;
}
interface RouteGroupInterface extends RouteInterface
{
    public function set(RouteInterface $item);
}
?>
'self' type - alias to current class/interface, it's not changed in implementations. This code looks right but throw error:
class Route
{
    protected $name;
     // method must return Route object
    public function setName(string $name): self
    {
         $this->name = $name;
         return $this;
    }
}
class RouteGroup extends Route
{
    // method STILL must return only Route object
    public function setName(string $name): self
    {
         $name .= ' group';
         return parent::setName($name);
    }
}
?>