I was just thinking about a way to create a singleton where you only need to run the instance() function only one time with an argument. And I came up with this solution: (maybe it's useful for other users)
<?php
class Singleton {
private $arg = "";
private function __construct($arg) {
$this->arg = $arg;
}
public static function instance() {
static $_instance = null;
if(func_num_args() == 0 && $_instance == null) {
$_instance = new Singleton(func_get_arg(0));
}
}
}
// first time
$singleton = Singleton::instance("foobar");
// later in your code (in other class and/or function)
$singleton = Singleton::instance();
?>
func_get_arg
(PHP 4, PHP 5)
func_get_arg — 引数のリストから要素をひとつ返す
説明
mixed func_get_arg ( int $arg_num )ユーザが定義した関数の引数リストから、指定した引数を取得します。
この関数は、 func_num_args()および func_get_args()と組み合わせて使用され、これにより ユーザ定義の関数が可変長の引数リストをとることができるようになります。
パラメータ
- arg_num
引数の位置。関数の引数はゼロから数え始めます。
返り値
指定した引数、あるいはエラー時に FALSE を返します。
エラー / 例外
ユーザ定義関数の外部からコールされた場合、あるいは arg_num が実際に渡された引数の数より多い場合に警告を発生します。
例
例 732. func_get_arg() の例
<?php
function foo()
{
$numargs = func_num_args();
echo "Number of arguments: $numargs<br />\n";
if ($numargs >= 2) {
echo "二番目の引数は " . func_get_arg(1) . " です。<br />\n";
}
}
foo (1, 2, 3);
?>
注意
注意: この関数は、 カレントスコープに依存してパラメータの詳細を決定しますので、 関数パラメータとして使用することはできません。 もし、この値を渡さなければならない場合、戻り値を変数に割り当て、 その変数を渡してください。
注意: この関数は、渡された引数のみのコピーを返します。 デフォルトの (渡されていない) 引数については感知しません。
参考
| func_get_args() |
| func_num_args() |
func_get_arg
Aries-Belgium
12-Jan-2007 03:44
12-Jan-2007 03:44
bishop
11-Dec-2004 02:58
11-Dec-2004 02:58
Regarding a "deferment" operator for dvogel at ssc dot wisc dot edu, pick your poison:
<?php
// using ternary operators
function pick($a,$b) { return (isset($a) ? $a : $b); }
$a = (pick($b,$c) ? pick($c,$d) : null);
?>
<?php
// using varargs function
function pick($a) {
$argc = func_num_args();
for ($i = 0; $i < $argc; $i++) {
$arg = func_get_arg($i);
if (! is_null($arg)) {
return $arg;
}
}
return null;
}
$a = pick($b, $c, $d);
?>
mw atto lanfear dotto com
08-Dec-2004 07:56
08-Dec-2004 07:56
func_get_arg() does not appear to be allowed to be used as a function argument itself within class constructors in PHP 5.0.2 (wonk-ay!!!):
<?php
class ABC
{
function __construct()
{
foreach (func_get_args() as $name => $value)
{
echo <<<EOT
<br/>
$name : $value <br/>
<br/>
EOT;
}
}
}
class DEF extends ABC
{
function __construct()
{
parent::__construct(func_get_arg(0),
func_get_arg(1),
func_get_arg(2));
}
}
$def = new DEF(123123, "asdfasdf", "blahblahblah");
?>
The above script generates:
Fatal error: func_get_arg(): Can't be used as a function parameter in c:\Inetpub\wwwroot\phpwasrc\chapter10\xxx.php on line 23
There are, however, no problems when passing these as parameters to regular functions.
dvogel at ssc dot wisc dot edu
22-Oct-2004 06:54
22-Oct-2004 06:54
I've always wants a deferment or cascade operator so that I could use this expression:
$a = $b ## $c ## $d;
and everything to the right of the assignment operator would evaluate to the left-most value that is not null. It is essentially a collapsed version of this:
if ($b) {
$a=$b;
} else {
if($c) {
$a=$c;
} else {
if ($d) {
$a = $d;
} else {
$a = null;
}
}
}
In leiu of this, I'm trying to make a function that takes a variable number of arguments and returns the first that is not null. I wan't to use this on some large-ish arrays, so I'd like to pass these by reference. However, call-time reference passing is disabled (and should be, imo) in newer versions of PHP. I'd like suggestions on how to pass both references and values to this function.
The only solution I can think of is setting variables to the reference of the array first. e.g.
$a = array( ... );
$b = 0;
$c = &a;
first_not_null($a, $b);
Does anyone know a better solution?
harald at triptop dot org
15-Sep-2004 07:09
15-Sep-2004 07:09
func_get_arg is useful, if you know the exact order of the arguments, or if the order doesn't matter. i use this function (or func_get_args) for example to create own sprintf wrappers.
if you want to pass a variable number of arguments to a function it's in my opinion better, to submit it as a key/value array e.g.:
<?php
functioncall(array("param1" => "...",...));
?>
and 'extract' the array inside the function. you don't need to do tricks like type-checking for parameter-recognition, in this case.
anders at ingemann dot fakestuff dot de
04-Jun-2004 10:16
04-Jun-2004 10:16
I actually think that there is need for such "do absolutely everything" functions. I use them mostly as tools for rapid prototyping.
And there is a method with which you may be able to pass several strings to a function: ereg();
Another use for such functions is to create little code snippets for other people out there. They won't have to edit the function any longer if they do not use a parameter. They just don't name it when calling the function.
This results in allrounder functions that are very robust in their use.Normally you just have a little code snippet (e.g. ip-blocking snippets). Through this type of programming you have whole functions.
27-May-2004 01:29
very clever unless you need to specify at least two parameters of the same type - which is which? Obviously, you may decide on some defaults, but then the whole thing gets ugly. What if you need a string ONLY if a boolean was also supplied? The type-checking becomes the main focus of your function, shit. For the sake of clean code you should specify a clean interface to your functions, and decide on what and where is passed as an argument. Yes, you can always code a do_absolutely_everything() function, but is there any sense?
anders at ingemann dot fakestuff dot de
30-Apr-2004 08:18
30-Apr-2004 08:18
A pretty cool thing for user defined functions is only to submit the needed parameters. If you call a function that has three optional parameters you have to define the two first ones (even if they should stay like the defined standard in the function) before your are able to tell the function what the third important parameter is. Instead you might as well just find out by the pattern or the type of the submitted parameter which variable it should be assigned to.
like this:
<?
function whatever()
{
for($i=0;$i<func_num_args();$i++)
{
if(is_bool(func_get_arg($i))) $log_ip=func_get_arg($i);
if(is_int(func_get_arg($i))) $limit=func_get_arg($i);
if(is_string(func_get_arg($i))) $name=func_get_arg($i);
}
}
?>
Now you can call the function with any parameter you want.
e.g.:
<? whatever(3600); ?>
in that case $limit would be defined with 3600.
It doesn't matter if you do this:
<? whatever(3600,false); ?>
or this:
<? whatever(3600,"blaaah"); ?>
or this:
<? whatever("blaaah",true,3600); ?>
You may also use ereg(). Through that you're able to use more than one parameter as a string.
hmm probably ereg() is the best solution...
never mind.
just check it out ;-)
mightye (at) mightye (dot) org
13-Mar-2004 02:45
13-Mar-2004 02:45
func_get_arg() returns a *copy* of the argument, to my knowledge there is no way to retrieve references to a variable number of arguments.
I have a module system in my game at http://lotgd.net where I'd like to be able to pass a variable number of arguments to functions in a module, and pass them by reference if the module asks for it by reference, but you can't accept optional parameters as references, nor can you retrieve the reference on a variable number of arguments. Looks like my modules will have to do with out the ability to accept parameters to their functions by reference.
martin at classaxe dot com
08-Jun-2002 02:55
08-Jun-2002 02:55
This function whilst elegant doesn't in itself avoid the problem of generating warning messages where variables are not set, unless of course you switched warnings off:
error_reporting(E_ERROR);
The answer for those of who like to see necessary warnings?
Call it like this:
@allSet($w, $x, $y, $z)
(Martin Francis)