with Hidden Features of PHP?




stackoverflow php tutorial (24)

My list.. most of them fall more under the "hidden features" than the "favorite features" (I hope!), and not all are useful, but .. yeah.

// swap values. any number of vars works, obviously  
list($a, $b) = array($b, $a);

// nested list() calls "fill" variables from multidim arrays:  
$arr = array(  
  array('aaaa', 'bbb'),  
  array('cc', 'd')  
);  
list(list($a, $b), list($c, $d)) = $arr;  
echo "$a $b $c $d"; // -> aaaa bbb cc d  

// list() values to arrays  
while (list($arr1[], $arr2[], $arr3[]) = mysql_fetch_row($res)) { .. }  
// or get columns from a matrix  
foreach($data as $row) list($col_1[], $col_2[], $col_3[]) = $row;

// abusing the ternary operator to set other variables as a side effect:  
$foo = $condition ? 'Yes' . (($bar = 'right') && false) : 'No' . (($bar = 'left') && false);  
// boolean False cast to string for concatenation becomes an empty string ''.  
// you can also use list() but that's so boring ;-)  
list($foo, $bar) = $condition ? array('Yes', 'right') : array('No', 'left');

You can nest ternary operators too, comes in handy sometimes.

// the strings' "Complex syntax" allows for *weird* stuff.  
// given $i = 3, if $custom is true, set $foo to $P['size3'], else to $C['size3']:  
$foo = ${$custom?'P':'C'}['size'.$i];  
$foo = $custom?$P['size'.$i]:$C['size'.$i]; // does the same, but it's too long ;-)  
// similarly, splitting an array $all_rows into two arrays $data0 and $data1 based  
// on some field 'active' in the sub-arrays:  
foreach ($all_rows as $row) ${'data'.($row['active']?1:0)}[] = $row;

// slight adaption from another answer here, I had to try out what else you could  
// abuse as variable names.. turns out, way too much...  
$string = 'f.> <!-? o+';  
${$string} = 'asdfasf';  
echo ${$string}; // -> 'asdfasf'  
echo $GLOBALS['f.> <!-? o+']; // -> 'asdfasf'  
// (don't do this. srsly.)

${''} = 456;  
echo ${''}; // -> 456  
echo $GLOBALS['']; // -> 456  
// I have no idea.  

Right, I'll stop for now :-)


Hmm, it's been a while..

// just discovered you can comment the hell out of php:
$q/* snarf */=/* quux */$_GET/* foo */[/* bar */'q'/* bazz */]/* yadda */;

So, just discovered you can pass any string as a method name IF you enclose it with curly brackets. You can't define any string as a method alas, but you can catch them with __call(), and process them further as needed. Hmmm....

class foo {
  function __call($func, $args) {
    eval ($func);
  }
}

$x = new foo;
$x->{'foreach(range(1, 10) as $i) {echo $i."\n";}'}();

Found this little gem in Reddit comments:

$foo = 'abcde';
$strlen = 'strlen';
echo "$foo is {$strlen($foo)} characters long."; // "abcde is 5 characters long."

You can't call functions inside {} directly like this, but you can use variables-holding-the-function-name and call those! (*and* you can use variable variables on it, too)

I know this sounds like a point-whoring question but let me explain where I'm coming from.

Out of college I got a job at a PHP shop. I worked there for a year and a half and thought that I had learned all there was to learn about programming.

Then I got a job as a one-man internal development shop at a sizable corporation where all the work was in C#. In my commitment to the position I started reading a ton of blogs and books and quickly realized how wrong I was to think I knew everything. I learned about unit testing, dependency injection and decorator patterns, the design principle of loose coupling, the composition over inheritance debate, and so on and on and on - I am still very much absorbing it all. Needless to say my programming style has changed entirely in the last year.

Now I find myself picking up a php project doing some coding for a friend's start-up and I feel completely constrained as opposed to programming in C#. It really bothers me that all variables at a class scope have to be referred to by appending '$this->' . It annoys me that none of the IDEs that I've tried have very good intellisense and that my SimpleTest unit tests methods have to start with the word 'test'. It drives me crazy that dynamic typing keeps me from specifying implicitly which parameter type a method expects, and that you have to write a switch statement to do method overloads. I can't stand that you can't have nested namespaces and have to use the :: operator to call the base class's constructor.

Now I have no intention of starting a PHP vs C# debate, rather what I mean to say is that I'm sure there are some PHP features that I either don't know about or know about yet fail to use properly. I am set in my C# universe and having trouble seeing outside the glass bowl.

So I'm asking, what are your favorite features of PHP? What are things you can do in it that you can't or are more difficult in the .Net languages?


Probably not many know that it is possible to specify constant "variables" as default values for function parameters:

function myFunc($param1, $param2 = MY_CONST)
{
//code...
}

Strings can be used as if they were arrays:

$str = 'hell o World';
echo $str; //outputs: "hell o World"

$str[0] = 'H';
echo $str; //outputs: "Hell o World"

$str[4] = null;
echo $str; //outputs: "Hello World"

One not so well known feature of PHP is extract(), a function that unpacks an associative array into the local namespace. This probably exists for the autoglobal abormination but is very useful for templating:

function render_template($template_name, $context, $as_string=false)
{
    extract($context);
    if ($as_string)
        ob_start();
    include TEMPLATE_DIR . '/' . $template_name;
    if ($as_string)
        return ob_get_clean();
}

Now you can use render_template('index.html', array('foo' => 'bar')) and only $foo with the value "bar" appears in the template.


The single most useful thing about PHP code is that if I don't quite understand a function I see I can look it up by using a browser and typing:

http://php.net/function

Last month I saw the "range" function in some code. It's one of the hundreds of functions I'd managed to never use but turn out to be really useful:

http://php.net/range

That url is an alias for http://us2.php.net/manual/en/function.range.php. That simple idea, of mapping functions and keywords to urls, is awesome.

I wish other languages, frameworks, databases, operating systems has as simple a mechanism for looking up documentation.


You can use minus character in variable names like this:

class style
{
  ....
  function set_bg_colour($c)
  {
    $this->{'background-color'} = $c;
  }
}

Why use it? No idea: maybe for a CSS model? Or some weird JSON you need to output. It's an odd feature :)


PHP enabled webspace is usually less expensive than something with (asp).net. You might call that a feature ;-)


I'm a little surprised no-one has mentioned it yet, but one of my favourite tricks with arrays is using the plus operator. It is a little bit like array_merge() but a little simpler. I've found it's usually what I want. In effect, it takes all the entries in the RHS and makes them appear in a copy of the LHS, overwriting as necessary (i.e. it's non-commutative). Very useful for starting with a "default" array and adding some real values all in one hit, whilst leaving default values in place for values not provided.

Code sample requested:

// Set the normal defaults.
$control_defaults = array( 'type' => 'text', 'size' => 30 );

// ... many lines later ...

$control_5 = $control_defaults + array( 'name' => 'surname', 'size' => 40 );
// This is the same as:
// $control_5 = array( 'type' => 'text', 'name' => 'surname', 'size' => 40 );

Variable variables and functions without a doubt!

$foo = 'bar';
$bar = 'foobar';
echo $$foo;    //This outputs foobar

function bar() {
    echo 'Hello world!';
}

function foobar() {
    echo 'What a wonderful world!';
}
$foo();    //This outputs Hello world!
$$foo();    //This outputs What a wonderful world!

The same concept applies to object parameters ($some_object->$some_variable);

Very, very nice. Make's coding with loops and patterns very easy, and it's faster and more under control than eval (Thanx @Ross & @Joshi Spawnbrood!).t


__autoload() (class-) files aided by set_include_path().

In PHP5 it is now unnecessary to specify long lists of "include_once" statements when doing decent OOP.

Just define a small set of directory in which class-library files are sanely structured, and set the auto include path:

set_include_path(get_include_path() . PATH_SEPARATOR . '../libs/');`

Now the __autoload() routine:

function __autoload($classname) {
    // every class is stored in a file "libs/classname.class.php"

    // note: temporary alter error_reporting to prevent WARNINGS
    // Do not suppress errors with a @ - syntax errors will fail silently!

    include_once($classname . '.class.php');
}

Now PHP will automagically include the needed files on-demand, conserving parsing time and memory.


HEREDOC syntax is my favourite hidden feature. Always difficult to find as you can't Google for <<< but it stops you having to escape large chunks of HTML and still allows you to drop variables into the stream.

echo <<<EOM
  <div id="someblock">
    <img src="{$file}" />
  </div>
EOM;

Here's one, I like how setting default values on function parameters that aren't supplied is much easier:

function MyMethod($VarICareAbout, $VarIDontCareAbout = 'yippie') { }

Arrays. Judging from the answers to this question I don't think people fully appreciate just how easy and useful Arrays in PHP are. PHP Arrays act as lists, maps, stacks and generic data structures all at the same time. Arrays are implemented in the language core and are used all over the place which results in good CPU cache locality. Perl and Python both use separate language constructs for lists and maps resulting in more copying and potentially confusing transformations.


The standard class is a neat container. I only learned about it recently.

Instead of using an array to hold serveral attributes

$person = array();
$person['name'] = 'bob';
$person['age'] = 5;

You can use a standard class

$person = new stdClass();
$person->name = 'bob';
$person->age = 5;

This is particularly helpful when accessing these variables in a string

$string = $person['name'] . ' is ' . $person['age'] . ' years old.';
// vs
$string = "$person->name is $person->age years old.";

Fast block comments

/*
    die('You shall not pass!');
//*/


//*
    die('You shall not pass!');
//*/

These comments allow you to toggle if a code block is commented with one character.


Range() isn't hidden per se, but I still see a lot of people iterating with:

for ($i=0; $i < $x; $i++) { 
    // code...
}

when they could be using:

foreach (range(0, 12) as $number) {
    // ...
}

And you can do simple things like

foreach (range(date("Y"), date("Y")+20) as $i)
{
print "\t<option value=\"{$i}\">{$i}</option>\n";
}

Stream Handlers allow you to extend the "FileSystem" with logic that as far as I know is quite difficult to do in most other languages.

For example with the MS-Excel Stream handler you can create a MS Excel file in the following way:

$fp = fopen("xlsfile://tmp/test.xls", "wb");
if (!is_resource($fp)) { 
    die("Cannot open excel file");
}

$data= array(
    array("Name" => "Bob Loblaw", "Age" => 50),  
    array("Name" => "Popo Jijo", "Age" => 75),  
    array("Name" => "Tiny Tim", "Age" => 90)
); 

fwrite($fp, serialize($data));
fclose($fp);

Include files can have a return value you can assign to a variable.

// config.php
return array(
    'db' => array(
        'host' => 'example.org',
        'user' => 'usr',
        // ...
    ),
    // ...
);

// index.php
$config = include 'config.php';
echo $config['db']['host']; // example.org

The static keyword is useful outside of a OOP standpoint. You can quickly and easily implement 'memoization' or function caching with something as simple as:

<?php
function foo($arg1)
{
    static $cache;

    if( !isset($cache[md5($arg1)]) )
    {
        // Do the work here
        $cache[md5($arg1)] = $results;
    }

    return $cache[md5($arg1)];
}
?>

The static keyword creates a variable that persists only within the scope of that function past the execution. This technique is great for functions that hit the database like get_all_books_by_id(...) or get_all_categories(...) that you would call more than once during a page load.

Caveat: Make sure you find out the best way to make a key for your hash, in just about every circumstance the md5(...) above is NOT a good decision (speed and output length issues), I used it for illustrative purposes. sprintf('%u', crc32(...)) or spl_object_hash(...) may be much better depending on the context.


Documentation. The documentation gets my vote. I haven't encountered a more thorough online documentation for a programming language - everything else I have to piece together from various websites and man pages.


Quick and dirty is the default.
The language is filled with useful shortcuts, This makes PHP the perfect candidate for (small) projects that have a short time-to-market. Not that clean PHP code is impossible, it just takes some extra effort and experience.

But I love PHP because it lets me express what I want without typing an essay.

PHP:

if (preg_match("/cat/","one cat")) {
   // do something
}

JAVA:

import java.util.regex.*;
Pattern p = Pattern.compile("cat");
Matcher m = p.matcher("one cat")
if (m.find()) {
  // do something
}

And yes, that includes not typing Int.


You can take advantage of the fact that the or operator has lower precedence than = to do this:

$page = (int) @$_GET['page'] 
  or $page = 1;

If the value of the first assignment evaluates to true, the second assignment is ignored. Another example:

$record = get_record($id) 
  or throw new Exception("...");

You can use functions with a undefined number of arguments using the func_get_args().

<?php

function test() {

    $args = func_get_args();
    echo $args[2]; // will print 'd'
    echo $args[1]; // will print 3
}

test(1,3,'d',4);

?>

One nice feature of PHP is the CLI. It's not so "promoted" in the documentation but if you need routine scripts / console apps, using cron + php cli is really fast to develop!


I'm a bit like you, I've coded PHP for over 8 years. I had to take a .NET/C# course about a year ago and I really enjoyed the C# language (hated ASP.NET) but it made me a better PHP developer.

PHP as a language is pretty poor, but, I'm extremely quick with it and the LAMP stack is awesome. The end product far outweighs the sum of the parts.

That said, in answer to your question:

http://uk.php.net/SPL

I love the SPL, the collection class in C# was something that I liked as soon as I started with it. Now I can have my cake and eat it.

Andrew





hidden-features