Creating Anonymous Functions

It is possible to create functions on the fly during script execution. Because such functions are not themselves given a name, but are stored in variables or passed to other functions, they are known as anonymous functions. PHP provides the create_function() function for creating anonymous functions. create_function() requires two string arguments. The first argument should contain a comma-delimited list of argument variables, exactly the same as the argument variables you would include in a standard function declaration. The second argument should contain the function body.

Listing 6.15 creates a simple anonymous function to add two numbers together.

Listing 6.15 A Simple Anonymous Function
   1: <html>   2: <head>   3: <title>Listing 6.15</title>   4: </head>   5: <body>   6: <?php   7: $my_anon = create_function( '$a, $b', 'return $a+$b;' );   8: print $my_anon( 3, 9 );   9: // prints 12  10: ?>  11: </body>  12: </html> 

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As of this writing, the use of anonymous functions will cause a segmentation fault when running the Zend Optimizer.


Put these lines into a text file called anon.php, and place this file in your Web server document root. When you access this script through your Web browser, it produces the following:

 12 

Note that we use single quotes when passing arguments to create_function(). That saves us from having to escape the variable names within the arguments. We could have used double quotes, but the function call would have been a little more involved:

 $my_anon = create_function("\$a, \$b", "return \$a+\$b;"); 

So what is the use of anonymous functions? In practical terms, you will probably only use them when you need to pass callback functions to built-in functions. A callback function is generally written by the user and is designed to be invoked (usually repeatedly) by the function to which it is passed.

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The second argument to create_function() is the function body. Don't forget to end the last statement in this string with a semicolon. The interpreter will complain and your anonymous function will not be executed if you omit it.




Sams Teach Yourself PHP, MySQL and Apache in 24 Hours
Sams Teach Yourself PHP, MySQL and Apache in 24 Hours
ISBN: 067232489X
EAN: 2147483647
Year: 2005
Pages: 263

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