create_function

Description

Creates an anonymous function from the parameters passed, and returns a unique name for it. Usually the args will be passed as a single quote delimited string, and this is also recommended for the code . The reason for using single quoted strings, is to protect the variable names from parsing, otherwise, if you use double quotes there will be a need to escape the variable names, e.g. \$avar .

You can use this function, to (for example) create a function from information gathered at run time:

例子 1. Creating an anonymous function with create_function() <?php $newfunc = create_function ( '$a,$b' , 'return "ln($a) + ln($b) = " . log($a * $b);' ); echo "New anonymous function: $newfunc \n " ; echo $newfunc ( 2 , M_E ) . "\n" ; // outputs // New anonymous function: lambda_1 // ln(2) + ln(2.718281828459) = 1.6931471805599 ?>

Or, perhaps to have general handler function that can apply a set of operations to a list of parameters:

例子 2. Making a general processing function with create_function() <?php function process ( $var1 , $var2 , $farr ) {     foreach ( $farr as $f ) {         echo $f ( $var1 , $var2 ) . "\n" ;     } } // create a bunch of math functions $f1 = 'if ($a >=0) {return "b*a^2 = ".$b*sqrt($a);} else {return false;}' ; $f2 = "return \"min(b^2+a, a^2,b) = \".min(\$a*\$a+\$b,\$b*\$b+\$a);" ; $f3 = 'if ($a > 0 && $b != 0) {return "ln(a)/b = ".log($a)/$b; } else { return false; }' ; $farr = array(      create_function ( '$x,$y' , 'return "some trig: ".(sin($x) + $x*cos($y));' ),      create_function ( '$x,$y' , 'return "a hypotenuse: ".sqrt($x*$x + $y*$y);' ),      create_function ( '$a,$b' , $f1 ),      create_function ( '$a,$b' , $f2 ),      create_function ( '$a,$b' , $f3 )     ); echo "\nUsing the first array of anonymous functions\n" ; echo "parameters: 2.3445, M_PI\n" ; process ( 2.3445 , M_PI , $farr ); // now make a bunch of string processing functions $garr = array(      create_function ( '$b,$a' , 'if (strncmp($a, $b, 3) == 0) return "** \"$a\" ' .      'and \"$b\"\n** Look the same to me! (looking at the first 3 chars)";' ),      create_function ( '$a,$b' , '; return "CRCs: " . crc32($a) . " , ".crc32(b);' ),      create_function ( '$a,$b' , '; return "similar(a,b) = " . similar_text($a, $b, &$p) . "($p%)";' )     ); echo "\nUsing the second array of anonymous functions\n" ; process ( "Twas brilling and the slithy toves" , "Twas the night" , $garr ); ?> and when you run the code above, the output will be: Using the first array of anonymous functions parameters: 2.3445, M_PI some trig: -1.6291725057799 a hypotenuse: 3.9199852871011 b*a^2 = 4.8103313314525 min(b^2+a, a^2,b) = 8.6382729035898 ln(a/b) = 0.27122299212594 Using the second array of anonymous functions ** "Twas the night" and "Twas brilling and the slithy toves" ** Look the same to me! (looking at the first 3 chars) CRCs: -725381282 , 1908338681 similar(a,b) = 11(45.833333333333%)

But perhaps the most common use for of lambda-style (anonymous) functions is to create callback functions, for example when using array_walk() or usort()

例子 3. Using anonymous functions as callback functions <?php $av = array( "the " , "a " , "that " , "this " ); array_walk ( $av , create_function ( '&$v,$k' , '$v = $v . "mango";' )); print_r ( $av ); ?> outputs: Array ( [0] => the mango [1] => a mango [2] => that mango [3] => this mango ) an array of strings ordered from shorter to longer <?php $sv = array( "small" , "larger" , "a big string" , "it is a string thing" ); print_r ( $sv ); ?> outputs: Array ( [0] => small [1] => larger [2] => a big string [3] => it is a string thing ) sort it from longer to shorter <?php usort ( $sv , create_function ( '$a,$b' , 'return strlen($b) - strlen($a);' )); print_r ( $sv ); ?> outputs: Array ( [0] => it is a string thing [1] => a big string [2] => larger [3] => small )