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It just took me a while to really understand the differences between this three. But hopefully (never say never ;-), now i got it. A callback simple describes, that a function awaits another function as parameter. This functions can be an existing one or a "on the fly created on" with the power of create_function.

A lambda function is a function without a function name. The reference is stored in a variable. You can use this variable to handle it over to methods like usort. As everybody i will use a sorting lambda function for showing what i mean.

$lengthOfStringTwo) { $sorter = 1; } elseif ($lengthOfStringOne < $lengthOfStringTwo) { $sorter = -1; } return $sorter; }; $names = array( 'Brian W. Kernighan', 'Dennis Ritchie' ); usort($names, $mySorter); echo xdebug_var_dump($names); ?>

It is also possible to define the $mySorter directly in unsort as second parameter like

usort($names, function($stringOne, $stringTwo { ... });

if you like that.

A closure is a function that surrounds (i do not want to use the word enclose ;-)) the lambda function. That has the sideeffect that the closure itself conserves their own context. An easy example is a simple logger.

setMessage($message); $myDatabaseInfoLogTable->setTimestamp(mktime()); $status = $myDatabaseInfoLogTable->save(); break; case 'error': $myFileErrorLog = new ErrorLog(); $myFileErrorLog->addMessage(mktime() . "\t" . $message); $status = $myFileErrorLog->save(); break; } return $status; }; } $infoLogger = myClosureLogger('info'); $errorLogger = myClosureLogger('error'); $infoLogger('This is a info log'); $errorLogger('This is an error log'); ?>

The positiv thing about closures is, that the code footprint can be reduced (you even can use closures inside objects - even as static if you do not need to access on the object itself with $this). The negativ thing is, that you can not use interfaces which implies a lose of security.