php - What purpose does empty exception class serve? -

i have seen implementation exceptions like:

<?php  class teste extends exception {}  class mytest {      public function __construct() {         try{             throw new teste('this exception!');         }catch(exception $exc){             var_dump($exc);         }          echo '2';     } }  $o = new mytest(); 

where custom exception class teste defined kept empty above. purpose achieve? have used:

throw new exception('this exception') 

instead of

throw new teste('this exception') 

extending exception class useful because allows finer control on exception handling.

the class posted can used this:

try {     // code can throw exception, invalidargumentexception or teste     // depending on specific issue encountered  } catch (teste $e) {     // teste thrown when specific issue happens; requires particular handling     // f.e. can logged , ignored because program can continue  } catch (invalidargumentexception $e) {     // exception signals coding error;     // example, invalid type of argument passed function     // needs different handling teste; f.e. can logged     // , notification email sent developer } catch (exception $e) {     // generic exception type     // catches exceptions not caught other branches     // specific handling not possible them; log them , exit program } 

on other hand, class exception contains members , methods need use them. there no need add more members , method.

this why exception class extended children classes not provide new functionality (most of times).