Exceptions handlers (catch) are evaluated in the order they are written. Once a match is found, the evaluation stops.
In some contexts a catch block is dead code as it will never catch any exception:
- If there is a handler for a base class followed by a handler for class derived from that base class, the second handler will never trigger: the
handler for the base class will match the derived class, and will be the only executed handler.
- When multiple
catch blocks try to catch the same exception class, only the first one will be executed.
This rule raises an issue when a catch block catches every exception before a later catch block could catch it.
Noncompliant code example
class MyException extends Exception {}
class MySubException extends MyException {}
try {
doSomething();
} catch (MyException $e) {
echo $e;
} catch (MySubException $e) { // Noncompliant: MySubException is a subclass of MyException
echo "Never executed";
}
Compliant solution
class MyException extends Exception {}
class MySubException extends MyException {}
try {
doSomething();
} catch (MySubException $e) {
echo "Executed";
} catch (MyException $e) {
echo $e;
}
