How is the keyword 'finally' meant to be used in PHP?

Question

So, I have been reading about the exceptions today on the PHP online manual, and realize I have yet to understand the purpose or real necessity of the finally keyword. I have read some posts here, so my question is slightly different.

I understand that we can use finally in this way:

function hi(){
    return 'Hi';
}


try {
    throw new LogicException("Throw logic \n");
} catch (InvalidArgumentException $e) {
    echo $e->getMessage(); 
}

echo hi();

output:

Fatal error:  Uncaught LogicException: Throw Logic in C:\Users\...a.php:167
Stack trace:
#0 {main}
  thrown in C:\Users\...a.php on line 167

So, in this case the function hi(); is not being execute and for a good reason. I understand if exception is not handled php interpreter halts the script. good. So far from what I read, finally enables us to execute the function hi(); even if the exception is not handled (even though I don't know why)

So, this one I understand.

try {
    throw new LogicException("Throw logic \n");
} catch (InvalidArgumentException $e) {
    echo $e->getMessage(); 
}finally{
    echo hi();
}

output:

Hi
Fatal error:  Uncaught LogicException: Throw Logic in C:\Users\...a.php:167
Stack trace:
#0 {main}
  thrown in C:\Users\...a.php on line 167

This on should the exception error as well as the 'hi' message from the function, even those I don't know any usage for this. But what I don't undersand this, even if we catch the LogicException with catch (LogicException $e) and no exceptions were thrown still we would see the function being execute, and we would see the 'hi' message. as in this example

try {
    throw new LogicException("Throw logic \n");
} catch (LogicException $e) {
    echo $e->getMessage(); 
}finally{
    echo hi();
}

outputs

// Throw logic 
// Hi

So, we still see the function hi() executed even though we have no Uncaught exceptions. Why and what is the use for this? I thought the finally block was to be used as a last resort in case the exceptions were not caught, even if that wasn't the case then why is it the use to run it?

Answer 1

Finally should contain any code which needs to be executed regardless of whether there's an exception or not.

Without finally:

try {
   $handle = fopen("file.txt");
   //Do stuff
   fclose($handle);
   return something;
} catch (Exception $e) {
   // Log
   if (isset($handle) && $handle !== false) {
      fclose($handle);
   }     
}

With finally:

try {
   $handle = fopen("file.txt");
   return something;
} catch (Exception $e) {
   // Log
} finally {
   if (isset($handle) && $handle !== false) {
      fclose($handle);
   }     
}

Offers a bit of decluttering in the case that you need to free up a resource after a function has returned.

This becomes even more useful in a case like the following:

 try {
     $handle = fopen("file.txt");
     if (case1) { return result1; }  
     if (case2) { return result2; }
     if (case3) { return result3; }
     if (case4) { return result4; }

 } finally {
     if (isset($handle) && $handle !== false) {
          fclose($handle);
       }    
 }

In this case you can reduce all the required fclose calls before each return to a single fclose call that will be executed right before the method returns but after any other code.

Answer 2

try {
    throw new LogicException("Throw logic \n"); -> LogicException thrown
} catch (InvalidArgumentException $e) { -> LogicException not catched
    echo $e->getMessage(); 
}finally{
    echo hi(); -> code executed. "Hi" printed out
}

LogicException is here -> Fatal error

so in this case:

try {
    throw new LogicException("Throw logic \n"); -> LogicException thrown
} catch (InvalidArgumentException $e) { -> LogicException not catched
    echo $e->getMessage(); 
}finally{
    echo hi(); -> code executed
    die();
}

no fatal error will be raised, because of die statement and the last variation:

try {
    throw new LogicException("Throw logic \n"); -> LogicException thrown
} catch (InvalidArgumentException $e) { -> LogicException not catched
    echo $e->getMessage(); 
} catch (LogicException $e) { -> LogicException catched
    echo $e->getMessage(); 
}finally{
    echo hi(); -> code executed
}

Answer 3

I made a little unit test to show how it is working

    $a = 'a';
    try {
        $a .= 'b';
    } catch (Exception $ex) {
        $a .= 'e';
    } finally {
        $a .= 'f';
    }
    $a .= 'x';

    $this->assertSame('abfx', $a);


    $a = 'a';
    try {
        $a .= 'b';
        throw new Exception();
        $a .= '1';
    } catch (Exception $ex) {
        $a .= 'e';
    } finally {
        $a .= 'f';
    }
    $a .= 'x';

    $this->assertSame('abefx', $a);


    $a = 'a';
    try {
        try {
            $a .= 'b';
            throw new Exception();
            $a .= '1';
        } catch (Exception $ex) {
            $a .= 'e';
            throw $ex;
            $a .= '2';
        } finally {
            $a .= 'f';
        }
        $a .= 'x';
    } catch (Exception $ex) {
        $a .= 'z';
    }

    $this->assertSame('abefz', $a);