ExceptionsNeedToBeUseful

Okay, so we have this low-level library that is calling some code that handles numbers, and the functions it calls may generate PHP exceptions.

function lowLevelLibraryFunction() {
  //Call bar1 that may throw CastException
  //Call bar2 that may throw IntegerOutOfRangeException
  //Call bar3 that may throw FloatOutOfRangeException
}

And in our business domain we have function foo() which calls highLevelLbiraryFunction() which calls mediumLevelLibraryFunction() cwhich alls lowLevelLibraryFunction().

You either have to do this:
try {
    foo();
}
catch (CastException $ce) { throw new BusinessLogicException($ce) }
catch (IntegerOutOfRangeException $ioor) {throw new BusinessLogicException($ioor)}
catch (FloatOutOfRangeException $foor ) { throw new BusinessLogicException($foor) } 

As it's only at the application level that you can turn a 'functional' exception into a 'business logic' or domain specific exception. And it's this which makes people catch \Exception rather than individual exceptions.



If all of the number casting/checking functions threw the same exception then the low-level function would look like:

function lowLevelLibraryFunction() {
  //Call bar1 that may throw NumberException
  //Call bar2 that may throw NumberException
  //Call bar3 that may throw NumberException
}

And you could just this in your application level:

try {
    foo();
}
catch (NumberException $ce) { 
	throw new BusinessLogicException($ce) 
}

If you really wanted to have specific errors, you are still able to do so by catering for them in your lowLevel function even with a more generic exception being thrown.

function lowLevelLibraryFunction() {
    try {
  		//Call bar1 that may throw NumberException
  	}
  	catch(NumberException $e) {
  		throw new Bar1SpecificException
  	}
  	try {
  		//Call bar2 that may throw NumberException
  	}
  	catch(NumberException $e) {
  		throw new Bar2SpecificException
  	}
  	
  	try {
  		//Call bar3 that may throw NumberException
  	}
  	catch(NumberException $e) {
  		throw new Bar3SpecificException
  	}
}


And yes this is why I agree with Levi, having to catch exceptions is not as nice as being able to just check if the casting is going to work or not.

function lowLevelLibraryFunction() {
    if (CastableToInt($x) == false) {
        throw new Bar1SpecificException
    }
    
    if (inIntNumberRange($y) == false) {
        throw new Bar2SpecificException();
    }
    
    if (CastableToFloat($z) == false) {
        throw new Bar3SpecificException
    }
    
    //Numbers are safe.
    bar1($x);
    bar2($y);
    bar3($z)
}