Pro PHP- Patterns, Frameworks, Testing and More

CHAPTER 13 ■ SPL EXCEPTIONS^193

Range Exceptions

The RangeException class is designed to handle range exceptions.

class RangeException extends RuntimeException

Like the domain, the range of a function is a math term. Contrary to popular belief, it

doesn’t mean the valid range of any input for a function. For example, the code in Listing 13-5

is semantically incorrect.

Listing 13-5. Improper Use of RangeException

function mathy($x) {

if ($x < 0) {

throw new RangeException('$x must be 0 or greater');

}

}

The range of a function has nothing to do with the inputs. Instead, that is the domain of

the function and should be handled with DomainException.

The range of a function is the set of all possible values for its result—its output. So,

RangeException is for throwing exceptions regarding the result of a function.

To understand where you might use RangeException, think of a temperature sensor. Its

valid range when interfaced will be to return a value between –50 and +50 Celsius. If it starts

returning a value outside this range, you know your sensor broke.

RangeException is a runtime exception, rather than a logical exception like DomainException,

because it refers to result data. Listing 13-6 shows the proper use of RangeException.

Listing 13-6. Proper Use of RangeException

class Sensor {

public static function getTemperature() {

return 51;

}

}

class Monitor {

public static function watch() {

$temp = Sensor::getTemperature();

if(($temp < -50) || ($temp > 50)) {

throw new RangeException('The sensor broke down.');

}

}

}

Monitor::watch();

McArthur_819-9C13.fm Page 193 Thursday, February 28, 2008 7:53 AM