14.2 Class Type Hints
The class type hint feature is available
in PHP5.
PHP is a loosely typed language, and this allows different types of
data to be passed as parameters into functions. When user-defined
functions or class member functions are designed to work with object
parameters, it is often useful to check the type of object before it
is used. PHP5 allows you to specify the type of object parameter with
a class type hint. Consider the following
example that defines a function to return information about
Shape objects:
// User-defined function that returns information about a Shape
// object
function shapeInfo(Shape $shape)
{
return "I have a {$s->color( )} shape with {$s->sides( )} sides";
}
The definition of the function shapeInfo(
)
includes the class type hint
Shape before the parameter
$shape. This instructs PHP to check the class of
$shape when the script is run. If the function is
called with an object that is not a Shape, or
even a value that was not an object, PHP causes the script to
terminate with a fatal error.
Using class type hints is the equivalent of checking the parameter
with the instanceof keyword. Using this approach,
the shapeInfo( ) function could be rewritten as:
// User-defined function that returns information about a Shape
// object
function shapeInfo($shape)
{
if (not $shape instanceof Shape)
die ("Parameter not a Shape object");
return "I have a {$s->color( )} shape with {$s->sides( )} sides";
}
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