Type casting is not validPHP-W1042

The value you are trying to cast into another type cannot be done. This would lead to a runtime notice(E_NOTICE) before PHP 8.0 and a warning(E_WARNING) after PHP 8.0.

This issue will be raised in the following cases:

• Trying to cast object to int(or integer) type.
• Trying to cast object to float or double or real type.
• Trying to cast array to string type.
• Trying to cast object to string type.
• Trying to use (unset) to cast a value to null. Casting to null has been DEPRECATED as of PHP 7.2.0, and REMOVED as of PHP 8.0.0. So relying on this feature is highly discouraged.

Bad practice

class Calc
{
    public function add(int|float $a, int|float $b): int|float
    {
        return $a + $b;
    }
}

function getValueAsInteger(Calc $calc)
{
    // invalid: $calc variable is object of class Calc which could not be converted to int
    return (int) $calc;
}

function getValueAsFloat(Calc $calc)
{
    // invalid: $calc variable is object of class Calc which could not be converted to float
    return (float) $calc;
}

function getValueAsString(Calc $calc)
{
    // invalid: $calc variable is object of class Calc which could not be converted to string
    return (string) $calc;
}

print_r(getValuesAsString([1, 2.5, 9, 100]));

function getValuesAsString(array $values)
{
    // invalid: cannot convert array to string
    return (string) $values;
}

function convertTextToNull(string $text)
{
    // invalid: avoid using unset as it is been deprecated as of PHP 7.2, and removed as of PHP 8.0
    return (unset) $text;
}

Recommended

class Calc
{
    public function add(int|float $a, int|float $b): int|float
    {
        return $a + $b;
    }
}

function getValueAsInteger(Calc $calc)
{
    /**
     * Use a method which can return valid type that can be converted to integer.
     * To find out valid type, refer to "Converting to integer" link from resources section.
     */
    return (int) $calc->getValue();
}

function getValueAsFloat(Calc $calc)
{
    /**
     * Use a method which can return valid type that can be converted to float.
     * To find out valid type, refer to "Converting to float" link from resources section.
     */
    return (float) $calc->add();
}

function getValueAsString(Calc $calc)
{
    /**
     * Use a method which can return valid type that can be converted to string.
     * To find out valid type, refer to "Converting to string" link from resources section.
     */
    return (string) $calc->add();
}

print_r(getValuesAsString([1, 2.5, 9, 100]));

function getValuesAsString(array $values)
{
    // Loop through array to cast it into string
    $result = [];
    foreach ($values as $value) {
        $result[] = (string) $value;
    }

    return $result;
}

function convertTextToNull(string $text)
{
    // avoid using (unset) cast at all
    return null;
}

References

• Type Juggling - Type Casting
• Converting to boolean
• Converting to integer
• Converting to float
• Converting to string
• Converting to object
• Converting to NULL