Catchable fatal error Argument 1 passed to ClassA method a must be an instance of ClassB instance of ClassWrong given

Question

I am trying to implement Type Hinting of PHP5 on one of my class,

class ClassA {
    public function method_a (ClassB $b)
    {}
}

class ClassB {}
class ClassWrong{}

Correct usage:

$a = new ClassA;
$a->method_a(new ClassB);

producing error:

$a = new ClassA;
$a->method_a(new ClassWrong);

Catchable fatal error: Argument 1 passed to ClassA::method_a() must be an instance of ClassB, instance of ClassWrong given...

Is it possible to catch that error(since it says "catchable")? and if yes, how?

Answer 1

Hello @kartik,

This is not a catchable fatal error anymore in php 7. Instead an "exception" is thrown. An "exception" (in scare quotes) that is not derived from Exception but Error; it's still a Throwable and can be handled with a normal try-catch block. 

E.g.

<?php
class ClassA {
  public function method_a (ClassB $b) { echo 'method_a: ', get_class($b), PHP_EOL; }
}
class ClassWrong{}
class ClassB{}
class ClassC extends ClassB {}


foreach( array('ClassA', 'ClassWrong', 'ClassB', 'ClassC') as $cn ) {
    try{
      $a = new ClassA;
      $a->method_a(new $cn);
    }
    catch(Error $err) {
      echo "catched: ", $err->getMessage(), PHP_EOL;
    }
}
echo 'done.';

prints

catched: Argument 1 passed to ClassA::method_a() must be an instance of ClassB, instance of ClassA given, called in [...]
catched: Argument 1 passed to ClassA::method_a() must be an instance of ClassB, instance of ClassWrong given, called in [...]
method_a: ClassB
method_a: ClassC
done.

Hope it helps!!

Thank You!!