catch with type intersection

[rick645]

$ php -v | grep cli
PHP 8.1.2-1ubuntu2.14 (cli) (built: Aug 18 2023 11:41:11) (NTS)


$ cat catch.php
<?php
interface Err {
    function getExitCode();
}

function main(Throwable&Err $throwable1)  { #ID1
    try {
        throw $throwable1;
    } catch (Throwable&Err $throwable2) { #ID2
        echo $throwable2->getExitCode() . PHP_EOL;
    }
}

$throwable = new class extends Exception implements Err {
    function getExitCode() {
        return 123;
    }
};

main($throwable);

I highlight a few lines

$ grep ID catch.php
function main(Throwable&Err $throwable1)  { #ID1
    } catch (Throwable&Err $throwable2) { #ID2

So let's try

$ php catch.php
PHP Parse error:  syntax error, unexpected token "&", expecting ")" in /tmp/catch.php on line 10

Why?

mmmhhh...

I try to remove Throwable& from the line #ID2

$ grep ID2 catch.php
    } catch (Err $throwable2) { #ID2
$ php catch.php
123

Works!!!

So it seems that catch doesn't accept the type intersection.
Why?
Is there any official documentation that talks about it?

Edited September 8, 2023 by rick645

[kicken]

The documentation says you can combine using |. 

Quote

As of PHP 7.1.0, a catch block may specify multiple exceptions using the pipe (|) character. This is useful for when different exceptions from different class hierarchies are handled the same.

Throwable&Err is redundant anyway.  Anything that is thrown must implement throwable, so just specifying Err is all you need.

 

[requinix]

You cannot catch with type intersection - only a type union, which isn't really a union but more like a syntax meaning "or".

If you want a type intersection then use a named class. But in your case, kicken's right: all you actually care about is the Err and its getExitCode method anyway.

[rick645]

Redundant?

mmmhhh...

} catch (InvalidArgumentException&Err $throwable) {

Catches exceptions that extend InvalidArgumentException and implement Err.
Very comfortable, I would say!!!

Wouldn't it be right to propose it for a future version of php?

[requinix]

I think you're misusing inheritance and interfaces, but sure, go ahead and try the RFC process if you want.