Syntax error: Cannot create array of lambdas in member variables

[SiebelsTim]

https://3v4l.org/Or9LN

<?hh
$x = [$x ==> $x + 1];
var_dump($x[0](1)); // outputs 2

https://3v4l.org/PLRkL

<?hh

class Test {
  private $x = [$x ==> $x + 1]; // Syntax error
}

The typechecker is fine with it, the runtime not. This doesn't work with collections either.

[jwatzman]

Weird -- thanks for the report.

[smeenai]

hh_client now gives an error for the second piece of code:

Initialization of class property must be a static literal expression. (Typing[4152])

Would it still be considered a bug in the parser, in this case?

[fredemmott]

#4277

[lexidor]

I am going over old issues on this repository, to see which ones apply to the current versions of hhvm.

The new behavior (must be a static literal expression) is valid. Hhvm does not (nor PHP) allow things that can not be known statically to appear as constant initializers. A ==> style lambda is very similar to a function() use () {} at runtime. This requires the creation of a Closure object. The [] is not required to trigger this behavior.

Footnote: The legacy Hack Collections were an exception to this rule.

class Test {
    private $q = (
        function(int $a) {
            return $a;
        }
    );
}

This code is invalid for the same reason.
PHP: PHP Fatal error: Constant expression contains invalid operations
HHVM: Fatal error: Uncaught Error: Invalid expression in constant initializer