3. a special typed value can't be casted to anything. -- this is not true, NULLs can be casted to anything (it becomes 0, "", array() ) and even resources can be casted to anything with dubious utility value.
4. casting should mention the intval() , strval() , doubleval() functions
1. "they all inherit from stdClass" -- this is simply not true
2. callables should've mentioned anonymous functions
3. a special typed value can't be casted to anything. -- this is not true, NULLs can be casted to anything (it becomes 0, "", array() ) and even resources can be casted to anything with dubious utility value.
4. casting should mention the intval() , strval() , doubleval() functions
5. php does not support explicit type definition in variable declaration -- PHP 7.4 however supports typed properties. https://wiki.php.net/rfc/typed_properties_v2