50 Random PHP5 Facts

Here's a list of 50 49 random facts about PHP.

1. You MUST load PDO before loading any PDO drivers
2. An iterator cannot be used with foreach by reference
3. Cannot create references to elements of a temporary array expression
4. Cannot create references to/from string offsets nor overloaded objects
5. Cannot assign by reference to overloaded objects
6. Only variable references should be returned by reference
7. Only variables can be passed by reference
8. Cannot return string offsets by reference
9. Cannot use string offset as an array
10. Cannot use object as array -- See Dans comment
11. Cannot use a NULL value as an array
12. Cannot use a scalar value as an array
13. foreach() can not iterate over objects without PHP class
14. Cannot use assign-op operators with overloaded objects nor string offsets
15. __HALT_COMPILER() can only be used from the outermost scope
16. Assigning the return value of new by reference is deprecated
17. Variables passed to each() must be an array or object
18. Constants may only evaluate to scalar values
19. is_a() is deprecated. The "instanceof" operator should be used instead This has changed as of PHP 5.3, see Gregs comment
20. Cannot add internal functions to return value from get_defined_functions()
21. Cannot add user functions to return value from get_defined_functions()
22. Static functions cannot be abstract
23. Exceptions must be derived from the Exception base class
24. Need to supply an object when throwing an exception
25. Cannot declare self-referencing constants
26. Cannot use call_user_function on objects without a class entry
27. Cannot access self:: when no class scope is active
28. Cannot access parent:: when no class scope is active
29. Cannot access parent:: when current class scope has no parent
30. add_assoc_function() is no longer supported
31. Usage of {} to access string offsets is deprecated and will be removed in PHP 6
32. Cannot re-assign $this
33. __toString() must not throw an exception
34. Can't use method return value in write context
35. Can't use function return value in write context
36. Multiple access type modifiers are not allowed
37. Cannot use the final modifier on an abstract class member
38. Default value for parameters with a class type hint can only be NULL
39. Default value for parameters with array type hint can only be an array or NULL
40. Cannot call __clone() method on objects - 'clone $obj' should be used instead
41. Clone method does not require arguments
42. Interfaces cannot not implement themselves
43. Classes may not inherit from classes declared final
44. Classes cannot inherit previously-inherited constants from interfaces
45. Classes cannot implement previously-implemented interfaces
46. Class declarations may not be nested
47. Cannot use reserved words as class or interface names
48. Interfaces may not include member variables
49. Properties cannot be declared abstract
50. Cannot declare properties final, the final modifier is allowed only for methods