On 01/21/2011 03:51 PM, Don wrote:
Don wrote:
BlazingWhitester wrote:
I spotted some patents that can theaten current DMD implementation.
Wanted to clarify things.
http://www.freepatentsonline.com/6185728.pdf - this patent describes
method pointers implementation (delegates)
This was obviously a patent aimed at protecting Delphi from VB. It's
all about the RAD designer: visual connections between GUI elements
and events has a 1:1 correspondence with code; delegates are used to
achieve this.
D delegates can store a data pointer to a nested function, or to an
object. This is rather more general (not an object-oriented feature),
and doesn't provide a 1:1 correspondence to visuals.
I presume they were only able to satisfy the requirements for novelty
and non-obviousness, because of the RAD usage. In fact, there doesn't
seem to be any suggestion that delegates would be used for anything else.
The more general idea of storing a data pointer and a function pointer
together is simple and obvious, and surely has prior art.
D's delegate scheme is essentially the same as described by Richard
Hickey, "C++ report" (Feb 1995).
See also a discussion on comp.std.c++, Feb 1996, titled "Generic Object
Callbacks". Ian Willmott states:
"I suggest that a new data type needs to be added to the language. We
could call it "pointer-to-bound-member-function".
...
Conceptually, it is a two-element structure consisting of
pointer into data space, identifying an object, and a pointer into
code space, identifying a member function on that object. The static
type of such a variable is the signature (return type and arguments)
of the member functions it is compatible with, just as the type of a
regular function pointer is the signature of the functions it can
reference. The only operations defined for this type are assignment,
equality, and callthrough. Static typechecking is done at the point
where a value of this type is created, and where a call is made
through it. "
Borland's patent dates from Feb 6, 2001. They were SIX YEARS too late.
<g>
IIUC, the structure you describe is /exactly/ the same, both concretely
and semantically as Oberon-2 "type-bound procedures" (read: virtual
methods). Oberon-2 was created in 1991, IIRC. This makes 10 years ;-)
Unlike you, I don't consider D's delegate to follow the same scheme.
Sure, it's a pair of pointers, one of which point to a routine (to use a
neutral word). But in the case of D the second one does not point to to
a type/object, but to the definition scope (environment). This is very
different, isn't it?
Thus I would consider D to not even be concerned by the patent. If you
use a 3-integer struct to store a color, do you have to pay royalties to
the owner of a patent about a 3-integer struct used to store a position?
Indeed, lawyers...
Denis
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