On Sun, 27 Sep 2009 02:49:06 +0400, Walter Bright
<[email protected]> wrote:
Denis Koroskin wrote:
On Sun, 27 Sep 2009 01:49:45 +0400, Walter Bright
<[email protected]> wrote:
The problem with non-nullable references is what do they default to?
Some "nan" object? When you use a "nan" object, what should it do?
Throw an exception?
Oh, my! You don't even know what a non-null default is!
There is a Null Object pattern
(http://en.wikipedia.org/wiki/Null_Object_pattern) - I guess that's
what you are talking about, when you mean "nan object" - but it has
little to do with non-null references.
It's the black hole object. It prevents you from getting a seg fault,
but I see no rationale for expecting that an unexpected null object
always returning "I succeeded" means your program will operate correctly.
The white hole object, of course, always throws an exception when it is
accessed. At least you know something went wrong - but you already have
that with null.
With non-null references, you don't have "wrong values", that throw an
exception upon use (although it's clearly possible), you get a correct
value.
You're not getting a correct value, you're getting another default value.
I'm sorry but I can not continue discussion with you like that. You are
not listening! You are not even trying to understand what I say. We are
talking *completely* different things here.
Who the hell cares if it's a black or white as long as it is a hole
object? I tell you that no one is gonna use it, because it's *much* easier
to do everything right (i.e. initialize a reference to proper value) than
create Hole classes for each of the class/interface. I can't even imagine
anyone writing the code like this:
T someFunction(Args someArgs) {
ISomeInterface someInterface = new
BlackHoleOfSomeInterfaceThatAlwaysThrows(); // let's initialize that
variable to some dumb value just to make compiler happy
// rest of the method body
}
Novices, maybe. But professionals would never do that sin for sure.
*Please* let's go past that pattern, it really has nothing to do with
proposed non-null by default references.
If the logic of your program is expecting a prime number > 8, and the
null object returns 0, now what?
You are talking heresy here. I'm afraid you don't even know what you are
talking about.
A) There is no such thing as null object. That's bullsh*t! No one ever
proposed to use those, you did. And now you deny use of them and discuss
how bad they are.
B) You can't call a function that accepts non-null T if you don't have a
valid (i.e. non-null) T reference. End of story.
If an object may or may not have a valid value, you mark it as
nullable. All the difference is that it's a non-default behavior,
that's it. And a user is now warned, that an object may be not
initialized.
He isn't warned, that's just the problem. The null object happily says
"I succeeded" for all input and returns more default values and null
objects.
Please stop that "null object" pattern propaganda. Did you even read what
I wrote?
I wrote: if a variable may be not initialized - no problem, make it
nullable and assign a null! A user is now forced to check that variable
against a null before dereference and must take appropriate actions if it
is null.
What happens if the output of your program then becomes a null object?
How are you going to go about tracing that back to its source? That's a
lot harder than working backwards from where a null exception originated.
I used to work at Boeing designing critical flight systems. Absolutely
the WRONG failure mode is to pretend nothing went wrong and happily
return default values and show lovely green lights on the instrument
panel. The right thing is to immediately inform the pilot that something
went wrong and INSTANTLY SHUT THE BAD SYSTEM DOWN before it does
something really, really bad, because now it is in an unknown state. The
pilot then follows the procedure he's trained to, such as engage the
backup.
A null pointer exception fits right in with that philosophy.
You could think of null exceptions like pain - sure it's unpleasant, but
people who feel no pain constantly injure themselves and don't live very
long. When I went to the dentist as a kid for the first time, he shot my
cheek full of novacaine. After the dental work, I went back to school. I
found to my amusement that if I chewed on my cheek, it didn't hurt.
Boy was I sorry about that later <g>.
That's trolling, Walter. I'm sorry, but you are talking non-sense here.
Once again, no one ever proposed use of null object pattern. You imagined
it and now denying its use.
