On Saturday, 15 September 2012 at 10:58:07 UTC, Jonathan M Davis
wrote:
Classes are polymorphic. They have inheritance and virtual
functions.
Polymorphism makes no sense with a variable on the stack.
Having inheritance
with objects on the stack risks object slicing (
http://en.wikipedia.org/wiki/Object_slicing ). Sure, you _can_
have a
polymorphic object which is on the stack (which is why C++
allows classes on
the stack and why D has std.typecons.scoped), but it's the sort
of thing that
tends to be begging for bugs.
The designers of D decided that it's was cleaner and safer to
separate objects
which were meant to be polymorphic and those which were meant
to be non-
polymorphic (as is often considered best practice in C++), and
since having
polymorphic objects means that you're not using their
polymorphism and having
them on the stack can be dangerous, it was decided to follow
Java and C#'s
example and make all classes into reference types which live on
the heap
(though unlike Java and C#, we _can_ put such objects on the
stack if we
really want to via std.typecons.scoped). But unlike Java and
C#, we have
structs which are full-on objects with constructors and
destructors and are
the same in classes in pretty much every way except that they
have no
polymorphism and normally go on the stack.
The result is safer than what C++ has but is still very
powerful. And since
it's arguably best practice not to put objects which are meant
to use
polymorphism on the stack in C++ anyway, it's not even really
restricting you
from much in comparison to C++ (and std.typecons.scoped makes
it possible to
put classes on the stack if you really want to, making the
restrictions even
less).
You can like it or not, but separating structs and classes and
making classes
reference types on the heap is a design decision based on the
best practices
and common bugs in C++. And it works very well. Upon occasion,
it can be
limiting (hence why we have std.typecons.scoped), but I don't
think that
you're going to find very many D programmers who think that the
separation of
structs and classes was a bad idea.
You should keep in mind that D's general philosophy is to make
the defaults
safe but to allow you to do more powerful, dangerous stuff when
you need to.
The result is that it's just as powerful as C++ when you need
it to be but
that it's a lot safer in general, meaning that you're going to
have fewer bugs
in your code.
A prime example of this is the fact that all variables are
default-
initialized. This way, you never have problems with variables
being
initialized to garbage, which can cause non-deterministic,
hard-to-track-down
bugs. But if you really need the extra speed of a variable not
being
initialized when it's declared, then you can initialize it to
void. e.g.
int i = void;
This makes it so that code is far less error-prone in general
while still
allowing you to have the same down to the metal speed that
C/C++ offers when
you really need it. And it's that philosophy which governs a
lot of D's
features.
- Jonathan M Davis
I have SO MANY issues with the above statements I wouldnt know
where to start.
I have been attempting to raise these (and many related) issues
before.
Firstly, responding in particular to Jonathan M Davis (albeit
rather late),
I concede your comments are made in good faith and are even
ACCURATE.
My problem is that they are INSUFFICIENT.
I haven't announced to regular viewers that I STARTED these
issues by writing direct to Walter (twice) that I had some
language extension IDEAS I thought would be VALUABLE to ALL. Such
Ideas would make a welcome addition to ANY language but for me D
comes closest.
(A C like language with NO header files alone is worth 50%).
Naturally all he could really do was to send me along to the
forums.
However, I can see that if I am to receive the usual polite
refusal,
and I really wish to make a POINT I'd better be armed.
I would need to be able to speak your language (learn D)
before I should expect you to speak mine (implement My Ideas).
I can see here that my best bet is to learn D.
Can one learn it all online? What is the best D book?
