constant references

[Zytan]

Re: constant references

Brian,

Even in C++ const didn't guarantee much since the reference's
constness could be casted away.

No. It guarantees a LOT. I use it regularly on large projects. It
helps enforce design issues where certain elements of my code just
should not be allowed to mess with certain data. It is extremely
important. Also, for all the elsewhere mentioned reasons in another
post of mine, such as catching bugs at compile time, make it
priceless. It just forces good programming. How can you beat that?

Yes, you can cast it away -- but not with 'normal' C++ code. Casting
away const is not allowed. You can get around it with fancy C++ code
to trick the compiler into accessing that memory, but it's really just
a high level way of writing assembly. So, yes, it's not 100% bullet
proof. But, that's not the point. The point is the immense gain you
get, from being forced to write good code, from using it.

Just because someone can pick a lock, it doesn't mean you should stop
locking your door. Now imagine a lock that forces the door to be
locked, and forces you to have the keys on you, every time you leave.
Anything that forces good habits is a good idea.

I think it was left out of C# because
the cost versus benefit of it tipped toward the unfavorable
direction. Implementing const reference parameters would add a
substantial amount of complexity to the language.

Really? I don't really know. It's just sad that it doesn't exist...

The best way to guarantee that an object's state cannot be changed is
to make it immutable.

Ok. Something else for me to learn. Any places I can get started on
researching this? Any help is appreciated.

Another strategy would be to use an interface or proxy object.
Though, I don't think either could absolutely be enforced at compile
time. A proxy object would probably be the best of two.

Thanks for the suggestion. This was mentioned above, and for
something where it is critical (i.e. it warrants the extra hassle
involved), it certainly could be used.

Zytan

[Stephany Young]

Re: constant references

Well, all I can really say is ...

If you need the features exposed by the C++ language and the C++ compiler so
badly then I don't understand why you are not using that instead of bleating
on about something that just "ain't gonna happen".


"Zytan" <zytanlithium@y ahoo.comwrote in message
news:1170438311 .677183.232900@ a34g2000cwb.goo glegroups.com.. .

Stephany,
>

>Yes you're absolutely right - the best of us do make mistakes.
>>
>That is why we have robust debugging and testing techniques.

>
Yes.
>

>Checking that some variable that shouldn't be modified hasn't been is the
>most the most basic of those techniques.

>
No. Leaving such a simple, laborious task to the compiler is one of
the basic of those techniques.
>
No human can possibly read code like English, and look over a function
in a swift manner, and determine that the constant variables are
unchanging. What happens if one of them is passed to another
function? You have to either look at that function's code, and all
it's inner function calls, all the way down the stack / tree, and
then, if you haven't missed anything (and, since when is any human
perfect), you can determine that the code is correct. If you're
incorrect, hopefully you'll catch the bug during runtime development
and not after deployment, where it's 100 times more costly to fix than
during runtime development.
>
OR... you could use "const" -- 5 letters -- and let the compiler
notify you during COMPILE time which is 1/10th as costly as catching
it during beta testing. The compiler can go through all your code,
and determine at all levels that the variable is not being changed.
You can create "const" class functions to ensure the class data
members remain unchanged, and these are only allowed to be call other
functions that promise the same thing. All caught at compile time.
>
This is several ORDERS OF MAGNITUDE more robust than "human checking".
>
Besides, who has time to check code? Who does this? Even if you
*could* check all that code, and were as perfect as a machine, why
would you want to waste your time doing this? The time would be
better spend writing more robust code, letting the compiler check all
of that for you, removing any worries / intellectual barriers that you
may have about potential broken code.
>
Zytan
>

[Brian Gideon]

Re: constant references

On Feb 2, 11:58 am, "Zytan" <zytanlith...@y ahoo.comwrote:

Brian,
>

Even in C++ const didn't guarantee much since the reference's
constness could be casted away.

>
No. It guarantees a LOT. I use it regularly on large projects. It
helps enforce design issues where certain elements of my code just
should not be allowed to mess with certain data. It is extremely
important. Also, for all the elsewhere mentioned reasons in another
post of mine, such as catching bugs at compile time, make it
priceless. It just forces good programming. How can you beat that?
>
Yes, you can cast it away -- but not with 'normal' C++ code. Casting
away const is not allowed. You can get around it with fancy C++ code
to trick the compiler into accessing that memory, but it's really just
a high level way of writing assembly. So, yes, it's not 100% bullet
proof. But, that's not the point. The point is the immense gain you
get, from being forced to write good code, from using it.
>
Just because someone can pick a lock, it doesn't mean you should stop
locking your door. Now imagine a lock that forces the door to be
locked, and forces you to have the keys on you, every time you leave.
Anything that forces good habits is a good idea.
>

Yes, you're right. I may have been a little overzealous on my point.
At the very least const adds metadata that would let the caller know
that the method claims to not modify the state of the parameter. It's
up to the developer of that method to comply with what's advertised in
the metadata.

I think it was left out of C# because
the cost versus benefit of it tipped toward the unfavorable
direction. Implementing const reference parameters would add a
substantial amount of complexity to the language.

>
Really? I don't really know. It's just sad that it doesn't exist...

That doesn't necessarily mean it won't be added in the future. But, I
suspect the chances are not good for C# and even worse for VB.

>

The best way to guarantee that an object's state cannot be changed is
to make it immutable.

>
Ok. Something else for me to learn. Any places I can get started on
researching this? Any help is appreciated.
>

It's not a particularly clever concept or anything. All you do is
make sure the methods on a class have no side-effects to the object
from which they are called. The String data type is an example of an
immutable class.

Another strategy would be to use an interface or proxy object.
Though, I don't think either could absolutely be enforced at compile
time. A proxy object would probably be the best of two.

>
Thanks for the suggestion. This was mentioned above, and for
something where it is critical (i.e. it warrants the extra hassle
involved), it certainly could be used.

It's partially related to mutability. The difference with the proxy
object is that the real object is mutable, but the proxy is not. Like
you said, it's not something you're going to want to create for every
class.

[Zytan]

Re: constant references

If you need the features exposed by the C++ language and the C++ compiler so

badly then I don't understand why you are not using that instead of bleating
on about something that just "ain't gonna happen".

Stephany, This isn't a VB vs. C++ issue. It's language independent.
This is off topic.

Zytan

[Zytan]

Re: constant references

Brian,

Thanks again for your reply.

Yes, you're right. I may have been a little overzealous on my point.
At the very least const adds metadata that would let the caller know
that the method claims to not modify the state of the parameter. It's
up to the developer of that method to comply with what's advertised in
the metadata.

Yup, it's a godsend. I didn't realize its power until I started
making use of it. I imagine most people haven't experienced this, and
they probably think I am crazy since "if you don't want anything to
change the data, just make sure your code doesn't change it." When I
first implemented it, and it forced me to refactor about 50 functions,
some of them being major refactors, I realized it was helping me
maintain blackbox / encapsulation style programming. I was like,
"Wow." But, almost no code I see makes use of it, even professional
code...

That doesn't necessarily mean it won't be added in the future. But, I
suspect the chances are not good for C# and even worse for VB.

I imagine you are right. If no one cares... why implement it? They
have new .NET functionality to write, after all. Time is limited.

It's not a particularly clever concept or anything. All you do is
make sure the methods on a class have no side-effects to the object
from which they are called. The String data type is an example of an
immutable class.

Aaaah. I see.

Thanks for your time -- everybody -- it is appreciated.

Zytan

[Herfried K. Wagner [MVP]]

Re: constant references

<lord.zoltar@gm ail.comschrieb:

>Are they possible? I am passing in a large array of Bytes, thus I
>don't want to use ByVal.

>
Have you tried using ByRef? Look up passing variables ByRef for
VB .NET.

This would even be dangerous because it allows the method to change the
reference passed to the method in the parameter! 'ByVal' and 'ByRef' are
not really related to the OP's problem, although 'ByVal' is much more
appropriate here.

--
M S Herfried K. Wagner
M V P <URL:http://dotnet.mvps.org/>
V B <URL:http://dotnet.mvps.org/dotnet/faqs/>

[Herfried K. Wagner [MVP]]

Re: constant references

"Stephany Young" <noone@localhos tschrieb:

Well, all I can really say is ...
>
If you need the features exposed by the C++ language and the C++ compiler
so badly then I don't understand why you are not using that instead of
bleating on about something that just "ain't gonna happen".

Hm... I think it's interesting that someone shows his/her interest in
functionality similar to 'const'. I believe that adding a similar concept
to .NET has been considered, but maybe it's worth to reconsider it.

--
M S Herfried K. Wagner
M V P <URL:http://dotnet.mvps.org/>
V B <URL:http://dotnet.mvps.org/dotnet/faqs/>

[Stephany Young]

Re: constant references

You get no argument from me on that count Herfried.

I was responding to the OP's rant that basically was saying that VB.NET was
unusable because it didn't have this particular 'feature' and that it had to
be 'fixed' immediately.

I have no problem at all about a debate on whether or not such a concept
should or shouldn't be included in a future relase of the language.


"Herfried K. Wagner [MVP]" <hirf-spam-me-here@gmx.atwrot e in message
news:%23WhLb0xR HHA.488@TK2MSFT NGP06.phx.gbl.. .

"Stephany Young" <noone@localhos tschrieb:

>Well, all I can really say is ...
>>
>If you need the features exposed by the C++ language and the C++ compiler
>so badly then I don't understand why you are not using that instead of
>bleating on about something that just "ain't gonna happen".

>
Hm... I think it's interesting that someone shows his/her interest in
functionality similar to 'const'. I believe that adding a similar concept
to .NET has been considered, but maybe it's worth to reconsider it.
>
--
M S Herfried K. Wagner
M V P <URL:http://dotnet.mvps.org/>
V B <URL:http://dotnet.mvps.org/dotnet/faqs/>

[Cor Ligthert [MVP]]

Re: constant references

Zytan,

Before I wrote this I have looked at the calendar, and it is really 2007.

I thought that I was back in 1967 while I was reading your response.

Although I agree with you in concept is it now much to late start again a
discussion.

As the Arabs had than won the Arab-Isrealy war, than a lot of things would
probably look different now, however you cannot change history (beside in
the schoolbooks of course).

Cor

"Zytan" <zytanlithium@y ahoo.comschreef in bericht
news:1170438311 .677183.232900@ a34g2000cwb.goo glegroups.com.. .

Stephany,
>

>Yes you're absolutely right - the best of us do make mistakes.
>>
>That is why we have robust debugging and testing techniques.

>
Yes.
>

>Checking that some variable that shouldn't be modified hasn't been is the
>most the most basic of those techniques.

>
No. Leaving such a simple, laborious task to the compiler is one of
the basic of those techniques.
>
No human can possibly read code like English, and look over a function
in a swift manner, and determine that the constant variables are
unchanging. What happens if one of them is passed to another
function? You have to either look at that function's code, and all
it's inner function calls, all the way down the stack / tree, and
then, if you haven't missed anything (and, since when is any human
perfect), you can determine that the code is correct. If you're
incorrect, hopefully you'll catch the bug during runtime development
and not after deployment, where it's 100 times more costly to fix than
during runtime development.
>
OR... you could use "const" -- 5 letters -- and let the compiler
notify you during COMPILE time which is 1/10th as costly as catching
it during beta testing. The compiler can go through all your code,
and determine at all levels that the variable is not being changed.
You can create "const" class functions to ensure the class data
members remain unchanged, and these are only allowed to be call other
functions that promise the same thing. All caught at compile time.
>
This is several ORDERS OF MAGNITUDE more robust than "human checking".
>
Besides, who has time to check code? Who does this? Even if you
*could* check all that code, and were as perfect as a machine, why
would you want to waste your time doing this? The time would be
better spend writing more robust code, letting the compiler check all
of that for you, removing any worries / intellectual barriers that you
may have about potential broken code.
>
Zytan
>

[=?Utf-8?B?VGVycnk=?=]

Re: constant references

I know I am a little late in joining this discussion, but I was just reading
something in the documentation that may be of some help - not sure since I
have not tried it yet. New to the .Net Framework version 2 is the
"Array.AsReadOn ly" Generic Method that retrurns a read-only wrapper for the
specified array. So if you passed the original array (reference) byval, the
first line of code could be something like:
TheArray = Array.AsReadOnl y(TheArray) ' assuming the param was "TheArray"
Then it seems to me that the compiler should find and flag any attempts to
modify the array. And of course, the byval keeps the original reference from
being modified.
I am fairly new to .net myself, so maybe I am on the wrong track here, but
it sounds like it should work.
--
Terry


"Zytan" wrote:

Branco,
>
I had actually typed up a lengthy post asking about that, as well, and
Google Groups did something strange, and loaded a new page, erasing
the whole thing (one major flaw of web apps -- load a new page by
accident, and say goodbye to all your work), so I forgot about it, and
just asked the basic question.
>
I was going to ask if array variables are like C++ arrays (i.e. like
pointers), so that even if the 'pointer' is const, you can still
change what it points to (unless that is also const). All VB .NET
help files and tutorials never even touch upon these things. Very
annoying. It's like they think the programmer shouldn't be thinking
about these things...
>
Anyway... that leads to the question:
>
How can I pass in an array to a function/sub so that the entire array
is const and cannot be changed? Or should I be using C# instead for
such functionality?
>
Thanks for your reply,
>
Zytan
>
>

[Zytan]

Re: constant references

On Feb 2, 6:54 pm, "Herfried K. Wagner [MVP]" <hirf-spam-me-
h...@gmx.atwrot e:

Hm... I think it's interesting that someone shows his/her interest in
functionality similar to 'const'. I believe that adding a similar concept
to .NET has been considered, but maybe it's worth to reconsider it.

My point exactly, Herfried. My original post was how to replicate the
functionality, since VB does have "Const" in some parts of the
language. Since discovering it cannot be replicated in full, it is
certainly a legitimate point to raise concern that this feature should
be added for the numerous benefits I have mentioned. Unfortunately,
since most people have never made use of such features, even when they
are using languages that support them. So, they wouldn't really "get"
why it is so invaluable. I made effort to explain most of the major
reasons pretty clearly (there are more, such as how "const" protects
code from improper changes of OTHER programmers not-in-the-know, or
even yourself 6 months from now when you've forgotten how some
function works). But, it's hard for people to listen when they think
I am attacking their language. I am pointing out its weaknesses,
yes. This is how change begins. I do the same with all languages I
use. I guess, also, you don't miss anything you've never had. I
didn't care that all languages didn't have "const" functionality until
I used it. People here are acting like the old me. But, I listened
when someone said I should be using "const", and I started using it.
In this manner, I stumbled upon how useful it was -- I couldn't
possibly have known every benefit it brought without using it
personally (although most of them were found by listening to others).
I wish you all could share this experience. Maybe that's why
intelligent people have said programmers should learn a new language
every year... I should try that. There's probably tons of things I
am missing that I don't realize, yet.

Zytan

[Zytan]

Re: constant references

Stephany,

You get no argument from me on that count Herfried.

Herfried is agreeing with me that it is useful to considering new
language features.

I have no problem at all about a debate on whether or not such a concept
should or shouldn't be included in a future release of the language.

Now you are agreeing with me. We are currently HAVING such a debate.

I was responding to the OP's rant that basically was saying that VB.NET was
unusable because it didn't have this particular 'feature' and that it had to
be 'fixed' immediately.

I said VB .NET is unusable, and must be fixed immediately... because
it doesn't have "const"!?
Unbelievable.
My discussion with you ends now.

Zytan

[Zytan]

Re: constant references

Cor,

Before I wrote this I have looked at the calendar, and it is really 2007.
>
I thought that I was back in 1967 while I was reading your response.
>
Although I agree with you in concept is it now much to late start again a
discussion.
>
As the Arabs had than won the Arab-Isrealy war, than a lot of things would
probably look different now, however you cannot change history (beside in
the schoolbooks of course).

Thanks for the insults.

You're telling me that the... compiler... cannot do *compile time
checks* to ensure a variable is NOT changed inside of a function?

Exactly what history must be changed in order for someone to improve
the compiler?

Maybe if we all edit wikipedia, perceived history will change, and
someone will realize it is actually possible, and then someone will
improve the compiler.

Zytan

[Zytan]

Re: constant references

Terry,

I know I am a little late in joining this discussion, but I was just reading
something in the documentation that may be of some help - not sure since I
have not tried it yet. New to the .Net Framework version 2 is the
"Array.AsReadOn ly" Generic Method that returns a read-only wrapper for the
specified array. So if you passed the original array (reference) byval, the
first line of code could be something like:
TheArray = Array.AsReadOnl y(TheArray) ' assuming the param was "TheArray"
Then it seems to me that the compiler should find and flag any attempts to
modify the array. And of course, the byval keeps the original reference from
being modified.

Thanks for the reply. Branco mentioned this earlier, and he claimed
that it still would only be caught at run time. I am not sure, I'd
have to test and see. But, this is better than nothing. And it's
better than proxy objects because it is specifically designed for
this, needing much less code. I'll give it a shot.

Thanks,

Zytan

[Zytan]

Re: constant references

New to the .Net Framework version 2 is the

"Array.AsReadOn ly" Generic Method that returns a read-only wrapper for the
specified array.

This works, but note that the result is a collection. It is not
something you can just drop into existing code.

Zytan