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digitalmars.D - Article: Alternatives to C++

reply Istvan Dobos <not.disclosing.here example.com> writes:
https://caiorss.github.io/C-Cpp-Notes/cpp-alternatives.html

Some good ol' C++ bashing. I found this interesting: if a 
polymorphic type gets passed by value, it loses its polymorphism. 
I haven't seen it spelled out like this before, but makes sense. 
Why mentioning it specifically though?

D is mentioned first in the General purpose section, along with 
some interesting choices (like ATS).
 From a first couple skims, there are probably a few inaccuracies 
about all of them. But I liked the linked videos section and it's 
quite nice that somebody made it into an easily readable summary.
Mar 08 2021
parent reply =?UTF-8?Q?Ali_=c3=87ehreli?= <acehreli yahoo.com> writes:
On 3/8/21 10:31 AM, Istvan Dobos wrote:


 https://caiorss.github.io/C-Cpp-Notes/cpp-alternatives.html

 Some good ol' C++ bashing. I found this interesting: if a polymorphic
 type gets passed by value, it loses its polymorphism. I haven't seen it
 spelled out like this before, but makes sense. Why mentioning it
 specifically though?


I may be responsible for that specific poing because the article lists 
my C++Now 2017 presentation as a reference where I mentioned reference 
types as a D objection at this moment in the presentation:

   https://youtu.be/vYEKEIpM2zo?t=3084

I remember Atila and others being surprised that I thought reference 
types were a D objection of C++ programmers. Here is the story why I 
thought C++ programmers may have that objection:

I co-organized and attended a presentation by Sean Parent at the Silicon 
Valley Chapter of the ACCU. Sean Parent lists multiple "ACCU" 
presentations below, so I can't be sure exactly which one that was:

   https://sean-parent.stlab.cc/papers-and-presentations/

I remember Andrei Alexandrescu and other C++ people were in the audience 
as well.

I may not remember this accurately but final slides of Sean Parent's 
presentation included his ambitions on writing a framework where he was 
hoping to be able to define the transitions of the code beforehand like 
state transitions. That made sense considering the first part of his 
presentation where he was advocating removing explicit language 
constructs like loops from the code. (This idea has been popularized by 
his famous "that's rotate" words, which has been referenced by other 
presenters as well.)

Seeing how difficult his ambitions would be achievable in C++ of that 
time, I approached him at the end of the presentation and said "Have you 
considered D? Because what you're trying to do...". I couldn't finish my 
sentence because he said "A language with reference types? No thanks!" 
while using a hand gesture that looked like "brushing away", and walked 
away.

Looking back after all these years, I think his objection might have 
been to garbage collectors. I don't know. But I never forgot that 
interaction and used that point in multiple presentations that C++ 
indeed has reference types of the worst kind: by programmer education 
through guidelines. D wins over C++ here as well by providing both 
reference types and value types. My only regret is the space cost of the 
monitor pointer of all D class objects. So, I hereby help populatize 
something I learned recently: extern(C++) class definitions don't have 
that monitor pointer:

// Smaller object:
extern (C++) class C {
   // ...
}

Anyway... This is the first time I told that story publicly. :)

Ali
Mar 08 2021
next sibling parent tsbockman <thomas.bockman gmail.com> writes:
On Monday, 8 March 2021 at 21:00:47 UTC, Ali Çehreli wrote:

 On 3/8/21 10:31 AM, Istvan Dobos wrote:


 https://caiorss.github.io/C-Cpp-Notes/cpp-alternatives.html

 Some good ol' C++ bashing. I found this interesting: if a


 polymorphic

 type gets passed by value, it loses its polymorphism. I


 haven't seen it

 spelled out like this before, but makes sense. Why mentioning


 it

 specifically though?


 I may be responsible for that specific poing because the 
 article lists my C++Now 2017 presentation as a reference where 
 I mentioned reference types as a D objection at this moment in 
 the presentation:

   https://youtu.be/vYEKEIpM2zo?t=3084

 I remember Atila and others being surprised that I thought 
 reference types were a D objection of C++ programmers.


As someone who is trying to write a reference counting system at 
the moment, reference types are a massive pain.

Class instances exist, and are semantically entirely distinct 
entities from the references to them. Being forbidden to name or 
otherwise represent the type of a class instance, and therefore 
forbidden to introspect it properly, sucks. Having to 
special-case classes and interfaces everywhere, because they are 
accessed at a different level of indirection, sucks.

D's powerful meta-programming capabilities allow me to work 
around most of these issues, but I shouldn't have to. Passing 
class instances by reference is a best practice that applies most 
of the time, not a fundamental truth that should be enforced by 
the language.
Mar 08 2021
prev sibling next sibling parent tsbockman <thomas.bockman gmail.com> writes:
On Monday, 8 March 2021 at 21:00:47 UTC, Ali Çehreli wrote:

 My only regret is the space cost of the monitor pointer of all 
 D class objects. So, I hereby help populatize something I 
 learned recently: extern(C++) class definitions don't have that 
 monitor pointer:

 // Smaller object:
 extern (C++) class C {
   // ...
 }


I think this critical bug I discovered today needs to be fixed 
before that's a good idea: dynamic casts seem to be completely 
broken for extern(C++) classes.
     https://issues.dlang.org/show_bug.cgi?id=21690
This can manifest as a logic error, memory corruption, or a 
security vulnerability depending on the circumstances.

More mundanely, extern(C++) mangling can't distinguish some 
overloads that extern(D) can. Thankfully, this problem can be 
worked around in an easy (albeit ugly) way:

     extern(C++) class C { extern(D):
         // ...
     }

In particular, I found the above necessary to enable overloading 
on `shared` with extern(C++) class methods.
Mar 08 2021
prev sibling next sibling parent reply tsbockman <thomas.bockman gmail.com> writes:
On Monday, 8 March 2021 at 21:00:47 UTC, Ali Çehreli wrote:

 So, I hereby help populatize something I learned recently: 
 extern(C++) class definitions don't have that monitor pointer:

 // Smaller object:
 extern (C++) class C {
   // ...
 }


So, it turns out that I actually found TWO critical, 
show-stopping bugs in extern(C++) class support today (thanks 
 kinke):

"Unable to dynamic cast extern(C++) classes":
     https://issues.dlang.org/show_bug.cgi?id=21690
"extern(C++) class instance dtors are never called, breaking 
RAII":
     https://issues.dlang.org/show_bug.cgi?id=21693

I believe extern(C++) classes need more testing before they 
should be recommended solely as a means to save one pointer's 
worth of memory...

I need them to work for other reasons, though, so I hope these 
get fixed.
Mar 08 2021
parent reply =?UTF-8?Q?Ali_=c3=87ehreli?= <acehreli yahoo.com> writes:
On 3/8/21 4:02 PM, tsbockman wrote:


 So, it turns out that I actually found TWO critical, show-stopping bugs
 in extern(C++) class support today (thanks  kinke):


I am happy to be involved in exposing bugs by being under-informed. :)

Once, I used the following construct during a presentation thinking that 
it would grab both locks:

   synchronized(a, b) {
     // ...
   }

Steven Schveighoffer corrected me during the presentation and later 
worked on crippling the comma operator in D. :)

Ali
Mar 08 2021
parent tsbockman <thomas.bockman gmail.com> writes:
On Tuesday, 9 March 2021 at 01:43:25 UTC, Ali Çehreli wrote:

 On 3/8/21 4:02 PM, tsbockman wrote:


 So, it turns out that I actually found TWO critical,


 show-stopping bugs

 in extern(C++) class support today (thanks  kinke):


 I am happy to be involved in exposing bugs by being 
 under-informed. :)


Well, it was a good idea - it *should* work - it just turns out 
that it doesn't, at the moment...
Mar 09 2021
prev sibling parent Istvan Dobos <not.disclosing.here example.com> writes:
On Monday, 8 March 2021 at 21:00:47 UTC, Ali Çehreli wrote:


 Anyway... This is the first time I told that story publicly. :)

 Ali


And I'm happy you did, Ali! Love reading folklore from the 
"Native Tribe" (or any tribe for that matter) :)
Mar 09 2021