In Rust, generic code is fully validated as it should be, with all trait bounds being matched where need be. So you would rarely end up with needing to figure (at compile time) whether generic type T is an enum or not - because it wouldn't allow you to do anything extra with it out of the box. In Rust, an idiomatic way of adding different behaviours based on the kind of the generic type would be using traits still - e.g., you can have multiple impl blocks on your generic type, each one having different trait bounds on the generic parameter, like - if T: Copy, then implement these extra methods; standard library has tons of examples like this. The only exception that comes to mind is proc macros - when you deal with Rust code in AST form and generate new code at pre-compile-time phase, but that's a completely different story and not really related.
Indeed Rust proc macros, or Rust macros in general, are a better analog to C++ templates than Rust generics. They aren't quite the same, as during evaluation time C++ can do a bit more, and apparently type_traits is an example of what C++ can do statically. Rust's model is different, it wants macro expansion to be done by the time it starts even resolving any non-macro paths, let alone type checking or anything.
That being said, you'll be able to emulate something like that once specialization lands (hopefully also included by min_specialization).
Mind you it probably has very little real world usage right now..
Concepts aren't as powerful as Rust traits in that they are static dispatch only, while Rust supports both static & dynamic-- but they should make for cleaner code than <type_traits>
"Object-oriented programming: Some history, and challenges for the next fifty years"
https://www.sciencedirect.com/science/article/pii/S089054011...
Than read on BETA design for example,
Follow up with "The Art of the Metaobject Protocol",
https://mitpress.mit.edu/books/art-metaobject-protocol
and "Xerox LOOPS"
http://www.softwarepreservation.org/projects/LISP/interlisp_...
Then "Component Software: Beyond Object-Oriented Programming" (the 1st edition with Component Pascal)
https://www.amazon.com/Component-Software-Beyond-Object-Orie...
"Applying Traits to the Smalltalk Collection Classes"
https://rmod.inria.fr/archives/papers/Blac03a-OOSPLA03-Trait...
"Self – The Power of Simplicity"
http://media.cichon.com/talks/Introduction_Self_Language_OOP...
https://blog.rfox.eu/en/Programming/Series_about_Self/index....
How about this for starters?
https://news.ycombinator.com/item?id=11940050
On Understanding Data Abstraction Revisited
https://www.cs.utexas.edu/~wcook/Drafts/2009/essay.pdf
The Power of Interoperability: why objects are inevitable
https://www.cs.cmu.edu/~aldrich/papers/objects-essay.pdf
A closure is a poor man's object
http://people.csail.mit.edu/gregs/ll1-discuss-archive-html/m...
This isn't knocking the book, I've read it and agree that it's edifying. This list is a good resource on OOP in general. It's just not helpful in the context of this thread.
Your own words, documentation and knowledge was shared, apparently you are the one not interested.
Again: Does one really, concretely, have to read The Art of the Metaobject Protocol, a book about Lisp, to evaluate this claim about C++? Having read the book, I would say no. Which is why I say that you are evading a real discussion.
(And for that matter, it would be interesting if you fleshed out your counter-claim -- "Other than the classes used to implement all those STL concepts." -- in a bit more detail. Are you saying that all uses of C++ classes are OOP? Or that only certain uses are, but that the way classes are used to implement the STL fall into this category? Will I find the answer to these concrete questions in The Art of the Metaobject Protocol?)
Definitely, any use of class constructs with data members and member functions is OOP.
Any use of data members inside class constructs represents aggregation and if any member function on a data member happens to be called, as means to help a member function to do their work, that is delegation.
Any template implemented as class that uses its type parameters to decide at compile time what gets called, makes use of dynamic dispatch decided at compile time.
If you prefer we can pick any random STL type and dissect all their uses of OOP features, lets start with something like std::set?
Definitely not.
OOP requires, also, runtime binding and polymorphism. You can get the polymorphism by inheritance, delegation, or what-have-you. You can get runtime binding with a vtable or a name lookup.
The usual term for just-encapsulation is "object-based". The STL is definitively not object-oriented, according to its author, Stepanov, who has said that giving the STL classes member functions was a mistake.
OOP is a niche technique. It has uses, sometimes. More often, a function pointer suffices.
Object based languages are part of the OOP universe from CS point of view, plenty of literature, that apparently is too much to ask to read about, some of which I have provided above.
So here we go about std::set and it being OOP.
1 - class set, a means for encapsulation, with most of its members de
2 - Uses delegation for memory allocation via the allocator_type
3 - Uses delegation for key lookups and value comparisasion
4 - Implements the concepts Container, AllocatorAwareContainer, AssociativeContainer, ReversibleContainer alongside their respective concept dependencies, which in OOP speak are protocols/traits/categories;
5 - The actual types used for comparisaion and allocation are instances of the respective protocols, with dispatch being decided at compilation time of std::set uses, given the respective implementations as type parameters, in a way similar to multi-method-dispatch.
As bonus here is a simplified UML diagram. It isn't more detailed, because my patience to draw ASCII art is limited.
-------------------------------------------------------------------------------------------
|std| |
----- |
| __________________ |
| | <<protocol>> | |
| | Container | |
| |-----------------| |
| |-----------------| |
| |-----------------| |
| | constructor | |
| | copy-constructor| |
| | destructor | |
| | begin() | |
| | end() | |
| | cbegin() | |
| | cend() | |
| | swap() | |
| | size() | |
| | max_size() | |
| | empty() | |
| ------------------- |
| /\ |
| -- |
| | extends |
| | |
| ______________ _______________________ _______________________ |
| | <<protocol>>| | <<protocol>> | | <<protocol>> | |
| | Allocator | | ReversibleContainer | | AssociativeContainer | |
| |-------------| |----------------------| |----------------------| |
| |-------------| |----------------------| |----------------------| |
| | constructor | | rbegin() | | key_comp() | |
| | destructor | | rend() | | value_comp() | |
| | allocate | | crbegin() | |----------------------| |
| | deallocate | | crend() | /\ |
| | max_size | |----------------------- -- |
| | construct | /\ | |
| | destroy | -- implements | |
| --------------- | | |
| /\ | | |
| -- | implements / |
| | \ / |
| | implements \ / |
| | \ / |
| | \------------------ |
| | | |
| | | |
| | ------------------ |
| ---------------- | <<protocol>> | |
| | allocator<T> | uses | set | |
| |---------------|<------------------------/\|------------------| |
| |---------------| \/| constructor | |
| | destructor | |
| | begin() | |
| | end() | |
| | cbegin() | |
| | cend() | |
| | rbegin() | |
| | rend() | |
| | crbegin() | |
| | crend() | |
| | operator= | |
| | get_allocator() | |
| | empty() | |
| | size() | |
| | max_size() | |
| | clear() | |
| | insert() | |
| | emplace() | |
| | emplace_hint() | |
| | erase() | |
| | swap() | |
| | extract() | |
| | merge() | |
| | count() | |
| | find() | |
| | contains() | |
| | equal_range() | |
| | lower_bound() | |
| | upper_bound() | |
| | key_comp() | |
| | value_comp() | |
| ------------------ |
|-----------------------------------------------------------------------------------------|Concretely, you cannot take a Container pointer and point it at a std::set. You can take a T, and bind T to std::set at compile time; but that is Generic Programming: analogous, in some ways, but not the same.
In the '90s it was fightin' words to say "X is not Object Oriented", because Object-Oriented was taken as a high-status way to say Good, and "Not Object-Oriented" translated implicitly to "Not Good".
But in our brave new world, object-oriented is but one design discipline, and we have others, and enough language primitives to construct our own disciplines by mix-and-match as problems dictate.
And, I have myself simplified code that had used a virtual function to use, instead, a function pointer, and it was (still) Good. Better, even.
What renowned SIGPLAN or IEEE paper states that runtime binding is required for 100% of all OOP programming languages ever created and polymorphic dispatch at compile time doesn't count?
Changing the definition would be moving the goalposts. A new definition deserves a new word.
I mean... in the sense in which most people use "OO language" (which is, "a language with constructs which associates a data specification with procedures"), yes. Only hardcore pure-functional algorithms written in Haskell / ML without typeclasses, or things like Prolog, Esterel (though thinking about it), and similar research languages aren't.
Once upon a time programming looked like this. https://github.com/chrislgarry/Apollo-11/blob/master/Luminar...
Plenty of SIGPLAN papers to one educate themselves about what OOP is all about.
OOP is not MFC alone, apparently those that learn languages on the trenches without referring to them, never get to appreciate the wealth of information we have available.
Not surprising, given how many misunderstand "whatever my compiler does" for what ISO actually says.
Back to STL, it makes heavy use at compile time method dispatch via template metaprogramming and lambdas (which are implemented as classes actually by the compiler.
I know this is an argumentum ab auctoritate, but you didn't really provide an argument either :)
> Yes. STL is not object oriented. I think that object orientedness is almost as much of a hoax as Artificial Intelligence. I have yet to see an interesting piece of code that comes from these OO people. In a sense, I am unfair to AI: I learned a lot of stuff from the MIT AI Lab crowd, they have done some really fundamental work: Bill Gosper's Hakmem is one of the best things for a programmer to read. AI might not have had a serious foundation, but it produced Gosper and Stallman (Emacs), Moses (Macsyma) and Sussman (Scheme, together with Guy Steele). I find OOP technically unsound. It attempts to decompose the world in terms of interfaces that vary on a single type. To deal with the real problems you need multisorted algebras - families of interfaces that span multiple types. I find OOP philosophically unsound. It claims that everything is an object. Even if it is true it is not very interesting - saying that everything is an object is saying nothing at all. I find OOP methodologically wrong. It starts with classes. It is as if mathematicians would start with axioms. You do not start with axioms - you start with proofs. Only when you have found a bunch of related proofs, can you come up with axioms. You end with axioms. The same thing is true in programming: you have to start with interesting algorithms. Only when you understand them well, can you come up with an interface that will let them work.
I have seen this a few times and have felt that "hoax" is the wrong word each time. Later he talks about OOP being "philosophically unsound", which adds some clarity to the statement. It's not that OOP or AI are made up (true hoaxes), it's that they will not accomplish (in his view) what they set out to do because they are founded on unsound bases.
Rust is deliberately a weaker language for expressing library semantics. You can write libraries in C++ that cannot be written in Rust, that encapsulate semantics that cannot be captured in Rust. C++ library writers do, routinely. The C++ Standard Library has many components that could not be coded in Rust, that make the language more powerful for all users.
This makes Rust easier to learn, but it limits the libraries you can use, having learned it, and limits the libraries you can write.
This is a difficult tradeoff for any language design. Haskell is more powerful, too, and also harder to learn and to use well. (At the same time, its lack of destructors also limits it in ways that Rust and C++ do not suffer.)
The OOP -- inheritance, and virtual functions -- is a niche feature that is sometimes useful, but can often be emulated well enough with function pointers.
If it's implementation inheritance, then that was never a requirement for OO, seeing how prototype-based OO has been around for a very long time.
There are plenty of OOP flavours, just like there are plenty of FP flavours.
If one considers 100% Haskell's features as must have for a language to be considered FP, then OCaml and Standard ML are going to have a hard time to be considered FP.
Apple seems to think that anything that you put in dealloc should end up in the system (like unsubscribing from notifications).
C++ is a dangerous, powerhouse systems language. I think it really needs things like destructors, and I’m glad to see its continuing development.
Apple is amping up KVO, in general, which I like.
As an example of why this matters, I’ve got a class called TimeCapture in a project. If I want to instrument how long a block takes (full function, inside of an if, etc) I can add `TimeCapture tc(“my-metric-name”);` to the block and know that the destructor on that object will be called precisely at the end of that block (capturing the end time of the block)
I don’t know the rules for Swift or Ada or OP, but I’m guessing they’ll vary.
Not true. They run when the object is deallocated. In CPython if the object is not involved in or referenced from a cycle, that’s as soon as it goes out of scope: the ref count goes to 0 and the object gets deallocated.
This is trivial to check: create a structure with a noisy __del__ and create an instance from a function, call the function, del will run. The GC has no reason to run at this point, there’s no allocation requiring any sort of reclamation, but if you don’t trust that you can just `gc.disable()` and observe… the exact same behaviour.
That's a CPython implementation detail, not a guarantee that you can rely on.
For example, both PyPy[0] and Jython use tracing GCs where this is not true.
[0]: https://doc.pypy.org/en/latest/cpython_differences.html
Which would be why I specifically wrote « in CPython ».
And it still makes the original assertion completely incorrect. Python destructors do not run « down the road, during the next GC cycle ». They may, in certain cases or implementations.
> implementation detail
There is no guarantee that even CPython will keep the current behaviour. Ultimately, the promise you're given is that __del__ might be invoked by the system some point between "the object has no live references" and "never".
The original assertion gives a much closer intuition than your description of the current behaviour.
The original commenter made a specific assertion. I demonstrated that their assertion is not true.
It seems to me that there must be some other language that would have the c++ guarantee, but I don't know of it. (it isn't hard to implement, and c++ is well known enough that other languages designers can consider the pros and cons and surely someone else has decided it is worth it)
Rust's Drop[0] has basically the same guarantees as C++: the destructor will run right before the memory is freed (although it is possible in both cases to also leak both). Combine with Pin[1] if you need the exact memory location to be stable as well.
> it isn't hard to implement
Sadly, it's basically incompatible with tracing garbage collectors, since they make it completely unpredictable when the destructor will run.
So if you ever want to allow yourself to switch to tracing GC then you'll either have to disallow it completely, or bury it in a hidden corner of the docs with a load of caveats (like Python or Java). And in the latter case you'll still have people like the GP stumble upon it, say "oh, this looks neat", and set up a really painful trap for their future selves.
[0]: https://doc.rust-lang.org/stable/std/ops/trait.Drop.html
[1]: https://doc.rust-lang.org/stable/std/pin/index.html#drop-gua...
- the standard library design -- every object is refcounted and any code that references the object can add it to an autorelease pool, so you can't safely predict when dealloc will be invoked
- Objective C doesn't support stack-based objects
@autoreleasepool {
RaiObj* obj = [RaiObj new];
[obj autorelease];
//... stuff
}
"Finalize" on objects of type "Ada.Finalization.Controlled".
I mean, yes, those words are in there, but I'm responding to your words:
> Ada does not have destructors or anything analogous.
Which are factually wrong. Finalize is called automatically (per the link). And they are exactly what you say Ada lacks, analogues of destructors.
Your complaint, now, is that Finalize and Initialize don't automatically call the same functions in the parent. That's a separate issue, and doesn't demonstrate that Ada doesn't have this thing (a variant of destructors) which it very clearly has.
Or in the "PHP has no destructors"? - in that: PHP's object model is an "interesting" mixture of Java and C++. In regards to C++ it has detemrinsitric destructors, which enable RAII. The only complication is that all objects are reference counted (like shared_ptr in C++) and one can easily lose ownership from where one expects it to be. However if you keep an eye on ownership you can rely on reference count being decreased on function exit (be it regular exit or exception) and the destructor being called, in LIFO order as one expects. This isn't used much in PHP as you don't have to manage resources as often as with other languages/domains (in short lived request world one doesn't care whether a database connection is destroyed on function end or only on request shutdown, memory is handled automatically, etc.)
The same issue occurs in c++ if you're sloppy with shared_ptr. If you know what you're doing, you can break cycles with weak references in either language. Where Python has diapers, c++ has footguns aplenty.
But if you provide a non-deterministic mechanism on top of refcounting to break the cycles, and destructors aren't consistently deterministic already, why even bother with refcounting at all?
It is possible to contrive a graph data structure with cycles, but it is a bad (i.e. slow) representation not useful in production.