Цитата(Bulat @ 6.12.2013, 07:19  ) | | К эрлангу точно никак. |
Это смотря http://www.infoq.com/interviews/johnson-armstrong-oop
| Скрытый текст |
3. Is Erlang object oriented?
Joe Armstrong: Smalltalk got a lot of the things right. So if your question is about what I think about object oriented programming, I sort of changed my mind over that. I wrote a an article, a blog thing, years ago - Why object oriented programming is silly. I mainly wanted to provoke people with it. They had a quite interesting response to that and I managed to annoy a lot of people, which was part of the intention actually. I started wondering about what object oriented programming was and I thought Erlang wasn't object oriented, it was a functional programming language.
Then, my thesis supervisor said "But you're wrong, Erlang is extremely object oriented". He said object oriented languages aren't object oriented. I might think, though I'm not quite sure if I believe this or not, but Erlang might be the only object oriented language because the 3 tenets of object oriented programming are that it's based on message passing, that you have isolation between objects and have polymorphism.
Alan Kay himself wrote this famous thing and said "The notion of object oriented programming is completely misunderstood. It's not about objects and classes, it's all about messages". He wrote that and he said that the initial reaction to object oriented programming was to overemphasize the classes and methods and under emphasize the messages and if we talk much more about messages then it would be a lot nicer. The original Smalltalk was always talking about objects and you sent messages to them and they responded by sending messages back.
But you don't really do that and you don't really have isolation which is one of the problems. Dan Ingalls said yesterday (I thought it was very nice) about messaging that once you got messaging, you don't have to care where the message came from. You don't really have to care, the runtime system has to organize the delivery of the message, we don't have to care about how it's processed. It sort of decouples the sender and the receiver in this kind of mutual way. That's why I love messaging.
The 3 things that object oriented programming has it's messaging, which is possibly the most important thing. The next thing is isolation and that's what I talked about earlier, that my program shouldn't crash your program, if the 2 things are isolated, then any mistakes I make in my program will not crash your program. This is certainly not true with Java. You cannot take 2 Java applications, bung them in the JVM and one of them still halts the machine and the other one will halt as well. You can crash somebody else's application, so they are not isolated.
The third thing you want is polymorphism. Polymorphism is especially regarding messaging, that's just there for the programmer's convenience. It's very nice to have for all objects or all processes or whatever you call them, to have a printMe method - "Go print yourself" and then they print themselves. That's because the programmers, if they all got different names, the programmer is never going to remember this, so it's a polymorphism. It just means "OK, all objects have a printMe method. All objects have a what's your size method or introspection method."
Erlang has got all these things. It's got isolation, it's got polymorphism and it's got pure messaging. From that point of view, we might say it's the only object oriented language and perhaps I was a bit premature in saying that object oriented languages are about. You can try it and see it for yourself.
Ralph Johnson: The thing about Erlang is that it's in some sense 2 languages, at least you program it 2 levels because one is the functional language that you use to write a single process and then there is what you think about all these processes and how do they interact, one process is sending messages to the other. At a higher level, that Erlang is object oriented, at the lowest level it's a pure functional language and that's how it got advertised for a long time.
At a higher level, when you are looking at it more from an architectural and high level design it is quite object oriented. I think you are redefining isolationism. It's all running on one computer and if one process goes wild, it hogs the processor. I think they look more like the importance of garbage collection so that you don't have to make sure that you agree on how you're releasing things. The only way in Smalltalk to interact with an object is send it a message, but the issue is what message do you have. It's the same thing in Erlang.
If you allow a huge number of messages that allow, return all the values of your local variables and that everybody's send you messages and you'll set the values of your local messages, if you did something like that, you'd basically lose a lot of the value of the isolationism. That's why you have to design things properly. The language offers some mechanism.
Joe Armstrong: It's useful when we've got million core computers.
|
| Цитата(Bulat @ 6.12.2013, 07:19 ) | | Там просто нет такого понятия - переменная. |
Это https://gist.github.com/mwotton/6862813. =)
| Скрытый текст |
| Код |
%% Server that echos all msgs to console.
-module(echo).
-export([start/0, print/1, stop/0]).
%% API
start() ->
register(?MODULE, spawn(fun loop1/0)),
ok.
stop() ->
?MODULE ! stop,
ok.
print(Msg) ->
?MODULE ! {print, Msg},
ok.
loop1() ->
loop(0).
%% Impl
loop(N) ->
receive
{print, Msg} ->
io:format("~w ~p~n", [N, Msg]),
loop(N+1);
stop ->
ok
end.
|
| Код |
10> c(echo).
{ok,echo}
11> echo:start()
11> .
ok
12> echo:print(hi).
0 hi
ok
13> echo:print(hi).
1 hi
ok
14> echo:print(hi).
2 hi
ok
15>
|
|
|
половая дискриминация!!!