Участник:VitaliyFilippov/Закладки

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2011

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  • 30 Ноябрь, 19:39:49: Open-Source ~ Why The GIMP's User Interface Is Not As Terrible As You May Think
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  • 14 Ноябрь, 18:19:54: The Bulbdial Clock Kit — Evil Mad Scientist Laboratories
  • 14 Ноябрь, 02:47:58: Список алгоритмов и структур данных на C++ — Algorithms in Java
  • 11 Ноябрь, 11:19:06: #270852 — iptables: (patch) to add userspace support for kernel patch per-program per-connection filtering — Debian Bug report logs
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  • 09 Ноябрь, 12:38:57: Группа компаний «РусХим»
  • 09 Ноябрь, 03:33:43: c++ — Java operator overload — Stack Overflow

    There are a lot of posts complaining about operator overloading.

    I felt I had to clarify the «operator overloading» concepts, offering an alternative viewpoint on this concept.

    Code obfuscating?

    This argument is a fallacy.

    Obfuscating is possible in all languages…

    It is as easy to obfuscate code in C or Java through functions/methods than it is in C++ through operator overloads:

    // C++
    T     operator + (const T & a, const T & b) // add ?
    {
       T c     ;
       c    .value = a.value - b.value ; // substract !!!
           return c ;
    }

    // Java
    static T add (T a, T b) // add ?
    {
       T c     = new T() ;
       c    .value = a.value - b.value ; // substract !!!
           return c ;
    }

    /* C */
    T add     (T a, T b) /* add ? */
    {
       T c     ;
       c    .value = a.value - b.value ; /* substract !!! */
           return c ;
    }

    …Even in Java’s standard interfaces

    For another example, let’s see the Cloneable interface in Java: http://download.oracle.com/javase/7/docs/api/java/lang/Cloneable.html

    You are supposed to clone the object implementing this interface. But you could lie. And create a different object. In fact, this interface is so weak you could return another type of object altogether, just for the fun of it:

    class MySincereHandShake implements Cloneable
    {
            public Object clone()
            {
               return new MyVengefulKickInYourHead() ;
            }
    }

    As the Cloneable interface can be abused/obfuscated, should it be banned on the same grounds C++ operator overloading are supposed to be?

    We could overload the toString() method of a MyComplexNumber class to have it return the stringified hour of the day. Should the toString() overloading be banned, too? We could sabotage MyComplexNumber.equals to have it return a random value, modify the operands… etc. etc. etc..

    In Java, as in C++, or whatever language, the programmer must respect a minimum of semantics when writing code. This means implementing a add function that adds, and Cloneable implementation method that clones, and a ++ operator than increments.

    What’s obfuscating anyway?

    Now that we know that code can be sabotaged even through the pristine Java methods, we can ask ourselves about the real use of operator overloading in C++?

    Clear and natural notation: methods vs. operator overloading?

    We’ll compare below, for different cases, the «same» code in Java and C++, to have an idea of which kind of coding style is clearer.

    Natural comparisons:

    // C++ comparison for built-ins and user-defined types
    bool    isEqual          = A == B ;
    bool    isNotEqual       = A != B ;
    bool    isLesser         = A <  B ;
    bool    isLesserOrEqual  = A <= B ;

    // Java comparison for user-defined types
    boolean isEqual          = A.equals(B) ;
    boolean isNotEqual       = ! A.equals(B) ;
    boolean isLesser         = A.comparesTo(B) < 0 ;
    boolean isLesserOrEqual  = A.comparesTo(B) <= 0 ;

    Please note that A and B could be of any type in C++, as long as the operator overloads are provided. In Java, when A and B are not primitives, the code can become very confusing, even for primitive-like objects (BigInteger, etc.)…

    Natural array/container accessors and subscripting:

    // C++ container accessors, more natural
    value            = myArray[25] ;         // subscript operator
    value            = myVector[25] ;        // subscript operator
    value            = myString[25] ;        // subscript operator
    value            = myMap[«25»] ;         // subscript operator
    myArray    [25]  = value ;               // subscript operator
    myVector    [25] = value ;               // subscript operator
    myString    [25] = value ;               // subscript operator
    myMap    [«25»]  = value ;               // subscript operator

    // Java container accessors, each one has its special notation
    value            = myArray[25] ;         // subscript operator
    value            = myVector.get(25) ;    // method get
    value            = myString.charAt(25) ; // method charAt
    value            = myMap.get(«25») ;     // method get
    myArray    [25]  = value ;               // subscript operator
    myVector    .set(25, value) ;            // method set
    myMap    .set(«25», value) ;             // method set

    In Java, we see that for each container to do the same thing (access its content through an index or identifier), we have a different way to do it, which is confusing.

    In C++, each container uses the same way to access its content, thanks to operator overload.

    Natural advanced types manipulation

    The examples below use a Matrix object, found using the first links found on Google for «Java Matrix object" and «c++ Matrix object":

    // C++ YMatrix matrix implementation on CodeProject
    // http://www.codeproject.com/KB/architecture/ymatrix.aspx
    // A, B, C, D, E, F are Matrix objects;
    E     =  A * (B / 2) ;
    E     += (A - B) * (C + D) ;
    F     =  E ;                  // deep copy of the matrix

    // Java JAMA matrix implementation (seriously…)
    // http://math.nist.gov/javanumerics/jama/doc/
    // A, B, C, D, E, F are Matrix objects;
    E     = A.times(B.times(2)) ;
    E    .plusEquals(A.minus(B).times(C.plus(D))) ;
    F     = E.copy() ;            // deep copy of the matrix

    And this is not limited to matrices. The BigInteger and BigDecimal classes of Java suffer from the same confusing verbosity, whereas their equivalent in C++ are as clear as built-in types.

    Natural iterators:

    // C++ Random Access iterators
    ++it ;                  // move to the next item
    --it ;                  // move to the previous item
    it     += 5 ;               // move to the next 5th item (random access)
    value     = *it ;           // gets the value of the current item
    *it = 3.1415 ;          // sets the value 3.1415 to the current item
    (*it).foo() ;           // call method foo() of the current item

    // Java ListIterator<E> «bi-directional» iterators
    value     = it.next() ;     // move to the next item & return the value
    value     = it.previous() ; // move to the previous item & return the value
    it    .set(3.1415) ;        // sets the value 3.1415 to the current item

    Natural functors:

    // C++ Functors
    myFunctorObject    («Hello World», 42) ;

    // Java Functors ???
    myFunctorObject    .execute(«Hello World», 42) ;

    Text concatenation:

    // C++ stream handling (with the << operator)
                        stringStream       << "Hello " << 25 << « World» ;
                        fileStream         << "Hello " << 25 << « World» ;
                        outputStream       << "Hello " << 25 << « World» ;
                        networkStream      << "Hello " << 25 << « World» ;
    anythingThatOverloadsShiftOperator     << "Hello " << 25 << « World» ;

    // Java concatenation
    myStringBuffer    .append("Hello ").append(25).append(« World») ;

    Ok, in Java you can use MyString = "Hello " + 25 + « World» ; too… But, wait a second: This is operator overloading, isn’t it? Isn’t it cheating???

    :-D

    Generic code?

    The same generic code modifying operands should be usable both for built-ins/primitives (which have no interfaces in Java), standard objects (which could not have the right interface), and user-defined objects.

    For example, calculating the average value of two values of arbitrary types:

    // C++ primitive/advanced types
    template<typename T>
    T getAverage    (const T & p_lhs, const T & p_rhs)
    {
           return (p_lhs + p_rhs) / 2 ;
    }

    int     intValue     = getAverage(25, 42) ;
    double  doubleValue  = getAverage(25.25, 42.42) ;
    complex complexValue     = getAverage(cA, cB) ; // cA, cB are complex
    Matrix  matrixValue  = getAverage(mA, mB) ; // mA, mB are Matrix

    // Java primitive/advanced types
    // It won’t really work in Java, even with generics. Sorry.

    Discussing operator overloading

    How that we saw fair comparisons between C++ code using operator overloading, and the same code in Java, we can know discuss the «operator overloading» as a concept.

    Operator overloading existed since before computers

    Even outside of computer science, there are operator overloading: For example, in mathematics, operators like +, -, *, etc. are overloaded.

    Indeed, the signification of +, -, *, etc. changes depending on the types of the operands (numerics, vectors, quantum wave functions, matrices, etc.).

    Most of us, as part of our science courses, learned multiple significations for operators, depending on the types of the operands. Did we find them confusing, them?

    Operator overloading depends on its operands

    This is the most important part of operator overloading: Like in mathematics, or in physics, the operation depends on its operands' types.

    So, know the type of the operand, and you will know the effect of the operation.

    Even C and Java have (hardcoded) operator overloading

    In C, the real behavior of an operator will change according to its operands. For example, adding two integers is different than adding two doubles, or even one integer and one double. There is even the whole pointer arithmetic domain (without casting, you can add to a pointer an integer, but you cannot add two pointers…).

    In Java, there is no pointer arithmetics, but someone still found string concatenation without the + operator would be ridiculous enough to justify an exception in the «operator overloading is evil» creed.

    It’s just that you, as a C (for historical reasons) or Java (for personal reasons, see below) coder, you can’t provide your own.

    In C++, operator overloading is not optional…

    In C++, operator overloading for built-in types is not possible (and this is a good thing), but user-defined types can have user-defined operator overloads.

    As already said earlier, in C++, and to the contrary to Java, user-types are not considered second-class citizens of the language, when compared to built-in types. So, if built-in types have operators, user types should be able to have them, too.

    The truth is that, like the toString(), clone(), equals() methods are for Java (i.e. quasi-standard-like), C++ operator overloading is so much part of C++ that it becomes as natural as the original C operators, or the before mentioned Java methods.

    Combined with template programming, operator overloading becomes a well known design pattern. In fact, you cannot go very far in STL without using overloaded operators, and overloading operators for your own class.

    …but it should not be abused

    Operator overloading should strive to respect the semantics of the operator. Do not substract in a + operator (as in «do not substract in a add function», or «return crap in a clone method»).

    Cast overloading can be very dangerous because they can lead to ambiguities. So they should really be reserved for well defined cases. As for && and ||, do not ever overload them unless you really know what you’re doing, as you’ll loose the the short circuit evaluation that the native operators && and || enjoy.

    So… Ok… Then why it is not possible in Java?

    Because James Gosling said so:

    I left out operator overloading as a fairly personal choice because I had seen too many people abuse it in C++.

    James Gosling. Source: http://www.gotw.ca/publications/c_family_interview.htm

    Please compare Gosling’s text above with Stroustrup’s below:

    Many C++ design decisions have their roots in my dislike for forcing people to do things in some particular way […] Often, I was tempted to outlaw a feature I personally disliked, I refrained from doing so because I did not think I had the right to force my views on others.

    Bjarne Stroustrup. Source: The Desing and Evolution of C++ (1.3 General Background)

    Would operator overloading benefit Java?

    Some objects would greatly benefit from operator overloading (concrete or numerical types, like BigDecimal, complex numbers, matrices, containers, iterators, comparators, parsers etc.).

    In C++, you can profit from this benefit because of Stroustrup’s humility. In Java, you’re simply screwed because of Gosling’s personal choice.

    Could it be added to Java?

    The reasons for not adding operator overloading now in Java could be a mix of internal politics, allergy to the feature, distrust of developers (you know, the saboteur ones that seem to haunt Java teams…), compatibility with the previous JVMs, time to write a correct specification, etc..

    So don’t hold your breath waiting for this feature…

    But they do it in C#!!!

    Yeah…

    While this is far from being the only difference between the two languages, this one never fails to amuse me.

    Apparently, the C# folks, with their «every primitive is a struct, and a struct derives from Object», got it right at first try.

  • 07 Ноябрь, 14:40:11: Sweet Home 3D
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  • 01 Ноябрь, 21:41:00: How to hack Acoms AS-16 servos — Blog — Jamie Matthews

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  • 12 Июль, 00:08:33: Киряем! — Выпуск #179
    География дома

    Сегодня я расскажу Вам, как выучить географию, не выходя из квартиры. Гардероб. Гардероб это Китай. Да, Вы можете говорить кому угодно HUGO BOSS, COVALLI, GUCCI (показывает фигу) КИ-ТАЙ.
    Антресоли. Антресоли это Монголия, потому что нихрена не понятно, что там лежит, что там происходит, вообще нихрена не понятно.
    Кухня, кухня это Ближний Восток, потому что там постоянно, что-то готовится все на ножах, постоянный фарш, мясо по стенам, слезы, сопли и в центре этого диктатор, который воняет химическим оружием.
    Если Вы живете с тещей, то комната тещи это США. Открываем дверь — вот оно, тупое лицо руководителя государства. А если Вы только сунетесь на Ближний Восток, ЖОПА, война обеспечена.
    Туалет, туалет это Голландия. Потому что неровно положенный кафель постоянно напоминает Вам, что его клали какие-то пидарасы.
    Телевизор, телевизор это Украина. Потому что пульт управления гуляет по рукам, поэтому каждую минуту на Украине новая программа.
    Кот, если у Вас живет кот, то это Прибалтика. Ест на халяву, пьет на халяву, мелко пакостит и делает вид, что нихрена не понимает по-русски.
    Холодильник — это Евросоюз. Чего там только нет, и вроде бы все лежит аккуратно, по полочкам, но обязательно что-то одно воняет. Как только жрать нечего, сразу все лезут в Евросоюз, и Прибалтика тоже сует туда свой нос.
    Балкон — это Египет. Нигде в мире Вы не найдете большего количества древностей, причем этого говна там целые пирамиды.
    Старый молоток. Старый молоток — это Люксембург. А где он? Да х*й его знает, где он!
    Гараж — это Париж. В центре стоит большая груда железа, под которой можно тр*хаться часами.
    И собственно Вы во всем этом Россия. До поры до времени улыбаетесь США. Кормите Прибалтику. Боретесь за право обладания пультом управления Украины. Соприкасаетесь с Евросоюзом. Но сдохнуть хотите в Париже…
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