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  • naming a function that exhibits "set if not equal" behavior

    - by Chris Sears
    This might be an odd question, but I'm looking for a word to use in a function name. I'm normally good at coming up with succinct, meaningful function names, but this one has me stumped so I thought I'd appeal for help. The function will take some desired state as an argument and compare it to the current state. If no change is needed, the function will exit normally without doing anything. Otherwise, the function will take some action to achieve the desired state. For example, if wanted to make sure the front door was closed, i might say: my_house.<something>_front_door('closed') What word or term should use in place of the something? I'd like it to be short, readable, and minimize the astonishment factor. A couple clarifying points... I would want someone calling the function to intuitively know they didn't need to wrap the function an 'if' that checks the current state. For example, this would be bad: if my_house.front_door_is_open(): my_house.<something>_front_door('closed') Also, they should know that the function won't throw an exception if the desired state matches the current state. So this should never happen: try: my_house.<something>_front_door('closed') except DoorWasAlreadyClosedException: pass Here are some options I've considered: my_house.set_front_door('closed') my_house.setne_front_door('closed') # ne=not equal, from the setne x86 instruction my_house.ensure_front_door('closed') my_house.configure_front_door('closed') my_house.update_front_door('closed') my_house.make_front_door('closed') my_house.remediate_front_door('closed') And I'm open to other forms, but most I've thought of don't improve readability. Such as... my_house.ensure_front_door_is('closed') my_house.conditionally_update_front_door('closed') my_house.change_front_door_if_needed('closed') Thanks for any input!

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  • Trying to reduce the speed overhead of an almost-but-not-quite-int number class

    - by Fumiyo Eda
    I have implemented a C++ class which behaves very similarly to the standard int type. The difference is that it has an additional concept of "epsilon" which represents some tiny value that is much less than 1, but greater than 0. One way to think of it is as a very wide fixed point number with 32 MSBs (the integer parts), 32 LSBs (the epsilon parts) and a huge sea of zeros in between. The following class works, but introduces a ~2x speed penalty in the overall program. (The program includes code that has nothing to do with this class, so the actual speed penalty of this class is probably much greater than 2x.) I can't paste the code that is using this class, but I can say the following: +, -, +=, <, > and >= are the only heavily used operators. Use of setEpsilon() and getInt() is extremely rare. * is also rare, and does not even need to consider the epsilon values at all. Here is the class: #include <limits> struct int32Uepsilon { typedef int32Uepsilon Self; int32Uepsilon () { _value = 0; _eps = 0; } int32Uepsilon (const int &i) { _value = i; _eps = 0; } void setEpsilon() { _eps = 1; } Self operator+(const Self &rhs) const { Self result = *this; result._value += rhs._value; result._eps += rhs._eps; return result; } Self operator-(const Self &rhs) const { Self result = *this; result._value -= rhs._value; result._eps -= rhs._eps; return result; } Self operator-( ) const { Self result = *this; result._value = -result._value; result._eps = -result._eps; return result; } Self operator*(const Self &rhs) const { return this->getInt() * rhs.getInt(); } // XXX: discards epsilon bool operator<(const Self &rhs) const { return (_value < rhs._value) || (_value == rhs._value && _eps < rhs._eps); } bool operator>(const Self &rhs) const { return (_value > rhs._value) || (_value == rhs._value && _eps > rhs._eps); } bool operator>=(const Self &rhs) const { return (_value >= rhs._value) || (_value == rhs._value && _eps >= rhs._eps); } Self &operator+=(const Self &rhs) { this->_value += rhs._value; this->_eps += rhs._eps; return *this; } Self &operator-=(const Self &rhs) { this->_value -= rhs._value; this->_eps -= rhs._eps; return *this; } int getInt() const { return(_value); } private: int _value; int _eps; }; namespace std { template<> struct numeric_limits<int32Uepsilon> { static const bool is_signed = true; static int max() { return 2147483647; } } }; The code above works, but it is quite slow. Does anyone have any ideas on how to improve performance? There are a few hints/details I can give that might be helpful: 32 bits are definitely insufficient to hold both _value and _eps. In practice, up to 24 ~ 28 bits of _value are used and up to 20 bits of _eps are used. I could not measure a significant performance difference between using int32_t and int64_t, so memory overhead itself is probably not the problem here. Saturating addition/subtraction on _eps would be cool, but isn't really necessary. Note that the signs of _value and _eps are not necessarily the same! This broke my first attempt at speeding this class up. Inline assembly is no problem, so long as it works with GCC on a Core i7 system running Linux!

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  • Perl ||= operator for PHP and Javascript

    - by zaf
    Just been re-introduced to the Perl '||=' operator from the classic Orcish Maneuver example: keys my %or_cache = @in; @out = sort { ($or_cache{$a} ||= KEY($a)) cmp ($or_cache{$b} ||= KEY($b)) } @in; Is this operator available in PHP and Javascript? And if not, do these two languages allow user defined operators?

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  • undefined C/C++ symbol as operator

    - by uray
    I notice that the character/symbol '`' and '@' is not used as an operator in C/C++, does anyone know the reason or historically why its so? if its really not used, is it safe to define those symbols as another operator/statement using #define?

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  • Javascript IN operator compatibility

    - by jAndy
    Hi Folks, Can someone tell me since which ECMA version the IN operator is available and which browsers (versions) support it ? Explanation: The IN-operator can be used like the following: var myObject = { Firstname: 'Foo', Lastname: 'Bar' }; if('Lastname' in myObject){ // Lastname is an attribute of myObject }

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  • c++ global operator not playing well with template class

    - by John
    ok, i found some similar posts on stackoverflow, but I couldn't find any that pertained to my exact situation and I was confused with some of the answers given. Ok, so here is my problem: I have a template matrix class as follows: template <typename T, size_t ROWS, size_t COLS> class Matrix { public: template<typename, size_t, size_t> friend class Matrix; Matrix( T init = T() ) : _matrix(ROWS, vector<T>(COLS, init)) { /*for( int i = 0; i < ROWS; i++ ) { _matrix[i] = new vector<T>( COLS, init ); }*/ } Matrix<T, ROWS, COLS> & operator+=( const T & value ) { for( vector<T>::size_type i = 0; i < this->_matrix.size(); i++ ) { for( vector<T>::size_type j = 0; j < this->_matrix[i].size(); j++ ) { this->_matrix[i][j] += value; } } return *this; } private: vector< vector<T> > _matrix; }; and I have the following global function template: template<typename T, size_t ROWS, size_t COLS> Matrix<T, ROWS, COLS> operator+( const Matrix<T, ROWS, COLS> & lhs, const Matrix<T, ROWS, COLS> & rhs ) { Matrix<T, ROWS, COLS> returnValue = lhs; return returnValue += lhs; } To me, this seems to be right. However, when I try to compile the code, I get the following error (thrown from the operator+ function): binary '+=' : no operator found which takes a right-hand operand of type 'const matrix::Matrix<T,ROWS,COLS>' (or there is no acceptable conversion) I can't figure out what to make of this. Any help if greatly appreciated!

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  • Why isn't the boost::shared_ptr -> operator inlined?

    - by Alan
    Since boost::shared_ptr could be called very frequently and simply returns a pointer, isn't the -> operator a good candidate for being inlined? T * operator-> () const // never throws { BOOST_ASSERT(px != 0); return px; } Would a good compiler automatically inline this anyway? Should I lose any sleep over this? :-)

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  • What does the C# operator => mean?

    - by Mr. Mark
    Answers to a recent post (Any chances to imitate times() Ruby method in C#?) use the = operator in the usage examples. What does this operator do? I can't locate it in my C# book, and it is hard to search for symbols like this online. (I couldn't find it.)

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  • PHP: Object Oriented Programming -> Operator

    - by oman9589
    So I've been reading through the book PHP Solutions, Dynamic Web Design Made Easy by David Powers. I read through the short section on Object Oriented PHP, and I am having a hard time grasping the idea of the - operator. Can anyone try to give me a solid explanation on the - operator in OOP PHP? Example: $westcost = new DateTimeZone('America/Los_Angeles'); $now->setTimezone($westcoast); Also,a more general example: $someObject->propertyName Thanks

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  • Is return an operator or a function?

    - by eSKay
    This is too basic I think, but how do both of these work? return true; // 1 and return (true); // 2 Similar: sizeof, exit My guess: If return was a function, 1 would be erroneous. So, return should be a unary operator that can also take in brackets... pretty much like unary minus: -5 and -(5), both are okay. Is that what it is - a unary operator?

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  • binary operator "<"

    - by md004
    Consider this expression as a "selection" control structure on integer "x": 0 < x < 10, with the intention that the structure returns TRUE if "x" is in the range 1..9. Explain why a compiler should not accept this expression. (In particular, what are the issues regarding the binary operator "<"? Explain how a prefix operator could be introduced so the expression can be successfully processed.

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  • SQL SERVER – Fix: Error : 402 The data types ntext and varchar are incompatible in the equal to operator

    - by pinaldave
    Some errors are very simple to understand but the solution of the same is not easy to figure out. Here is one of the similar errors where it clearly suggests where the problem is but does not tell what is the solution. Additionally, there are multiple solutions so developers often get confused with which one is correct and which one is not correct. Let us first recreate scenario and understand where the problem is. Let us run following USE Tempdb GO CREATE TABLE TestTable (ID INT, MyText NTEXT) GO SELECT ID, MyText FROM TestTable WHERE MyText = 'AnyText' GO DROP TABLE TestTable GO When you run above script it will give you following error. Msg 402, Level 16, State 1, Line 1 The data types ntext and varchar are incompatible in the equal to operator. One of the questions I often receive is that voucher is for sure compatible to equal to operator, then why does this error show up. Well, the answer is much simpler I think we have not understood the error message properly. Please see the image below. The next and varchar are not compatible when compared with each other using equal sign. Now let us change the data type on the right side of the string to nvarchar from varchar. To do that we will put N’ before the string. USE Tempdb GO CREATE TABLE TestTable (ID INT, MyText NTEXT) GO SELECT ID, MyText FROM TestTable WHERE MyText = N'AnyText' GO DROP TABLE TestTable GO When you run above script it will give following error. Msg 402, Level 16, State 1, Line 1 The data types ntext and nvarchar are incompatible in the equal to operator. You can see that error message also suggests that now we are comparing next to nvarchar. Now as we have understood the error properly, let us see various solutions to the above problem. Solution 1: Convert the data types to match with each other using CONVERT function. Change the datatype of the MyText to nvarchar. SELECT ID, MyText FROM TestTable WHERE CONVERT(NVARCHAR(MAX), MyText) = N'AnyText' GO Solution 2: Convert the data type of columns from NTEXT to NVARCHAR(MAX) (TEXT to VARCHAR(MAX) ALTER TABLE TestTable ALTER COLUMN MyText NVARCHAR(MAX) GO Now you can run the original query again and it will work fine. Solution 3: Using LIKE command instead of Equal to command. SELECT ID, MyText FROM TestTable WHERE MyText LIKE 'AnyText' GO Well, any of the three of the solutions will work. Here is my suggestion if you can change the column data type from ntext or text to nvarchar or varchar, you should follow that path as text and ntext datatypes are marked as deprecated. All developers any way to change the deprecated data types in future, it will be a good idea to change them right early. If due to any reason you can not convert the original column use Solution 1 for temporary fix. Solution 3 is the not the best solution and use it as a last option. Did I miss any other method? If yes, please let me know and I will add the solution to original blog post with due credit. Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: PostADay, SQL, SQL Authority, SQL Error Messages, SQL Query, SQL Server, SQL Tips and Tricks, T SQL, Technology

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  • friendship and operator overloading help

    - by sil3nt
    hello there, I have the following class #ifndef Container_H #define Container_H #include <iostream> using namespace std; class Container{ friend bool operator==(const Container &rhs,const Container &lhs); public: void display(ostream & out) const; private: int sizeC; // size of Container int capacityC; // capacity of dynamic array int * elements; // pntr to dynamic array }; ostream & operator<< (ostream & out, const Container & aCont); #endif and this source file #include "container.h" /*----------------------------********************************************* note: to test whether capacityC and sizeC are equal, must i add 1 to sizeC? seeing as sizeC starts off with 0?? */ Container::Container(int maxCapacity){ capacityC = maxCapacity; elements = new int [capacityC]; sizeC = 0; } Container::~Container(){ delete [] elements; } Container::Container(const Container & origCont){ //copy constructor? int i = 0; for (i = 0; i<capacityC; i++){ //capacity to be used here? (*this).elements[i] = origCont.elements[i]; } } bool Container::empty() const{ if (sizeC == 0){ return true; }else{ return false; } } void Container::insert(int item, int index){ if ( sizeC == capacityC ){ cout << "\n*** Next: Bye!\n"; return; // ? have return here? } if ( (index >= 0) && (index <= capacityC) ){ elements[index] = item; sizeC++; } if ( (index < 0) && (index > capacityC) ){ cout<<"*** Illegal location to insert--"<< index << ". Container unchanged. ***\n"; }//error here not valid? according to original a3? have i implemented wrong? } void Container::erase(int index){ if ( (index >= 0) && (index <= capacityC) ){ //correct here? legal location? int i = 0; while (i<capacityC){ //correct? elements[index] = elements[index+1]; //check if index increases here. i++; } sizeC=sizeC-1; //correct? updated sizeC? }else{ cout<<"*** Illegal location to be removed--"<< index << ". Container unchanged. ***\n"; } } int Container::size()const{ return sizeC; //correct? } /* bool Container::operator==(const Container &rhs,const Container &lhs){ int equal = 0, i = 0; for (i = 0; i < capacityC ; i++){ if ( rhs.elements[i] == lhs.elements[i] ){ equal++; } } if (equal == sizeC){ return true; }else{ return false; } } ostream & operator<< (ostream & out, const Container & aCont){ int i = 0; for (i = 0; i<sizeC; i++){ out<< aCont.elements[i] << " " << endl; } } */ I dont have the other functions in the header file (just a quikie). Anyways, the last two functions in "/* */" I cant get to work, what am I doing wrong here? the first function is to see whether the two arrays are equal to one another

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  • Polynomial operations using operator overloading

    - by Vlad
    I'm trying to use operator overloading to define the basic operations (+,-,*,/) for my polynomial class but when i run the program it crashes and my computer frozes. Update3 Ok i successfully done the first two operations(+,-). Now at multiplication, after multiplying each term of the first polynomial with each of the second i want to sort the poly list descending and then if there are more than one term with the same power to merge them in only one term, but for some reason it doesn't compile because of the sort function which doesn't work. Here's what I got: polinom operator*(const polinom& P) const { polinom Result; constIter i, j, lastItem = Result.poly.end(); Iter it1, it2; int nr_matches; for (i = poly.begin() ; i != poly.end(); i++) { for (j = P.poly.begin(); j != P.poly.end(); j++) Result.insert(i->coef * j->coef, i->pow + j->pow); } sort(Result.poly.begin(), Result.poly.end(), SortDescending()); lastItem--; while (true) { nr_matches = 0; for (it1 = Result.poly.begin(); it < lastItem; it1++) { for (it2 = it1 + 1;; it2 <= lastItem; it2++){ if (it2->pow == it1->pow) { it1->coef += it2->coef; nr_matches++; } } Result.poly.erase(it1 + 1, it1 + (nr_matches + 1)); } return Result; } Also here's SortDescending: struct SortDescending { bool operator()(const term& t1, const term& t2) { return t2.pow < t1.pow; } }; What did i do wrong? Thanks!

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  • Template operator linker error

    - by Dani
    I have a linker error I've reduced to a simple example. The build output is: debug/main.o: In function main': C:\Users\Dani\Documents\Projects\Test1/main.cpp:5: undefined reference tolog& log::operator<< (char const (&) [6])' collect2: ld returned 1 exit status It looks like the linker ignores the definition in log.cpp. I also cant put the definition in log.h because I include the file alot of times and it complains about redefinitions. main.cpp: #include "log.h" int main() { log() << "hello"; return 0; } log.h: #ifndef LOG_H #define LOG_H class log { public: log(); template<typename T> log &operator <<(T &t); }; #endif // LOG_H log.cpp: #include "log.h" #include <iostream> log::log() { } template<typename T> log &log::operator <<(T &t) { std::cout << t << std::endl; return *this; }

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  • How to make std::vector's operator[] compile doing bounds checking in DEBUG but not in RELEASE

    - by Edison Gustavo Muenz
    I'm using Visual Studio 2008. I'm aware that std::vector has bounds checking with the at() function and has undefined behaviour if you try to access something using the operator [] incorrectly (out of range). I'm curious if it's possible to compile my program with the bounds checking. This way the operator[] would use the at() function and throw a std::out_of_range whenever something is out of bounds. The release mode would be compiled without bounds checking for operator[], so the performance doesn't degrade. I came into thinking about this because I'm migrating an app that was written using Borland C++ to Visual Studio and in a small part of the code I have this (with i=0, j=1): v[i][j]; //v is a std::vector<std::vector<int> > The size of the vector 'v' is [0][1] (so element 0 of the vector has only one element). This is undefined behaviour, I know, but Borland is returning 0 here, VS is crashing. I like the crash better than returning 0, so if I can get more 'crashes' by the std::out_of_range exception being thrown, the migration would be completed faster (so it would expose more bugs that Borland was hiding).

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  • c# "==" operator : compiler behaviour with different structs

    - by Moe Sisko
    Code to illustrate : public struct MyStruct { public int SomeNumber; } public string DoSomethingWithMyStruct(MyStruct s) { if (s == null) return "this can't happen"; else return "ok"; } private string DoSomethingWithDateTime(DateTime s) { if (s == null) return "this can't happen"; // XX else return "ok"; } Now, "DoSomethingWithStruct" fails to compile with : "Operator '==' cannot be applied to operands of type 'MyStruct' and '<null>'". This makes sense, since it doesn't make sense to try a reference comparison with a struct, which is a value type. OTOH, "DoSomethingWithDateTime" compiles, but with compiler warning : "Unreachable code detected" at line marked "XX". Now, I'm assuming that there is no compiler error here, because the DateTime struct overloads the "==" operator. But how does the compiler know that the code is unreachable ? e.g. Does it look inside the code which overloads the "==" operator ? (This is using Visual Studio 2005 in case that makes a difference). Note : I'm more curious than anything about the above. I don't usually try to use "==" on structs and nulls.

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  • Java Newbie can't do simple Math, operator error

    - by elguapo-85
    Trying to do some really basic math here, but my lack of understanding of Java is causing some problems for me. double[][] handProbability = new double[][] {{0,0,0},{0,0,0},{0,0,0}}; double[] handProbabilityTotal = new double[] {0,0,0}; double positivePot = 0; double negativePot = 0; int localAhead = 0; int localTied = 1; int localBehind = 2; //do some stuff that adds values to handProbability and handProbabilityTotal positivePot = (handProbability[localBehind][localAhead] + (handProbability[localBehind][localTied] / 2.0) + (handProbability[localTied][localAhead] / 2.0) ) / (handProbabilityTotal[localBehind] + (handProbability[localTied] / 2.0)); negativePot = (handProbability[localAhead][localBehind] + (handProbability[localAhead][localTied] / 2.0) + (handProbability[localTied][localBehind] / 2.0) ) / (handProbabilityTotal[localAhead] + (handProbabilityTotal[localTied] / 2.0)); The last two lines are giving me problems (sorry for their lengthiness). Compiler Errors: src/MyPokerClient/MyPokerClient.java:180: operator / cannot be applied to double[],double positivePot = ( handProbability[localBehind][localAhead] + (handProbability[localBehind][localTied] / 2.0) + (handProbability[localTied][localAhead] / 2.0) ) / (handProbabilityTotal[localBehind] + (handProbability[localTied] / 2.0) ); ^ src/MyPokerClient/MyPokerClient.java:180: operator + cannot be applied to double, positivePot = ( handProbability[localBehind][localAhead] + (handProbability[localBehind][localTied] / 2.0) + (handProbability[localTied][localAhead] / 2.0) ) / (handProbabilityTotal[localBehind] + (handProbability[localTied] / 2.0) ); ^ src/MyPokerClient/MyPokerClient.java:180: operator / cannot be applied to double, positivePot = ( handProbability[localBehind][localAhead] + (handProbability[localBehind][localTied] / 2.0) + (handProbability[localTied][localAhead] / 2.0) ) / (handProbabilityTotal[localBehind] + (handProbability[localTied] / 2.0) ); Not really sure what the problem is. You shouldn't need anything special for basic math, right?

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  • Using overloaded operator== in a generic function

    - by Dimitri C.
    Consider the following code: class CustomClass { public CustomClass(string value) { m_value = value; } public static bool operator==(CustomClass a, CustomClass b) { return a.m_value == b.m_value; } public static bool operator!=(CustomClass a, CustomClass b) { return a.m_value != b.m_value; } public override bool Equals(object o) { return m_value == (o as CustomClass).m_value; } public override int GetHashCode() { return 0; /* not needed */ } string m_value; } class G { public static bool enericFunction1<T>(T a1, T a2) where T : class { return a1.Equals(a2); } public static bool enericFunction2<T>(T a1, T a2) where T : class { return a1==a2; } } Now when I call both generic functions, one succeeds and one fails: var a = new CustomClass("same value"); var b = new CustomClass("same value"); Debug.Assert(G.enericFunction1(a, b)); // Succeeds Debug.Assert(G.enericFunction2(a, b)); // Fails Apparently, G.enericFunction2 executes the default operator== implementation instead of my override. Can anybody explain why this happens?

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