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  • Perl Hash Slice, Replication x Operator, and sub params

    - by user210757
    Ok, I understand perl hash slices, and the "x" operator in Perl, but can someone explain the following code example from here (slightly simplified)? sub test{ my %hash; @hash{@_} = (undef) x @_; } Example Call to sub: test('one', 'two', 'three'); This line is what throws me: @hash{@_} = (undef) x @_; It is creating a hash where the keys are the parameters to the sub and initializing to undef, so: %hash: 'one' = undef, 'two' = undef, 'three' = undef The rvalue of the x operator should be a number; how is it that @_ is interpreted as the length of the sub's parameter array? I would expect you'd at least have to do this: @hash{@_} = (undef) x length(@_);

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  • Disallow using comma operator

    - by RiaD
    I never use the comma operator. But sometimes, when I write some recursions, I make a stupid mistake: I forget the function name. That's why the last operand is returned, not the result of a recursion call. Simplified example: int binpow(int a,int b){ if(!b) return 1; if(b&1) return a*binpow(a,b-1); return (a*a,b/2); // comma operator } Is it possible get a compilation error instead of incorrect, hard to debug code?

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  • StringBuilder/StringBuffer vs. "+" Operator

    - by matt.seil
    I'm reading "Better, Faster, Lighter Java" (by Bruce Tate and Justin Gehtland) and am familiar with the readability requirements in agile type teams, such as what Robert Martin discusses in his clean coding books. On the team I'm on now, I've been told explicitly not to use the "+" operator because it creates extra (and unnecessary) string objects during runtime. But this article: http://www.ibm.com/developerworks/java/library/j-jtp01274.html Written back in '04 talks about how object allocation is about 10 machine instructions. (essentially free) It also talks about how the GC also helps to reduce costs in this environment. What is the actual performance tradeoffs between using "+," "StringBuilder," or "StringBuffer?" (In my case it is StringBuffer only as we are limited to Java 1.4.2.) StringBuffer to me results in ugly, less readable code, as a couple of examples in Tate's book demonstrates. And StringBuffer is thread-synchronized which seems to have its own costs that outweigh the "danger" in using the "+" operator. Thoughts/Opinions?

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  • Overloading generic implicit conversions

    - by raichoo
    Hi I'm having a little scala (version 2.8.0RC1) problem with implicit conversions. Whenever importing more than one implicit conversion the first one gets shadowed. Here is the code where the problem shows up: // containers class Maybe[T] case class Nothing[T]() extends Maybe[T] case class Just[T](value: T) extends Maybe[T] case class Value[T](value: T) trait Monad[C[_]] { def >>=[A, B](a: C[A], f: A => C[B]): C[B] def pure[A](a: A): C[A] } // implicit converter trait Extender[C[_]] { class Wrapper[A](c: C[A]) { def >>=[B](f: A => C[B])(implicit m: Monad[C]): C[B] = { m >>= (c, f) } def >>[B](b: C[B])(implicit m: Monad[C]): C[B] = { m >>= (c, { (x: A) => b } ) } } implicit def extendToMonad[A](c: C[A]) = new Wrapper[A](c) } // instance maybe object maybemonad extends Extender[Maybe] { implicit object MaybeMonad extends Monad[Maybe] { override def >>=[A, B](a: Maybe[A], f: A => Maybe[B]): Maybe[B] = { a match { case Just(x) => f(x) case Nothing() => Nothing() } } override def pure[A](a: A): Maybe[A] = Just(a) } } // instance value object identitymonad extends Extender[Value] { implicit object IdentityMonad extends Monad[Value] { override def >>=[A, B](a: Value[A], f: A => Value[B]): Value[B] = { a match { case Value(x) => f(x) } } override def pure[A](a: A): Value[A] = Value(a) } } import maybemonad._ //import identitymonad._ object Main { def main(args: Array[String]): Unit = { println(Just(1) >>= { (x: Int) => MaybeMonad.pure(x) }) } } When uncommenting the second import statement everything goes wrong since the first "extendToMonad" is shadowed. However, this one works: object Main { implicit def foo(a: Int) = new { def foobar(): Unit = { println("Foobar") } } implicit def foo(a: String) = new { def foobar(): Unit = { println(a) } } def main(args: Array[String]): Unit = { 1 foobar() "bla" foobar() } } So, where is the catch? What am I missing? Regards, raichoo

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  • Problem in using C# generics with method overloading

    - by Siva Chandran
    I am trying to call an overloaded method based on the generic type. I've been doing this in C++ without any pain. But I really don't understand why am not able to do this in C# with generics. Can anybody help me how can I achieve this in C# with generics? class Test<T> { public T Val; public void Do(T val) { Val = val; MainClass.Print(Val); } } class MainClass { public static void Print(UInt16 val) { Console.WriteLine("UInt16: " + val.ToString()); } public static void Print(UInt32 val) { Console.WriteLine("UInt32: " + val.ToString()); } public static void Print(UInt64 val) { Console.WriteLine("UInt64: " + val.ToString()); } public static void Main (string[] args) { Test<UInt16> test = new Test<UInt16>(); test.Do(); } }

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  • Overloading Controller Actions

    - by DaveDev
    Hi Guys I was a bit surprised a few minutes ago when I tried to overload an Action in one of my Controllers I had public ActionResult Get() { return PartialView(/*return all things*/); } I added public ActionResult Get(int id) { return PartialView(/*return 1 thing*/); } .... and all of a sudden neither were working I fixed the issue by making 'id' nullable and getting rid of the other two methods public ActionResult Get(int? id) { if (id.HasValue) return PartialView(/*return 1 thing*/); else return PartialView(/*return everything*/); } and it worked, but my code just got a little bit ugly! Any comments or suggestions? Do I have to live with this blemish on my Controllers? Thanks Dave

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  • Method Overloading for NULL parameter

    - by Phani
    I have added three methods with parameters: public static void doSomething(Object obj) { System.out.println("Object called"); } public static void doSomething(char[] obj) { System.out.println("Array called"); } public static void doSomething(Integer obj) { System.out.println("Array called"); } When I am calling doSomething(null) , then compiler throws error as ambiguous methods. So Is the issue because Integer and char[] methods or Integer and Object methods?

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  • Operator + for matrices in C++

    - by cibercitizen1
    I suppose the naive implementation of a + operator for matrices (2D for instance) in C++ would be: class Matrix { Matrix operator+ (Matrix other) const { Matrix result; // fill result with *this.data plus other.data return result; } } so we could use it like Matrix a; Matrix b; Matrix c; c = a + b; Right? But if matrices are big this is not efficient as we are doing one not-necessary copy (return result). Therefore, If we wan't to be efficient we have to forget the clean call: c = a + b; Right? What would you suggest / prefer ? Thanks.

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  • boost::spirit::karma using the alternatives operator (|) with conditions

    - by Ingemar
    I'm trying to generate a string from my own class called Value using boost::spirit::karma, but i got stuck with this. I've tried to extract my problem into a simple example. I want to generate a String with karma from instances of the following class: class Value { public: enum ValueType { BoolType, NumericType }; Value(bool b) : type_(BoolType), value_(b) {} Value(const double d) : type_(NumericType), value_(d) {}; ValueType type() { return type_; } operator bool() { return boost::get<bool>(value_); } operator double() { return boost::get<double>(value_); } private: ValueType type_; boost::variant<bool, double> value_; }; Here you can see what I'm tying to do: int main() { using karma::bool_; using karma::double_; using karma::rule; using karma::eps; std::string generated; std::back_insert_iterator<std::string> sink(generated); rule<std::back_insert_iterator<std::string>, Value()> value_rule = bool_ | double_; Value bool_value = Value(true); Value double_value = Value(5.0); karma::generate(sink, value_rule, bool_value); std::cout << generated << "\n"; generated.clear(); karma::generate(sink, value_rule, double_value); std::cout << generated << "\n"; return 0; } The first call to karma::generate() works fine because the value is a bool and the first generator in my rule also "consumes" a bool. But the second karma::generate() fails with boost::bad_get because karma tries to eat a bool and calls therefore Value::operator bool(). My next thought was to modify my generator rule and use the eps() generator together with a condition but here i got stuck: value_rule = (eps( ... ) << bool_) | (eps( ... ) << double_); I'm unable to fill the brackets of the eps generator with sth. like this (of course not working): eps(value.type() == BoolType) I've tried to get into boost::phoenix, but my brain seems not to be ready for things like this. Please help me! here is my full example (compiling but not working): main.cpp

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  • Function Overloading

    - by Sanju
    Let us suppose i have these three methods defined: int F1(int, int); int F1(float, float); Float F1(int, int); and i am calling method F1 here: Console.writeline(F1(5,6).ToString())); Which method it will call and why?

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  • C++ conversion operator between types in other libraries

    - by Dave
    For convenience, I'd like to be able to cast between two types defined in other libraries. (Specifically, QString from the Qt library and UnicodeString from the ICU library.) Right now, I have created utility functions in a project namespace: namespace MyProject { const icu_44::UnicodeString ToUnicodeString(const QString& value); const QString ToQString(const icu_44::UnicodeString& value); } That's all well and good, but I'm wondering if there's a more elegant way. Ideally, I'd like to be able to convert between them using a cast operator. I do, however, want to retain the explicit nature of the conversion. An implicit conversion should not be possible. Is there a more elegant way to achieve this without modifying the source code of the libraries? Some operator overload syntax, perhaps?

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  • Operator as and generic classes

    - by abatishchev
    I'm writing .NET On-the-Fly compiler for CLR scripting and want execution method make generic acceptable: object Execute() { return type.InvokeMember(..); } T Execute<T>() { return Execute() as T; /* doesn't work: The type parameter 'T' cannot be used with the 'as' operator because it does not have a class type constraint nor a 'class' constraint */ // also neither typeof(T) not T.GetType(), so on are possible return (T) Execute(); // ok } But I think operator as will be very useful: if result type isn't T method will return null, instead of an exception! Is it possible to do?

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  • Strange behavior when overloading methods in Java

    - by Sep
    I came across this weird (in my opinion) behavior today. Take this simple Test class: public class Test { public static void main(String[] args) { Test t = new Test(); t.run(); } private void run() { List<Object> list = new ArrayList<Object>(); list.add(new Object()); list.add(new Object()); method(list); } public void method(Object o) { System.out.println("Object"); } public void method(List<Object> o) { System.out.println("List of Objects"); } } It behaves the way you expect, printing "List of Objects". But if you change the following three lines: List<String> list = new ArrayList<String>(); list.add(""); list.add(""); you will get "Object" instead. I tried this a few other ways and got the same result. Is this a bug or is it a normal behavior? And if it is normal, can someone explain why? Thanks.

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  • Automatic type conversion in Java?

    - by davr
    Is there a way to do automatic implicit type conversion in Java? For example, say I have two types, 'FooSet' and 'BarSet' which both are representations of a Set. It is easy to convert between the types, such that I have written two utility methods: /** Given a BarSet, returns a FooSet */ public FooSet barTOfoo(BarSet input) { /* ... */ } /** Given a FooSet, returns a BarSet */ public BarSet fooTObar(FooSet input) { /* ... */ } Now say there's a method like this that I want to call: public void doSomething(FooSet data) { /* .. */ } But all I have is a BarSet myBarSet...it means extra typing, like: doSomething(barTOfoo(myBarSet)); Is there a way to tell the compiler that certain types can automatically be cast to other types? I know this is possible in C++ with overloading, but I can't find a way in Java. I want to just be able to type: doSomething(myBarSet); And the compiler knows to automatically call barTOfoo()

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  • Why C# calls different overloaded method for different values of same type?

    - by Fabio Veronez
    Hello all, I have one doubt concerning c# method overloading call resolution. Let's suppose I have the following C# code: enum MyEnum { Value1, Value2 } public void test() { method(0); // this calls method(MyEnum) method(1); // this calls method(object) } public void method(object o) { } public void method(MyEnum e) { } Note that I know how to make it work but I would like to know why for one value of int (0) it calls one method and for another (1) it calls another. It sounds awkward since both values have the same type (int) but they are "linked" for different methods. Ps.: This is my first question here, i'm sorry if I made something wrong. =P

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  • printing using one '\n'

    - by Alex
    I am pretty sure all of you are familiar with the concept of the Big4, and I have several stuffs to do print in each of the constructor, assignment, destructor, and copy constructor. The restriction is this: I CAN'T use more than one newline (e.g., ƒn or std::endl) in any method I can have a method called print, so I am guessing print is where I will put that precious one and only '\n', my problem is that how can the method print which prints different things on each of the element I want to print in each of the Big4? Any idea? Maybe overloading the Big4?

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  • C++ union assignment, is there a good way to do this?

    - by Sqeaky
    I am working on a project with a library and I must work with unions. Specifically I am working with SDL and the SDL_Event union. I need to make copies of the SDL_Events, and I could find no good information on overloading assignment operators with unions. Provided that I can overload the assignment operator, should I manually sift through the union members and copy the pertinent members or can I simply come some members (this seems dangerous to me), or maybe just use memcpy() (this seems simple and fast, but slightly dangerous)? If I can't overload operators what would my best options be from there? I guess I could make new copies and pass around a bunch of pointers, but in this situation I would prefer not to do that. Any ideas welcome!

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  • Which is the better way to simulate optional parameters in Java?

    - by froadie
    I have a Java method that takes 3 parameters, and I'd like it to also have a 4th "optional" parameter. I know that Java doesn't support optional parameters directly, so I coded in a 4th parameter and when I don't want to pass it I pass null. (And then the method checks for null before using it.) I know this is kind of clunky... but the other way is to overload the method which will result in quite a bit of duplication. Which is the better way to implement optional method parameters in Java: using a nullable parameter, or overloading? And why?

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  • PHP __call vs method_exists

    - by neo
    The Project I'm working on contains something like a wrapper for call_user_func(_array) which does some checks before execution. One of those checks is method_exists (In Case the supplied first argument is an instance of a class and the second is a method name) The other is_callable. The function will throw an exception if one of those checks fails. My Code contains an array with function names (setFoo, setBar, etc.) and the php magic function for overloading (__call) which handles setting, replacing and deletion of certain variables (better certain array elements). The Problem: method_exists will return false if the function is not defined. Do I have any chance to get a true if the __call function does proper handling of the request?

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  • How do I create a dynamic method in PHP?

    - by sandelius
    I'm trying to extend my ActiveRecord class with some dynamic methods. I would like to be able to run this from my controller $user = User::find_by_username(param); $user = User::find_by_email(param); I've read a little about overloading and think that's the key. I'v got a static $_attributes in my AR class and I get the table name by pluralizing my model (User = users) in this case. How do I do this? All models extends the ActiveRecord class.

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  • Should I use parentheses in logical statements even where not necessary?

    - by Jeff Bridgman
    Let's say I have a boolean condition a AND b OR c AND d and I'm using a language where AND has a higher order of operation precedent than OR. I could write this line of code: If (a AND b) OR (c AND d) Then ... But really, that's equivalent to: If a AND b OR c AND d Then ... Are there any arguments in for or against including the extraneous parentheses? Does practical experience suggest that it is worth including them for readability? Or is it a sign that a developer needs to really sit down and become confident in the basics of their language?

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