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  • Returning object from function

    - by brainydexter
    I am really confused now on how and which method to use to return object from a function. I want some feedback on the solutions for the given requirements. Scenario A: The returned object is to be stored in a variable which need not be modified during its lifetime. Thus, const Foo SomeClass::GetFoo() { return Foo(); } invoked as: someMethod() { const Foo& l_Foo = someClassPInstance->GetFoo(); //... } Scneraio B: The returned object is to be stored in a variable which will be modified during its lifetime. Thus, void SomeClass::GetFoo(Foo& a_Foo_ref) { a_Foo_ref = Foo(); } invoked as: someMethod() { Foo l_Foo; someClassPInstance-GetFoo(l_Foo); //... } I have one question here: Lets say that Foo cannot have a default constructor. Then how would you deal with that in this situation, since we cant write this anymore: Foo l_Foo Scenario C: Foo SomeClass::GetFoo() { return Foo(); } invoked as: someMethod() { Foo l_Foo = someClassPInstance->GetFoo(); //... } I think this is not the recommended approach since it would incur constructing extra temporaries. What do you think ? Also, do you recommend a better way to handle this instead ?

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  • Initializing objects on the fly

    - by pocoa
    I have a vector called players and a class called Player. And what I'm trying to do is to write: players.push_back(Player(name, Weapon(bullets))); So I want to be able to create players in a loop. But I see an error message says "no matching function for call Player::Player..." Then I've changed that to: Weapon w(bullets); Player p(name, w); players.push_back(p); Here is my Player definition: class Player { public: Player(string &name, Weapon &weapon); private string name; Weapon weapon; } I'm just trying to learn what is the difference between these definitions. And is this the right way to pass an object to an object constructor. Note: These are not my actual class definitions. I'm just trying to learn something about object oriented programming in C++ with coding it. I mean I know that Weapon should be initialized in Player :)

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  • Javascript instanceof & typeof in GWT (JSNI)

    - by rybz
    Hi, I've encountered an curious problem while trying to use some objects through JSNI in GWT. Let's say we have javscript file with the function defined: test.js: function test(arg){ var type = typeof(arg); if (arg instanceof Array) alert('Array'); if (arg instanceof Object) alert('Object'); if (arg instanceof String) alert('String'); } And the we want to call this function user JSNI: public static native void testx()/ *-{ $wnd.test( new Array(1, 2, 3) ); $wnd.test( [ 1, 2, 3 ] ); $wnd.test( {val:1} ); $wnd.test( "Some text" ); }-*/; The questions are: why instanceof instructions will always return false? why typeof will always return "object" ? how to pass these objects so that they were recognized properly?

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  • Using the word "you" in an user manual

    - by yan bellavance
    I am writing a user manual and I have come to a discussion with a colleague. He says I cannot use the word "you" anywhere in the manual. Now I remember something about this at school but that was not for writing procedures. Also, doing some googling I observed that most tutorials where using it a lot. I would prefer using it but only if this is considered good practice. what do you think?

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  • Implicit parameter in Scalaz

    - by Thomas Jung
    I try to find out why the call Ø in scalaz.ListW.<^> works def <^>[B: Zero](f: NonEmptyList[A] => B): B = value match { case Nil => Ø case h :: t => f(Scalaz.nel(h, t)) } My minimal theory is: trait X[T]{ def y : T } object X{ implicit object IntX extends X[Int]{ def y = 42 } implicit object StringX extends X[String]{ def y = "y" } } trait Xs{ def ys[T](implicit x : X[T]) = x.y } class A extends Xs{ def z[B](implicit x : X[B]) : B = ys //the call Ø } Which produces: import X._ scala> new A().z[Int] res0: Int = 42 scala> new A().z[String] res1: String = y Is this valid? Can I achieve the same result with fewer steps?

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  • how do I initialize a float to its max/min value?

    - by Faken
    How do I hard code an absolute maximum or minimum value for a float or double? I want to search out the max/min of an array by simply iterating through and catching the largest. There are also positive and negative infinity for floats, should I use those instead? If so, how do I denote that in my code?

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  • Undetermined type conversion in VB.NET 2008

    - by user337501
    I figured this would be a quick google, but extensive searching hasnt yielded any results. Everything about type conversion seems to dance around this concept. I want to get the type of variable "a", and make a new variable named "b" of that type. Otherwise I could have "a" as a type already declared and "b" simply as an Object, then try to cast "b" to the type of "a". Dim a As Integer Dim b As Whatever a Is OR TryCast(b, Whatever a Is) I would also like to make the conversion using a variable representation of the type, but cant find info on how to do that either. Sorta like: Dim a As Integer Dim b As Object Dim t As Type t = a.GetType() TryCast(b, t) Realizing I'm completely misusing TryCast here, I'm mostly trying to get my goal across. I figured it would be an easy quick thing to do but I cant really find any specific info on it. Any ideas?

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  • how to write a constructor...

    - by Nima
    is that correct to write a constructor like this? class A { A::A(const A& a) { .... } }; if yes, then is it correct to invoke it like this: A* other; ... A* instance = new A(*(other)); if not, what do you suggest? Thanks

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  • Function with parameter type that has a copy-constructor with non-const ref chosen?

    - by Johannes Schaub - litb
    Some time ago I was confused by the following behavior of some code when I wanted to write a is_callable<F, Args...> trait. Overload resolution won't call functions accepting arguments by non-const ref, right? Why doesn't it reject in the following because the constructor wants a Test&? I expected it to take f(int)! struct Test { Test() { } // I want Test not be copyable from rvalues! Test(Test&) { } // But it's convertible to int operator int() { return 0; } }; void f(int) { } void f(Test) { } struct WorksFine { }; struct Slurper { Slurper(WorksFine&) { } }; struct Eater { Eater(WorksFine) { } }; void g(Slurper) { } void g(Eater) { } // chooses this, as expected int main() { // Error, why? f(Test()); // But this works, why? g(WorksFine()); } Error message is m.cpp: In function 'int main()': m.cpp:33:11: error: no matching function for call to 'Test::Test(Test)' m.cpp:5:3: note: candidates are: Test::Test(Test&) m.cpp:2:3: note: Test::Test() m.cpp:33:11: error: initializing argument 1 of 'void f(Test)' Can you please explain why one works but the other doesn't?

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  • Sharing common class in wcf project

    - by Saint
    class MyCommonClass { //properties } This class should be accessible in service project wcf-client project the other for which they are references. In this common project I can't generate servicereferences. I think, I could don't generate MyCommonClass in ServiceReferences but how to mark class to be nonserializable? In properties there's IgnoreDataMemberAttribute. I tried also reuse MyCommonClass type located in common project, but it is still generated

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  • Delphi constants and references

    - by Sambatyon
    I want to pass constant references to functions in delphi, so I am sure that the referenced object won't change and to save time and memory. So I want to declare a function like function foo(var const Value : Bar) : Boolean; however this is not allowed. I thought constant values would be automatically sent as references. However I found out that it is not the case (getting the address of an object before sending it to the function gives me $12F50C and the address of the same object inside the function is $12F564) What can I do to send constant references?

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  • "Home" of Javascript similar to python.org?

    - by drewk
    Perl, Ruby, Python, Javascript / ecmascript, PHP are all similar in the sense of being open source, open documentation, multi-platform, etc. Perl has http://www.perl.org Ruby has http://www.ruby-lang.org Python has http://www.python.org PHP has http://php.net Is there a "home" for javascript in the same sense as these other languages? When I say "home" I mean the go-to place for official documentation, specifications, source code of the language, examples, etc.

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  • Perfect hash in Scala.

    - by Lukasz Lew
    I have some class C: class C (...) { ... } I want to use it to index an efficient map. The most efficient map is an Array. So I add a "global" "static" counter in companion object to give each object unique id: object C { var id_counter = 0 } In primary constructor of C, with each creation of C I want to remember global counter value and increase it. Question 1: How to do it? Now I can use id in C objects as perfect hash to index array. But array does not preserve type information like map would, that a given array is indexed by C's id. Question 2: Is it possible to have it with type safety?

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  • Newbie C# Question about float/int/text type formatting

    - by user563501
    Hey everybody, I'm a total C# newb with a light (first year CS) background in Python. I wrote a console program in Python for doing marathon pace running calculations and I'm trying to figure out the syntax for this in C# using Visual Studio 2010. Here's a chunk of what I've got so far: string total_seconds = ((float.Parse(textBox_Hours.Text) * 60 * 60) + (float.Parse(textBox_Minutes.Text) * 60) + float.Parse(textBox_Seconds.Text)).ToString(); float secs_per_unit = ((float)(total_seconds) / (float)(textBox_Distance.Text)); float mins_per_unit = (secs_per_unit / 60); string pace_mins = (int)mins_per_unit.ToString(); string pace_secs = (float.Parse(mins_per_unit) - int.Parse(mins_per_unit) * 60).ToString(); textBox_Final_Mins.Text = pace_mins; textBox_Final_Secs.Text = pace_mins; Imagine you have a running pace of 8 minutes and 30 seconds per mile. secs_per_unit would be 510, mins_per_unit would be 8.5. pace_mins would simply be 8 and pace_secs would be 30. In Python I'd just convert variables from a float to a string to get 8 instead of 8.5, for example; hopefully the rest of the code gives you an idea of what I've been doing. Any input would be appreciated.

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  • Data Structures for Junior Java Developer

    - by user1639637
    Ok,still learning Arrays. I wrote this code which fills the array named "rand" with random numbers between 0 and 1( exclusive). I want to start learning Complexity. the For loop executes n times (100 times) ,every time it takes O(1) time,so the worse case scenario is O(n),am I right? Also,I used ArrayList to store the 100 elements and I imported "Collections" and used Collections.sort() method to sort the elements. import java.util.Arrays; public class random { public static void main(String args[]) { double[] rand=new double[10]; for(int i=0;i<rand.length;i++) { rand[i]=(double) Math.random(); System.out.println(rand[i]); } Arrays.sort(rand); System.out.println(Arrays.toString(rand)); } } ArrayList: import java.util.ArrayList; import java.util.Collections; public class random { public static void main(String args[]) { ArrayList<Double> MyArrayList=new ArrayList<Double>(); for(int i=0;i<100;i++) { MyArrayList.add(Math.random()); } Collections.sort(MyArrayList); for(int j=0;j<MyArrayList.size();j++) { System.out.println(MyArrayList.get(j)); } } }

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  • LINQ Group By to project into a non-anonymous type?

    - by vikp
    Hi, I have the following LINQ example: var colorDistribution = from product in ctx.Products group product by product.Color into productColors select new { Color = productColors.Key, Count = productColors.Count() }; All this works and makes perfect sense. What I'm trying to achieve is to group by into a strong type instead of anonymous type. For example I have a ProductColour class and I would like to Group into a List<ProductColour> Is this possible? Thank you

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  • Is there any way to add references without recompiling in .NET?

    - by Jader Dias
    I am using a IoC Container (Castle Windsor) to instantiate classes accordingly to the configuration file. If I want to add classes from a new dll that didn't exist when I compiled the project, there is any way to do that without recompiling? Edit: As this project is a Service Host for WCF service, and the classes that I want to include after compilation are WCF Services I would like also to know if I can include endpoint information about new services without recompiling.

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  • Best way to determine variable type and treat each one differently in F#

    - by James Black
    I have a function that will create a select where clause, but right now everything has to be a string. I would like to look at the variable passed in and determine what type it is and then treat it properly. For example, numeric values don't have single quotes around them, option type will either be null or have some value and boolean will actually be zero or one. member self.BuildSelectWhereQuery (oldUser:'a) = let properties = List.zip oldUser.ToSqlValuesList sqlColumnList let init = false, new StringBuilder() let anyChange, (formatted:StringBuilder) = properties |> Seq.fold (fun (anyChange, sb) (oldVal, name) -> match(anyChange) with | true -> true, sb.AppendFormat(" AND {0} = '{1}'", name, oldVal) | _ -> true, sb.AppendFormat("{0} = '{1}'", name, oldVal) ) init formatted.ToString() Here is one entity: type CityType() = inherit BaseType() let mutable name = "" let mutable stateId = 0 member this.Name with get() = name and set restnameval=name <- restnameval member this.StateId with get() = stateId and set stateidval=stateId <- stateidval override this.ToSqlValuesList = [this.Name; this.StateId.ToString()] So, if name was some other value besides a string, or stateId can be optional, then I have two changes to make: How do I modify ToSqlValuesList to have the variable so I can tell the variable type? How do I change my select function to handle this? I am thinking that I need a new function does the processing, but what is the best FP way to do this, rather than using something like typeof?

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  • Output is different for R-value and L-value. Why?

    - by Leonid Volnitsky
    Can someone explain to me why output for R-value is different from L-value? #include <iostream> #include <vector> using namespace std; template<typename Ct> struct ct_wrapper { Ct&& ct; // R or L ref explicit ct_wrapper(Ct&& ct) : ct(std::forward<Ct>(ct)) { std::cout << this->ct[1];}; }; int main() { // L-val vector<int> v{1,2,3}; ct_wrapper<vector<int>&> lv(v); cout << endl << lv.ct[0] << lv.ct[1] << lv.ct[2] << endl; // R-val ct_wrapper<vector<int>&&> rv(vector<int>{1,2,3}); cout << endl << rv.ct[0] << rv.ct[1] << rv.ct[2] << endl; } Output (same for gcc48 and clang32): 2 123 2 003

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  • Access to an inner type

    - by sohum
    A colleague of mine posted a question on an internal forum which got me thinking about whether this was possible through C#. Basically, he's got an interface as follows: public interface IProvider<T> { T GetT(); } Is it possible to use something that implements that interface as a type parameter to another generic class and have access to the type T without re-specifying it? For example: public class Foo<P> where P : IProvider<T> { P p; T GetInnerT() { return p.GetT(); } } This does not compile, because the type T is not defined and hence can't be used as a parameter for IProvider. Is something like this even possible? Just curious!

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