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  • Why doesn't C# allow for global inferred types i.e. using var?

    - by BritishDeveloper
    I know it can't be done since using var can only be done for local variables. I'm just wondering if anyone has a theory why the C# team thought this should be so. e.g. what would be wrong with this: public class SomeClass { var someString = "hello"; //not cool public SomeClass() { var someOtherString = "hello"; //cool } } If someString is initialised then it is obviously a string just like someOtherString. Why is there one rule for local variables and another for globals?

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  • Implicit constructor available for all types derived from Base excepted the current type?

    - by Vincent
    The following code sum up my problem : template<class Parameter> class Base {}; template<class Parameter1, class Parameter2, class Parameter> class Derived1 : public Base<Parameter> { }; template<class Parameter1, class Parameter2, class Parameter> class Derived2 : public Base<Parameter> { public : // Copy constructor Derived2(const Derived2& x); // An EXPLICIT constructor that does a special conversion for a Derived2 // with other template parameters template<class OtherParameter1, class OtherParameter2, class OtherParameter> explicit Derived2( const Derived2<OtherParameter1, OtherParameter2, OtherParameter>& x ); // Now the problem : I want an IMPLICIT constructor that will work for every // type derived from Base EXCEPT // Derived2<OtherParameter1, OtherParameter2, OtherParameter> template<class Type, class = typename std::enable_if</* SOMETHING */>::type> Derived2(const Type& x); }; How to restrict an implicit constructor to all classes derived from the parent class excepted the current class whatever its template parameters, considering that I already have an explicit constructor as in the example code ? EDIT : For the implicit constructor from Base, I can obviously write : template<class OtherParameter> Derived2(const Base<OtherParameter>& x); But in that case, do I have the guaranty that the compiler will not use this constructor as an implicit constructor for Derived2<OtherParameter1, OtherParameter2, OtherParameter> ? EDIT2: Here I have a test : (LWS here : http://liveworkspace.org/code/cd423fb44fb4c97bc3b843732d837abc) #include <iostream> template<typename Type> class Base {}; template<typename Type> class Other : public Base<Type> {}; template<typename Type> class Derived : public Base<Type> { public: Derived() {std::cout<<"empty"<<std::endl;} Derived(const Derived<Type>& x) {std::cout<<"copy"<<std::endl;} template<typename OtherType> explicit Derived(const Derived<OtherType>& x) {std::cout<<"explicit"<<std::endl;} template<typename OtherType> Derived(const Base<OtherType>& x) {std::cout<<"implicit"<<std::endl;} }; int main() { Other<int> other0; Other<double> other1; std::cout<<"1 = "; Derived<int> dint1; // <- empty std::cout<<"2 = "; Derived<int> dint2; // <- empty std::cout<<"3 = "; Derived<double> ddouble; // <- empty std::cout<<"4 = "; Derived<double> ddouble1(ddouble); // <- copy std::cout<<"5 = "; Derived<double> ddouble2(dint1); // <- explicit std::cout<<"6 = "; ddouble = other0; // <- implicit std::cout<<"7 = "; ddouble = other1; // <- implicit std::cout<<"8 = "; ddouble = ddouble2; // <- nothing (normal : default assignment) std::cout<<"\n9 = "; ddouble = Derived<double>(dint1); // <- explicit std::cout<<"10 = "; ddouble = dint2; // <- implicit : WHY ?!?! return 0; } The last line worry me. Is it ok with the C++ standard ? Is it a bug of g++ ?

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  • How do I put all types implementing a certain generic interface in a dictionary?

    - by James Wenday
    Given a particular interface ITarget<T> and a particular type myType, here's how you would determine T if myType implements ITarget<T>. (This code snippet is taken from the answer to an earlier question.) foreach (var i in myType.GetInterfaces ()) if (i.IsGenericType && i.GetGenericTypeDefinition() == typeof(ITarget<>)) return i.GetGenericArguments ()[0] ; However, this only checks a single type, myType. How would I create a dictionary of all such type parameters, where the key is T and the value is myType? I think it would look something like this: var searchTarget = typeof(ITarget<>); var dict = Assembly.GetExecutingAssembly().[???] .Where(t => t.IsGenericType && t.GetGenericTypeDefinition() == searchTarget) .[???]; What goes in the blanks?

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  • How to get global access to enum types in C#?

    - by lala
    This is probably a stupid question, but I can't seem to do it. I want to set up some enums in one class like this: public enum Direction { north, east, south, west }; Then have that enum type accessible to all classes so that some other class could for instance have: Direction dir = north; and be able to pass the enum type between classes: public void changeDirection(Direction direction) { dir = direction; } I thought that setting the enum to public would make this automatically possible, but it doesn't seem to be visible outside of the class I declared the enum in.

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  • Can I change class types in a setter with an object-oriented language?

    - by user214626
    Hello, Here is the problem statement : Calling a setter on the object should result in the object to change to an object of a different class, which language can support this ? Ex. I have a class called "Man" (Parent Class), and two children namely "Toddler" and "Old Man", they are its children because they override a behaviour in Man called as walk.( i.e Toddler sometimes walks using both his hands and legs kneeled down and the Old man uses a stick to support himself). The Man class has a attribute called age, I have a setter on Man,say it is called setAge(int ageValue). I have 3 objects, 2 toddlers, 1 old-Man. (The system is up and running,i guess when we say objects it is obvious) .I will make this call, toddler.setAge(80), I expect the toddler to change to an object of type Old Man. Is this possible.Please suggest. Thanks,

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  • search for a string , and add if it matches

    - by Sharat Chandra
    I have a file that has 2 columns as given below.... 101 6 102 23 103 45 109 36 101 42 108 21 102 24 109 67 and so on...... I want to write a script that adds the values from 2nd column if their corresponding first column matches for example add all 2nd column values if it's 1st column is 101 add all 2nd column values if it's 1st colummn is 102 add all 2nd column values if it's 1st colummn is 103 and so on ... i wrote my script like this , but i'm not getting the correct result awk '{print $1}' data.txt > col1.txt while read line do awk ' if [$1 == $line] sum+=$2; END {print "Sum for time stamp", $line"=", sum}; sum=0' data.txt done < col1.txt

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  • How do I drop a foerign key in mssql?

    - by mmattax
    I have created a foreign key (in mssql / tsql) by: alter table company add CountryID varchar(3); alter table company add constraint Company_CountryID_FK foreign key(CountryID) references Country; I then run this query: alter table company drop column CountryID; and I get this error: Msg 5074, Level 16, State 4, Line 2 The object 'Company_CountryID_FK' is dependent on column 'CountryID'. Msg 4922, Level 16, State 9, Line 2 ALTER TABLE DROP COLUMN CountryID failed because one or more objects access this column. I have tried this, yet it does not seem to work: alter table company drop foreign key Company_CountryID_FK; alter table company drop column CountryID; What do I need to do to drop the CountryID column? Thanks.

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  • How should I return different types in a method based on the value of a string in Java?

    - by Siracuse
    I'm new to Java and I have come to having the following problem: I have created several classes which all implement the interface "Parser". I have a JavaParser, PythonParser, CParser and finally a TextParser. I'm trying to write a method so it will take either a File or a String (representing a filename) and return the appropriate parser given the extension of the file. Here is some psuedo-code of what I'm basically attempting to do: public Parser getParser(String filename) { String extension = filename.substring(filename.lastIndexOf(".")); switch(extension) { case "py": return new PythonParser(); case "java": return new JavaParser(); case "c": return new CParser(); default: return new TextParser(); } } In general, is this the right way to handle this situation? Also, how should I handle the fact that Java doesn't allow switching on strings? Should I use the .hashcode() value of the strings? I feel like there is some design pattern or something for handling this but it eludes me. Is this how you would do it?

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  • How does cast in C#/.NET 3.5 work for types with '?'

    - by Inez
    This is my code which works public decimal? Get() { var res = ... return res.Count() > 0 ? res.First() : (decimal?) null; } and this one doesn't work public decimal? Get() { var res = ... return res.Count() > 0 ? res.First() : null; } giving the compiler error: Error 1 Type of conditional expression cannot be determined because there is no implicit conversion between 'decimal' and '<null>' I wonder why? any ideas?

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  • Python CSV file processing

    - by kingwarchief
    I just got introduced to python, the first language I get to learn, and I have this question below: I have an excel based CSV file with two columns (or rows, Pythonically) that I am working on. What I need to do is to perform some operations so that I can compare the two data entries in each 'row'. To be more precise, one column has constant numbers all the way down, whereas the other column varies. So I need to count the number of times the varying column data entry values crosses the constant value on the other column. For example: Varying Column; Constant Column 24 25 26 25 crosses 27 25 26 25 25.5 25 23 25 crossed 26 25 crossed So in this case the number of times there is a cross

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  • Is there a way to specify different width to columns in CSS3?

    - by hairbymaurice
    Hello I would like to use css3 to present a two column layout. The markup i am using is this <div style="-webkit-column-count: 2;-webkit-column-rule: 1px solid black;-webkit-column-width: 80px;margin-left:20px;margin-top:20px;" > <div id="picturebox" style="">picture box</div> <div id="nme">name</div> </div> Is there a way to give one column a width of 20px and one column a width of say 80px? Thanks Hairby

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  • Nonstatic conversion functions; Casting different types, e.g. DirectX vector to OpenGL vector

    - by Markus
    I am currently working on a game "engine" that needs to move values between a 3D engine, a physics engine and a scripting language. Since I need to apply vectors from the physics engine to 3D objects very often and want to be able to control both the 3D, as well as the physics objects through the scripting system, I need a mechanism to convert a vector of one type (e.g. vector3d<float>) to a vector of the other type (e.g. btVector3). Unfortunately I can make no assumptions on how the classes/structs are laid out, so a simple reinterpret_cast probably won't do. So the question is: Is there some sort of 'static'/non-member casting method to achieve basically this: vector3d<float> operator vector3d<float>(btVector3 vector) { // convert and return } btVector3 operator btVector3(vector3d<float> vector) { // convert and return } Right now this won't compile since casting operators need to be member methods. (error C2801: 'operator foo' must be a non-static member)

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  • How do you override operator == when using interfaces instead of actual types?

    - by RickL
    I have some code like this: How should I implement the operator == so that it will be called when the variables are of interface IMyClass? public class MyClass : IMyClass { public static bool operator ==(MyClass a, MyClass b) { if (ReferenceEquals(a, b)) return true; if ((Object)a == null || (Object)b == null) return false; return false; } public static bool operator !=(MyClass a, MyClass b) { return !(a == b); } } class Program { static void Main(string[] args) { IMyClass m1 = new MyClass(); IMyClass m2 = new MyClass(); MyClass m3 = new MyClass(); MyClass m4 = new MyClass(); Console.WriteLine(m1 == m2); // does not go into custom == function. why not? Console.WriteLine(m3 == m4); // DOES go into custom == function } }

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  • Removing certain characters in all rows that match a regex?

    - by user001
    I'd like to change {foo, {bar}, foobar} to {foo, bar, foobar} in all rows that match '{.*{'. I.e. remove all curly braces { and } except the outer most pair. So doing mysql -h $H -u $U -p$P $DB -B -e "SELECT id FROM t WHERE col REGEXP '{.*{'" > bad.txt selects all the rows that will need this substitution. How do I make this substitution very quickly? EDIT: Could I do it by update table set column = REPLACE(column,'{',''); Then restore the out most pair update table set column = REPLACE(column,'^','{'); update table set column = REPLACE(column,'$','}');

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  • How to discovering types exported by OSGi bundle without installing/activating ?

    - by mP
    Basically i want to discover if a jar implements any number of interfaces wihtout activating or starting the bundle. Is it possible to read the meta data from the meta-inf from an API just like the container does but without activating a bundle ? I want to use OSGi to support plugins of which numerous interfaces will be published and i would like to know which interfaces are implemented by a bundle when the user uploads without activating the bundle etc.

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  • Function templates for arbitrary STL containers containing arbitrary types.

    - by Chad Brewbaker
    I have an arbitrary STL container C, which contains elements of an arbitrary type T. I want to create an std::vector that has a copy of all the elements. What is the cleanest way to do this? template <typename C> void myfunction(C container){ /*Derive the type T of elements within the container*/ std::vector<T> mystack; /* Iterate over container and push_back() the elements into mystack*/ }

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  • Relation to multiple tables of different types for rating?

    - by Tronic
    i have a table structure like this Products Team Images and want to implement a rating/commenting-feature, where users can rate each entry of all tables. what's the best way to make a single rating table? e.g. a user votes a a product and a team entry, and it should be possible to get alle these entries from a single table. what kind of table-structure is best for this purpose? i hope, my questions is clear enough :/ thanks in advance!

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  • What types of objects should the ViewModel reference in the MVVM pattern?

    - by Blanthor
    I've seen quite a few examples of MVVM. I can see that the View should reference the ViewModel. I've seen recently an example of a ViewModel referencing a View, which seems wrong to me, as it would result in tighter coupling. Given that ViewModel is often described as an intermediary between the View and the Model, is there more to the ViewModel than a facade to domain objects? I hope I used the term "facade" correctly here.

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  • Can I make the compiler and the CLR ignore non implemented interfaces on my types?

    - by Thiado de Arruda
    I would like to define a type implementing a certain interface, however I would only implement it in a proxy at runtime. I can see two obstacles in this scenario : 1-Make the compiler ignore non implemented interfaces. 2-Make the CLR ignore(or at least delay) the TypeLoadException with the following description : "Method SOMEMETHOD in type SOMETYPE from assembly SOMEASSEMBLY does not have an implementation." Is something like this possible?

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  • Using typedefs (or #defines) on built in types - any sensible reason?

    - by jb
    Well I'm doing some Java - C integration, and throught C library werid type mappings are used (theres more of them;)): #define CHAR char /* 8 bit signed int */ #define SHORT short /* 16 bit signed int */ #define INT int /* "natural" length signed int */ #define LONG long /* 32 bit signed int */ typedef unsigned char BYTE; /* 8 bit unsigned int */ typedef unsigned char UCHAR; /* 8 bit unsigned int */ typedef unsigned short USHORT; /* 16 bit unsigned int */ typedef unsigned int UINT; /* "natural" length unsigned int*/ Is there any legitimate reason not to use them? It's not like char is going to be redefined anytime soon. I can think of: Writing platform/compiler portable code (size of type is underspecified in C/C++) Saving space and time on embedded systems - if you loop over array shorter than 255 on 8bit microprocessor writing: for(uint8_t ii = 0; ii < len; ii++) will give meaureable speedup.

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  • 3 fixed Columns (header and footer) using DIVs, NO Absolute DIVs, IE friendly, ALL columns stretch e

    - by Phillip Schein
    Left to right, Col1 id 560px wide with 10 px padding, middle column, 250px wide with 5px padding and Col3 (siderbar) is 200px wide with 3px padding. Background coloR, no matter text length in any column should stretch vertically equal. No javascript (jQuery workarounds) to make it work. It needs to be pure Semantic Markup with CSS. Each Column should have a nested column of color were content will go. Column 1 should be SEO prominant which means the highest nested column for Google and other Search Engines to crawl. I have used 'The Holy Grail" layout, articles at "A List Apart" and these solution are so convoluted that they push the main columns left and than the nested columns push them with padding back right. This is crazy! I try to adjust these examples, but they're not editable by just adjusting a width in the CSS or the padding, etc. Can you please help me?

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  • How cast in c#/.net 3.5 works? for types with '?'

    - by Inez
    This is my code which works public decimal? Get() { var res = ... return res.Count() > 0 ? res.First() : (decimal?) null; } and this one doesn't work public decimal? Get() { var res = ... return res.Count() > 0 ? res.First() : null; } giving the compilator error: Error 1 Type of conditional expression cannot be determined because there is no implicit conversion between 'decimal' and '' I wonder why? any ideas?

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