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  • Confusion for mime files: magic, magic.mgc, magic.mime

    - by Florence Foo
    I'm using Ubuntu. I'm trying to use ruby gem 'shared-mime-info' for an application I'm writing. I understand that magic.mgc is a compiled version of magic file which has magic number definitions for the different file types. BUT I don't understand why is it /usr/share/mime/magic is in binary format instead of just normal text file with each parameters separated by white space like everywhere else I'm finding on the internet when it's referencing this file? The /usr/share/mime/magic has the word 'MIME-Magic' at the beginning of the file and prioritize the rest of the stuff like. So it doesn't look like magic.mgc at all. [100:application/vnd.scribus] >1=^@^KSCRIBUSUTF8 [90:application/vnd.stardivision.writer] >2089=^@ shared-mime-info seems to want a magic file in the binary non compiled format as above and I wanted to add definition for DOCX but how does one update or generate this file without using a hex editor? There is a reference to the magic file I found at: http://standards.freedesktop.org/shared-mime-info-spec/shared-mime-info-spec-latest.html And it mention this file is updated with update-mime-database but what if I just want to add some new entry to it. hex editor? Anyway I ended up using hexer to make a new magic file in ~/.local/share/mime/ with only the entry I wanted to add and the MIME-Magic header. Seems to work (assuming I will ever deal with docx for now). 00000000: 4d 49 4d 45 2d 4d 61 67 69 63 00 0a 5b 36 30 3a MIME-Magic..[60: 00000010: 61 70 70 6c 69 63 61 74 69 6f 6e 2f 76 6e 64 2e application/vnd. 00000020: 6f 70 65 6e 78 6d 6c 66 6f 72 6d 61 74 73 2d 6f openxmlformats-o 00000030: 66 66 69 63 65 64 6f 63 75 6d 65 6e 74 2e 77 6f fficedocument.wo 00000040: 72 64 70 72 6f 63 65 73 73 69 6e 67 6d 6c 2e 64 rdprocessingml.d 00000050: 6f 63 75 6d 65 6e 74 5d 0a 3e 30 3d 00 08 50 4b ocument].>0=..PK 00000060: 03 04 14 00 06 00 0a -- -- -- -- -- -- -- -- -- .......---------

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  • C# 4.0: Covariance And Contravariance In Generics

    - by Paulo Morgado
    C# 4.0 (and .NET 4.0) introduced covariance and contravariance to generic interfaces and delegates. But what is this variance thing? According to Wikipedia, in multilinear algebra and tensor analysis, covariance and contravariance describe how the quantitative description of certain geometrical or physical entities changes when passing from one coordinate system to another.(*) But what does this have to do with C# or .NET? In type theory, a the type T is greater (>) than type S if S is a subtype (derives from) T, which means that there is a quantitative description for types in a type hierarchy. So, how does covariance and contravariance apply to C# (and .NET) generic types? In C# (and .NET), variance applies to generic type parameters and not to the resulting generic type. A generic type parameter is: covariant if the ordering of the generic types follows the ordering of the generic type parameters: Generic<T> = Generic<S> for T = S. contravariant if the ordering of the generic types is reversed from the ordering of the generic type parameters: Generic<T> = Generic<S> for T = S. invariant if neither of the above apply. If this definition is applied to arrays, we can see that arrays have always been covariant because this is valid code: object[] objectArray = new string[] { "string 1", "string 2" }; objectArray[0] = "string 3"; objectArray[1] = new object(); However, when we try to run this code, the second assignment will throw an ArrayTypeMismatchException. Although the compiler was fooled into thinking this was valid code because an object is being assigned to an element of an array of object, at run time, there is always a type check to guarantee that the runtime type of the definition of the elements of the array is greater or equal to the instance being assigned to the element. In the above example, because the runtime type of the array is array of string, the first assignment of array elements is valid because string = string and the second is invalid because string = object. This leads to the conclusion that, although arrays have always been covariant, they are not safely covariant – code that compiles is not guaranteed to run without errors. In C#, the way to define that a generic type parameter as covariant is using the out generic modifier: public interface IEnumerable<out T> { IEnumerator<T> GetEnumerator(); } public interface IEnumerator<out T> { T Current { get; } bool MoveNext(); } Notice the convenient use the pre-existing out keyword. Besides the benefit of not having to remember a new hypothetic covariant keyword, out is easier to remember because it defines that the generic type parameter can only appear in output positions — read-only properties and method return values. In a similar way, the way to define a type parameter as contravariant is using the in generic modifier: public interface IComparer<in T> { int Compare(T x, T y); } Once again, the use of the pre-existing in keyword makes it easier to remember that the generic type parameter can only be used in input positions — write-only properties and method non ref and non out parameters. Because covariance and contravariance apply only to the generic type parameters, a generic type definition can have both covariant and contravariant generic type parameters in its definition: public delegate TResult Func<in T, out TResult>(T arg); A generic type parameter that is not marked covariant (out) or contravariant (in) is invariant. All the types in the .NET Framework where variance could be applied to its generic type parameters have been modified to take advantage of this new feature. In summary, the rules for variance in C# (and .NET) are: Variance in type parameters are restricted to generic interface and generic delegate types. A generic interface or generic delegate type can have both covariant and contravariant type parameters. Variance applies only to reference types; if you specify a value type for a variant type parameter, that type parameter is invariant for the resulting constructed type. Variance does not apply to delegate combination. That is, given two delegates of types Action<Derived> and Action<Base>, you cannot combine the second delegate with the first although the result would be type safe. Variance allows the second delegate to be assigned to a variable of type Action<Derived>, but delegates can combine only if their types match exactly. If you want to learn more about variance in C# (and .NET), you can always read: Covariance and Contravariance in Generics — MSDN Library Exact rules for variance validity — Eric Lippert Events get a little overhaul in C# 4, Afterward: Effective Events — Chris Burrows Note: Because variance is a feature of .NET 4.0 and not only of C# 4.0, all this also applies to Visual Basic 10.

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  • Mission critical embedded language

    - by Moe
    Maybe the question sounds a bit strange, so i'll explain a the background a little bit. Currently i'm working on a project at y university, which will be a complete on-board software for an satellite. The system is programmed in c++ on top of a real-time operating system. However, some subsystems like the attitude control system and the fault detection and a space simulation are currently only implemented in Matlab/Simulink, to prototype the algorithms efficiently. After their verification, they will be translated into c++. The complete on-board software grew very complex, and only a handful people know the whole system. Furthermore, many of the students haven't program in c++ yet and the manual memory management of c++ makes it even more difficult to write mission critical software. Of course the main system has to be implemented in c++, but i asked myself if it's maybe possible to use an embedded language to implement the subsystem which are currently written in Matlab. This embedded language should feature: static/strong typing and compiler checks to minimize runtime errors small memory usage, and relative fast runtime attitude control algorithms are mainly numerical computations, so a good numeric support would be nice maybe some sort of functional programming feature, matlab/simulink encourage you to use it too I googled a bit, but only found Lua. It looks nice, but i would not use it in mission critical software. Have you ever encountered a situation like this, or do you know any language, which could satisfies the conditions? EDIT: To clarify some things: embedded means it should be able to embed the language into the existing c++ environment. So no compiled languages like Ada or Haskell ;)

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  • Question about casting a class in Java with generics

    - by Florian F
    In Java 6 Class<? extends ArrayList<?>> a = ArrayList.class; gives and error, but Class<? extends ArrayList<?>> b = (Class<? extends ArrayList<?>>)ArrayList.class; gives a warning. Why is (a) an error? What is it, that Java needs to do in the assignment, if not the cast shown in (b)? And why isn't ArrayList compatible with ArrayList? I know one is "raw" and the other is "generic", but what is it you can do with an ArrayList and not with an ArrayList, or the other way around?

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  • Matrix Pattern Recognition Algorithm

    - by Andres
    I am designing a logic analyzer and I would like to implement some Matrix Algorithm. I have several channels each one represented by a row in the matrix and every element in the column would be the state, for example: Channel 1 1 0 0 1 0 1 1 0 1 Channel 2 1 1 0 1 1 0 0 1 1 Channel 3 0 1 0 1 1 0 1 0 0 Channel 4 0 0 1 0 0 1 0 0 1 I would like to detect a pattern inside my matrix for example, detect if exist and where the sub-matrix or pattern: 1 0 1 1 I think it can be accomplished testing element by element but I think there should be a better way of doing it. Is there any Java API or any way to do it ? If there is a API ARM optimized for NEON instructions would be great also but not mandatory. Thank you very much in advance.

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  • Firefox application associations not working

    - by Pavlos G.
    No matter what changes i make to file associations (actions) in the 'Applications' tab in firefox, they're totally ignored. For example, i set .wmv and .avi files to open with 'smplayer' but when i download a file and double-click on it (through the 'Downloads' window), it keeps opening with Totem player. I've tried to delete and recreate mimetypes.rdf but that didn't help. Any ideas on what else should i check?

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  • When should a method of a class return the same instance after modifying itself?

    - by modiX
    I have a class that has three methods A(), B() and C(). Those methods modify the own instance. While the methods have to return an instance when the instance is a separate copy (just as Clone()), I got a free choice to return void or the same instance (return this;) when modifying the same instance in the method and not returning any other value. When deciding for returning the same modified instance, I can do neat method chains like obj.A().B().C();. Would this be the only reason for doing so? Is it even okay to modify the own instance and return it, too? Or should it only return a copy and leave the original object as before? Because when returning the same modified instance the user would maybe admit the returned value is a copy, otherwise it would not be returned? If it's okay, what's the best way to clarify such things on the method?

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  • C# return variables

    - by pb01
    In a debate regarding return variables, some members of the team prefer a method to return the result directly to the caller, whereas others prefer to declare a return variable that is then returned to the caller (see code examples below) The argument for the latter is that it allows a developer that is debugging the code to find the return value of the method before it returns to the caller thereby making the code easier to understand: This is especially true where method calls are daisy-chained. Are there any guidelines as to which is the most efficient and/or are there any other reasons why we should adopt one style over another? Thanks private bool Is2(int a) { return a == 2; } private bool Is3(int a) { var result = a == 3; return result; }

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  • Optimization ended up in casting an object at each method call

    - by Aybe
    I've been doing some optimization for the following piece of code : public void DrawLine(int x1, int y1, int x2, int y2, int color) { _bitmap.DrawLineBresenham(x1, y1, x2, y2, color); } After profiling it about 70% of the time spent was in getting a context for drawing and disposing it. I ended up sketching the following overload : public void DrawLine(int x1, int y1, int x2, int y2, int color, BitmapContext bitmapContext) { _bitmap.DrawLineBresenham(x1, y1, x2, y2, color, bitmapContext); } Until here no problems, all the user has to do is to pass a context and performance is really great as a context is created/disposed one time only (previously it was a thousand times per second). The next step was to make it generic in the sense it doesn't depend on a particular framework for rendering (besides .NET obvisouly). So I wrote this method : public void DrawLine(int x1, int y1, int x2, int y2, int color, IDisposable bitmapContext) { _bitmap.DrawLineBresenham(x1, y1, x2, y2, color, (BitmapContext)bitmapContext); } Now every time a line is drawn the generic context is casted, this was unexpected for me. Are there any approaches for fixing this design issue ? Note : _bitmap is a WriteableBitmap from WPF BitmapContext is from WriteableBitmapEx library DrawLineBresenham is an extension method from WriteableBitmapEx

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  • Web browser downloads only open target folders - cannot open files

    - by Pavlos G.
    After installing xubuntu packages in order to check xfce, I reverted back to gnome2. During the first login, I noticed that thunar was now selected as the default file manager. Preferred applications menu is also missing now, so I could not set nautilus as the default. I removed all the xubuntu packages (including thunar) and then when I tried to open a folder, I was asked to select the default file manager - that's how I got nautilus back. The next problem I'm now facing has to do with the downloaded files from web browsers: Open and Open containing folder options produce exactly the same result. If I double-click on a file, it'll just open the containing folder, instead of opening the file with it's associated application (e.g. libreoffice writer for .doc,.odt, smplayer for .avi,.wmv, etc). The problem happens both in Firefox and Chrome. Through nautilus, all files open correctly. Up until now I've tried the following: Delete/recreate mimeTypes.rdf in my FF profile Create a new profile in FF Delete/recreate ~/.local/share/applications/mimeapps.list Already checked this similar article None of them worked. Any ideas on the issue would be appreciated.

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  • Loose typing not applied to objects

    - by TecBrat
    I have very little experience working with classes and object. I work in a loosely typed language, PHP. I was working with a SimpleXML object and ran into a problem where I was trying to do math with an element of that object like $results->ProductDetail->{'Net'.$i}; If I echoed that value, I'd get 0.53 but when I tried to do math with it, it was converted to 0 Is there a reason that a loosely typed language would not recognize that as a float and handle it as such? Why would "echo" handle it as a string but the math fail to convert it? Example: $xml='<?xml version="1.0" encoding="UTF-8" ?>'; $xml.='<Test> <Item> <Price>0.53</Price> </Item> </Test>'; $result=simplexml_load_string($xml); var_dump($result->Item->Price); echo '<br>'; echo $result->Item->Price; echo '<br>'; echo 1+$result->Item->Price; echo '<br>'; echo 1+(float)$result->Item->Price; Output: object(SimpleXMLElement)#4 (1) { [0]=> string(4) "0.53" } 0.53 1 1.53

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  • Dynamically vs Statically typed languages studies

    - by Winston Ewert
    Do there exist studies done on the effectiveness of statically vs dynamically typed languages? In particular: Measurements of programmer productivity Defect Rate Also including the effects of whether or not unit testing is employed. I've seen lots of discussion of the merits of either side but I'm wondering whether anyone has done a study on it. Edit Sadly, only one of the papers shown is actually a study and it does nothing but conclude that the language matters. This leads me to ponder: what if I proposed doing such a study with volunteers from this site?

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  • How to change mimetype image for PSD file (Photoshop)?

    - by ubuntico
    Following this link https://help.ubuntu.com/community/AddingMimeTypes, I first typed a command to discover the mimetype for psd extension ~$ grep 'psd' /etc/mime.types image/x-photoshop psd Then I took Photoshop CS5 SVG image from Wikipedia and renamed it to image-x-photoshop.svg. Then I copied the file to the folder /usr/share/icons/gnome/scalable via command sudo cp image-x-photoshop.svg /usr/share/icons/gnome/scalable/image-x-photoshop.svg Loogged out, logged in, but the icon for the .psd files is still unchanged. Does anyone know what I am doing wrong? I use Ubuntu 10.10. Thanks in advance

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  • When should one use "out" parameters?

    - by qegal
    In Objective-C, there are several methods like initWithContentsOfFile:encoding:error: where one passes in a reference to an NSError object for the error: parameter. In this example, the value of the NSError object passed in can change based on what goes on at runtime when the method is being called and whether the body of the method was executed in a certain way successfully. In a way I think of this NSError object as sort of like a second return value from the method, and only differs from an object anObject in the statement return anObject; in that when this statement is called, execution leaves the method. So my question is, not only in the context of error handling in Objective-C, but in general, when should one use an "out" parameter in place of returning said value in a return statement?

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  • returning a heap block by reference in c++

    - by basicR
    I was trying to brush up my c++ skills. I got 2 functions: concat_HeapVal() returns the output heap variable by value concat_HeapRef() returns the output heap variable by reference When main() runs it will be on stack,s1 and s2 will be on stack, I pass the value by ref only and in each of the below functions, I create a variable on heap and concat them. When concat_HeapVal() is called it returns me the correct output. When concat_HeapRef() is called it returns me some memory address (wrong output). Why? I use new operator in both the functions. Hence it allocates on heap. So when I return by reference, heap will still be VALID even when my main() stack memory goes out of scope. So it's left to OS to cleanup the memory. Right? string& concat_HeapRef(const string& s1, const string& s2) { string *temp = new string(); temp->append(s1); temp->append(s2); return *temp; } string* concat_HeapVal(const string& s1, const string& s2) { string *temp = new string(); temp->append(s1); temp->append(s2); return temp; } int main() { string s1,s2; string heapOPRef; string *heapOPVal; cout<<"String Conact Experimentations\n"; cout<<"Enter s-1 : "; cin>>s1; cout<<"Enter s-2 : "; cin>>s2; heapOPRef = concat_HeapRef(s1,s2); heapOPVal = concat_HeapVal(s1,s2); cout<<heapOPRef<<" "<<heapOPVal<<" "<<endl; return -9; }

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  • Interface (contract), Generics (universality), and extension methods (ease of use). Is it a right design?

    - by Saeed Neamati
    I'm trying to design a simple conversion framework based on these requirements: All developers should follow a predefined set of rules to convert from the source entity to the target entity Some overall policies should be able to be applied in a central place, without interference with developers' code Both the creation of converters and usage of converter classes should be easy To solve these problems in C# language, A thought came to my mind. I'm writing it here, though it doesn't compile at all. But let's assume that C# compiles this code: I'll create a generic interface called IConverter public interface IConverter<TSource, TTarget> where TSource : class, new() where TTarget : class, new() { TTarget Convert(TSource source); List<TTarget> Convert(List<TSource> sourceItems); } Developers would implement this interface to create converters. For example: public class PhoneToCommunicationChannelConverter : IConverter<Phone, CommunicationChannle> { public CommunicationChannel Convert(Phone phone) { // conversion logic } public List<CommunicationChannel> Convert(List<Phone> phones) { // conversion logic } } And to make the usage of this conversion class easier, imagine that we add static and this keywords to methods to turn them into Extension Methods, and use them this way: List<Phone> phones = GetPhones(); List<CommunicationChannel> channels = phones.Convert(); However, this doesn't even compile. With those requirements, I can think of some other designs, but they each lack an aspect. Either the implementation would become more difficult or chaotic and out of control, or the usage would become truly hard. Is this design right at all? What alternatives I might have to achieve those requirements?

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  • Where is "open with..." in Nautilus?

    - by perebal
    In Ubuntu 11.04 I usually edit my *.fig files by clicking on the icons. The application (script) which opened the file was texfig. This script was chosen by "open with..." in nautilus. But now there is no possibilities to choose other applications than the predefined ones appropriate to the mimetype. How can I define a default application (or a self made script) in nautilus for the x-xfig mimetype?

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  • How to create a generic list in this wierd case in c#

    - by Marc Bettex
    Hello, In my program, I have a class A which is extended by B, C and many more classes. I have a method GetInstance() which returns a instance of B or C (or of one of the other child), but I don't know which one, so the return type of the method is A. In the method CreateGenericList(), I have a variable v of type A, which is in fact either a B, a C or another child type and I want to create a generic list of the proper type, i.e. List<B> if v is a B or List<C> if v is a C, ... Currently I do it by using reflection, which works, but this is extremely slow. I wanted to know if there is another way to to it, which doesn't use reflection. Here is an example of the code of my problem: class A { } class B : A { } class C : A { } // More childs of A. class Program { static A GetInstance() { // returns an instance of B or C } static void CreateGenericList() { A v = Program.GetInstance(); IList genericList = // Here I want an instance of List<B> or List<C> or ... depending of the real type of v, not a List<A>. } } I tried the following hack. I call the following method, hoping the type inferencer will guess the type of model, but it doesn't work and return a List<A>. I believe that because c# is statically typed, T is resolved as A and not as the real type of model at runtime. static List<T> CreateGenericListFromModel<T>(T model) where T : A { return new List<T> (); } Does anybody have a solution to that problem that doesn't use reflection or that it is impossible to solve that problem without reflection? Thank you very much, Marc

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  • Smart way to find the corresponding nullable type?

    - by Marc Wittke
    How could I avoid this dictionary (or create it dynamically)? Dictionary<Type,Type> CorrespondingNullableType = new Dictionary<Type, Type> { {typeof(bool), typeof(bool?)}, {typeof(byte), typeof(byte?)}, {typeof(sbyte), typeof(sbyte?)}, {typeof(char), typeof(char?)}, {typeof(decimal), typeof(decimal?)}, {typeof(double), typeof(double?)}, {typeof(float), typeof(float?)}, {typeof(int), typeof(int?)}, {typeof(uint), typeof(uint?)}, {typeof(long), typeof(long?)}, {typeof(ulong), typeof(ulong?)}, {typeof(short), typeof(short?)}, {typeof(ushort), typeof(ushort?)}, {typeof(Guid), typeof(Guid?)}, };

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  • Getting the name of a Clojure struct type?

    - by j-g-faustus
    When defining a struct type and instance, I can print the value and get the "struct" implementation type: (defstruct person :name :age) (def p (struct person "peter" 30)) user=> p {:name "peter", :age 30} user=> (type p) clojure.lang.PersistentStructMap But is it possible to tell whether p is an instance of the struct type "person"?

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  • Finding out document template type of document library

    - by blade
    Hi, When I make a document library in Sharepoint 2003 and select the document template type etc and come back to edit/administer the document library, how can I find out what document template type I selected at the time of creation? Another way of putting it: If an administrator makes a document library and selects a document template type and he/she leaves without documenting his/her settings for the document library, how could I find out what document template type he selected? Thanks

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  • Expecting a LexBuffer<char> but given a LexBuffer<byte> The type 'char' does not match the type 'by

    - by user152518
    Type mismatch. Expecting a LexBuffer but given a LexBuffer The type 'char' does not match the type 'byte' This is the error message that I am getting while using fslex. I have tried manually checking every single occurrence of lexbuf and its type. It's LexBuffer everywhere. But still the compiler is giving me the above error. Can you please tell me why this error occurs and how to go about resolving it. Thanks, chandrasekhar

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  • Type problem with Observable.Create from Boo

    - by Tristan
    I'm trying to use Reactive Extensions from Boo and am running into type problems. Here's the basic example: def OnSubscribe(observer as IObservable[of string]) as callable: print "subscribing" def Dispose(): print "disposing" return Dispose observable = System.Linq.Observable.Create[of string](OnSubscribe) observer = System.Linq.Observer.Create[of string]({x as string | print x}) observable.Subscribe(observer) The Subscribe here gives a System.InvalidCastException: Cannot cast from source type to destination type. The issue appears to be with how I'm creating the observable, but I've struggled to see where the type problem arises from. Ideas?

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