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  • Reference to an instance method of a particular object

    - by Andrey
    In the following code, if i try to pass method reference using the class name, works. But passing the reference variable compiler gives an error, i do not understand why? public class User { private String name; public User(String name) { this.name = name; } public void printName() { System.out.println(name); } } public class Main { public static void main(String[] args) { User u1 = new User("AAA"); User u2 = new User("BBB"); User u3 = new User("ZZZ"); List<User> userList = Arrays.asList(u1, u2, u3); userList.forEach(User::printName); // works userList.forEach(u1::printName); // compile error } } Thanks,

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  • How do you keep Cocoa controllers from getting too big?

    - by zoul
    Hello! Do you have some tricks or techniques to break Cocoa controller classes into smaller chunks? I find that whatever I do the controllers end up being one of the more complicated classes in my design. The basic stuff is simple, but once I have several pop-overs or action sheets running, things get uncomfortably complex. It's not that bad, but still I would like to refactor the code into several standalone chunks. I thought about categories, but the code is not that independent (a lot of times it needs to tap into viewWillAppear, for example) and I find that I spend a long time fighting the compiler. I also thought about adding functionality in layers using inheritance, but that feels like a hack.

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  • How do XAML files associate with cs files?

    - by LLS
    It seems that XAML files should have corresponding .cs files in a C# project. I know Visual Studio does all the things for us. I'm just curious how they are linked together? I mean, are they specified in the project file, or just because they have the same names? And also, App.xaml file specifies the startup file, but how does the compiler know? Is it possible to appoint another file other than App.xaml to do the same things as App.xaml does?

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  • Rails how to return a list of answers with a specific question_id

    - by mytwocentsisworthtwocents
    Let's say I have two Models, Answers and Questions (there are others, but irrelevant to the question). The models are as follows: Answer.rb class Answer < ActiveRecord::Base attr_accessible :description, :question_id has_one :question, :through => :user, :dependent => :destroy validates :description, :presence => true end Question.rb class Question < ActiveRecord::Base attr_accessible :budget, :description, :headline, :user_id, :updated_at, :created_at belongs_to :user has_many :answers validates :headline, :description, :user_id, :presence => true end I'd like to display on a page a list of all answers associated with a question, and only those questions. I got this far. I believe this variable finds all the questions in the database by the question_id (foreign key): @findanswers = Answer.all(params[:question_id]) And this one grabs the the id of the current question (this code will reside as an ERB on the page where the current question is located): @questionshow = Question.find(params[:id]) And now I'm stuck. How do I put the two together so that I list all the answers with the current question id?

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  • typedef fixed length array

    - by Rajorshi
    Hi, I have to define a 24-bit data type.I am using char[3] to represent the type. Can I typedef char[3] to type24? I tried it in a code sample. I put typedef char[3] type42; in my header file. The compiler did not complain about it. But when I defined a function void foo(type24 val) {} in my C file, it did complain. I would like to be able to define functions like type24_to_int32(type24 val) instead of type24_to_int32(char value[3]).

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  • Why Java cannot find my constructor?

    - by Roman
    Well, maybe it is a stupid question, but I cannot resolve this problem. In my ServiceBrowser class I have this line: ServiceResolver serviceResolver = new ServiceResolver(ifIndex, serviceName, regType, domain); And compiler complains about it. It says: cannot find symbol symbol : constructor ServiceResolver(int,java.lang.String,java.lang.String,java.lang.String) This is strange, because I do have a constructor in the ServiceResolver: public void ServiceResolver(int ifIndex, String serviceName, String regType, String domain) { this.ifIndex = ifIndex; this.serviceName = serviceName; this.regType = regType; this.domain = domain; } ADDED: I removed void from the constructor and it works! Why?

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  • How to call C++ function from C?

    - by claws
    I know this. Calling C function from C++: If my application was in C++ and I had to call functions from a library written in C. Then I would have used //main.cpp extern "C" void C_library_function(int x, int y);//prototype C_library_function(2,4);// directly using it. This wouldn't mangle the name C_library_function and linker would find the same name in its input *.lib files and problem is solved. Calling C++ function from C??? But here I'm extending a large application which is written in C and I need to use a library which is written in C++. Name mangling of C++ is causing trouble here. Linker is complaining about the unresolved symbols. Well I cannot use C++ compiler over my C project because thats breaking lot of other stuff. What is the way out? By the way I'm using MSVC

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  • Why does C++ linking use virtually no CPU? (updated)

    - by John
    On a native C++ project, linking right now can take a minute or two, yet during this time CPU drops from 100% during compilation to virtually zero. Does this mean linking is primarily a disk activity? If so, is this the main area an SSD would make big changes? But, why aren't all my OBJ files (or as many as possible) kept in RAM after compilation to avoid this? With 4Gb of RAM I should be able to save a lot of disk access and make it CPU-bound again, no? update: so the obvious follow-up is, can VC++ compiler and linker talk together better to streamline things and keep OBJ files in memory, similar to how Delphi does?

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  • Writing a jquery plugin in coffeescript - how to get "(function($)" and "(jQuery)"?

    - by PandaWood
    I am writing a jquery plugin in coffeescript but am not sure how to get the function wrapper part right. My coffeescript starts with this line: $.fn.extend({ Which creates the javascript with a function wrapper: (function() { $.fn.extend({ but I want a '$' passed in like this: (function($) { $.fn.extend({ Similar for the ending I have... nothing in particular in coffeescript. I get this in javascript: })(); But would like this: })(jQuery); Does anyone know how to achieve this with the coffeescript compiler? Or what is the best way to get this done within coffeescript?

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  • Why is there "data" and "newtype" in Haskell?

    - by martingw
    To me it seems that a newtype definition is just a data definition that obeys some restrictions (only one constructor and such), and that due to these restrictions the runtime system can handle newtypes more efficiently. Ok, and the handling of pattern matching for undefined values is slightly different. But suppose Haskell would only knew data definitions, no newtypes: Couldn't the compiler find out for himself whether a given data definition obeys these restrictions, and automatically treat it more efficiently? I'm sure I'm missing out on something, these Haskell designers are so clever, there must be some deeper reason for this...

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  • creating tables in ruby-on-rails 3 through migrations?

    - by fayer
    im trying to understand the process of creating tables in ruby-on-rails 3. i have read about migrations. so i am supposed to create tables by editing in the files in: Database Migrations/migrate/20100611214419_create_posts Database Migrations/migrate/20100611214419_create_categories but they were generated by: rails generate model Post name:string description:text rails generate model Category name:string description:text does this mean i have to use "rails generate model" command everytime i want to create a table? what if i create a migration file but want to add columns. do i create another migration file for adding those or do i edit the existing migration file directly? the guide told me to add a new one, but here is the part i dont understand. why would i add a new one? cause then the new state will be dependent of 2 migration files. in symfony i just edit a schema.yml file directly, there are no migration files with versioning and so on. im new to RoR and want to get the picture of creating tables. thanks

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  • How to understand the programming of an operating system

    - by piemesons
    Hello, I want to learn the operating system. How it works. I don't want to make my own operating system. I just want to learn how it works. As I can find out source code of any open source OS. But how to start. Like starting from the first elementary kernel (whatever it is). Somebody suggested I try to implement Linux from scratch etc. Please guide me in a proper way. I want to know about the proper path to follow. I am ready to invest three to four years just to understand the basics. I have good fundamentals of C, C++, PHP, OOP and compiler design.

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  • can't create partial objects with accepts_nested_attributes_for

    - by Isaac Cambron
    I'm trying to build a form that allows users to update some records. They can't update every field, though, so I'm going to do some explicit processing (in the controller for now) to update the model vis-a-vis the form. Here's how I'm trying to do it: Family model: class Family < ActiveRecord::Base has_many :people, dependent: :destroy accepts_nested_attributes_for :people, allow_destroy: true, reject_if: ->(p){p[:name].blank?} end In the controller def check edited_family = Family.new(params[:family]) #compare to the one we have in the db #update each person as needed/allowed #save it end Form: = form_for current_family, url: check_rsvp_path, method: :post do |f| = f.fields_for :people do |person_fields| - if person_fields.object.user_editable = person_fields.text_field :name, class: "person-label" - else %p.person-label= person_fields.object.name The problem is, I guess, that Family.new(params[:family]) tries to pull the people out of the database, and I get this: ActiveRecord::RecordNotFound in RsvpsController#check Couldn't find Person with ID=7 for Family with ID= That's, I guess, because I'm not adding a field for family id to the nested form, which I suppose I could do, but I don't actually need it to load anything from the database for this anyway, so I'd rather not. I could also hack around this by just digging through the params hash myself for the data I need, but that doesn't feel a slick. It seems nicest to just create an object out of the params hash and then work with it. Is there a better way? How can I just create the nested object?

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  • Ruby on rails 2 level model

    - by jony17
    I need some help creating a very simple forum in a existing model. What I want in a Game page, have a mini forum, where is possible create some topics and some comments to this topics. In the beginning I'm only implement topics. This is the error I have: Mysql2::Error: Column 'user_id' cannot be null: INSERT INTO `topics` (`game_id`, `question`, `user_id`) VALUES (1, 'asd', NULL) This is my main model: game.rb class Game < ActiveRecord::Base attr_accessible :name validates :user_id, presence: true validates :name, presence: true, length: { maximum: 50 } belongs_to :user has_many :topics, dependent: :destroy end topic.rb class Topic < ActiveRecord::Base validates_presence_of :question validates_presence_of :game_id attr_accessible :question, :user_id validates :question, length: {maximum: 50}, allow_blank: false belongs_to :game belongs_to :user end topic_controller.rb def create @game = Game.find(params[:game_id]) @topic = @game.topics.create(params[:topic]) @topic.user_id = current_user.id respond_to do |format| if @topic.save format.html { redirect_to @game, notice: 'Topic was successfully created.' } else format.html { render action: "new" } end end end game/show.html.erb <h2>Topics</h2> <% @game.topics.each do |topic| %> <p> <b>Question:</b> <%= topic.question %> </p> <% end %> <h2>Add a topic:</h2> <%= form_for([@game, @game.topics.build]) do |f| %> <div class="field"> <%= f.label :question %><br /> <%= f.text_field :question %> </div> <div class="actions"> <%= f.submit %> </div> <% end %> Thanks ;)

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  • how to databind a datalist's page index to a button's commandname?

    - by korben
    i got this inside a button inside a datalist CommandName="<%# Container.ItemIndex %>" when i click the button, i'm expecting commandname to = 0, then 1, then 2, etc, as the datalist progresses, and i'm using that value in the button click's c# but i'm getting this error, i'm pretty sure i'm using this exact setup on another page and i have no problems, any idea what's going on? Server Error in '/' Application. Compilation Error Description: An error occurred during the compilation of a resource required to service this request. Please review the following specific error details and modify your source code appropriately. Compiler Error Message: CS0117: 'System.Web.UI.Control' does not contain a definition for 'ItemIndex'

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  • How can I compare the performance of log() and fp division in C++?

    - by Ventzi Zhechev
    Hi, I’m using a log-based class in C++ to store very small floating-point values (as the values otherwise go beyond the scope of double). As I’m performing a large number of multiplications, this has the added benefit of converting the multiplications to sums. However, at a certain point in my algorithm, I need to divide a standard double value by an integer value and than do a *= to a log-based value. I have overloaded the *= operator for my log-based class and the right-hand side value is first converted to a log-based value by running log() and than added to the left-hand side value. Thus the operations actually performed are floating-point division, log() and floating-point summation. My question whether it would be faster to first convert the denominator to a log-based value, which would replace the floating-point division with floating-point subtraction, yielding the following chain of operations: twice log(), floating-point subtraction, floating-point summation. In the end, this boils down to whether floating-point division is faster or slower than log(). I suspect that a common answer would be that this is compiler and architecture dependent, so I’ll say that I use gcc 4.2 from Apple on darwin 10.3.0. Still, I hope to get an answer with a general remark on the speed of these two operators and/or an idea on how to measure the difference myself, as there might be more going on here, e.g. executing the constructors that do the type conversion etc. Cheers!

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  • Trouble using files Globally

    - by Nightforce2
    Recently I ran into trouble when I discovered that vista restricts what can be installed into the system32 directory even though I am the administrator for this computer. It will not allow me to register dll files so I can use programs like wget globally like how programs "nslookup" etc are used. Keeps giving me this error. Regsvr32: The module "C:\Windows\System32\libeay32.dll" failed to load. make sure the binary is stored at the specified path or debug it to check for problems with the binary or dependent .DLL files. The specified module could not be found. Moving the required DLL files to system32 prompts me to confirm administrator privileges are needed to move these files, So I give the permission, copy the files to system32, and run wget to confirm. This is where it tells me it cannot find the DLL's required to run and when using regsvr32 it says it cannot find the entry point so it will not load the DLL asking me if it is a valid DLL or OCX file. If I leave the DLL's that came with wget in the same folder as wget outsite of system32 they work vice adding them to system32 with the exe it will not work saying it cannot read the those dll files. Is there a way around this or Do I need to Upgrade to Windows 7 to get away from these problems/restrictions?

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  • Android application displays black screen after running

    - by frgnvola
    When I click "Run as an Android Application" on Eclipse, the following is displayed in the console [2014-06-05 20:07:18 - StudentConnect] Android Launch! [2014-06-05 20:07:18 - StudentConnect] adb is running normally. [2014-06-05 20:07:18 - StudentConnect] Performing sandhu.student.connect.SplashActivity activity launch [2014-06-05 20:07:18 - StudentConnect] Using default Build Tools revision 19.0.0 [2014-06-05 20:07:18 - StudentConnect] Refreshing resource folders. [2014-06-05 20:07:18 - StudentConnect] Using default Build Tools revision 19.0.0 [2014-06-05 20:07:18 - StudentConnect] Starting incremental Pre Compiler: Checking resource changes. [2014-06-05 20:07:18 - StudentConnect] Nothing to pre compile! [2014-06-05 20:07:18 - StudentConnect] Starting incremental Package build: Checking resource changes. [2014-06-05 20:07:18 - StudentConnect] Using default Build Tools revision 19.0.0 [2014-06-05 20:07:18 - StudentConnect] Skipping over Post Compiler. [2014-06-05 20:07:20 - StudentConnect] Application already deployed. No need to reinstall. [2014-06-05 20:07:20 - StudentConnect] Starting activity sandhu.student.connect.SplashActivity on device 0f0898b2 [2014-06-05 20:07:21 - StudentConnect] ActivityManager: Starting: Intent { act=android.intent.action.MAIN cat=[android.intent.category.LAUNCHER] cmp=sandhu.student.connect/.SplashActivity } [2014-06-05 20:07:21 - StudentConnect] ActivityManager: Warning: Activity not started, its current task has been brought to the front After deployed to my phone, it only displays a black screen. I recently implemented a splash screen, but it was working fine before; however I think it might have something to do with the problem. Here are my java and xml files: MainActivity.java package sandhu.student.connect; import android.app.Activity; import android.os.Bundle; import android.view.KeyEvent; import android.view.View; import android.webkit.WebSettings; import android.webkit.WebView; import android.webkit.WebViewClient; public class MainActivity extends Activity { public WebView student_zangle; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); WebView student_zangle = (WebView) findViewById(R.id.student_zangle); student_zangle.loadUrl("https://zangleweb01.clovisusd.k12.ca.us/studentconnect/"); student_zangle.setWebViewClient(new WebViewClient()); student_zangle.setScrollBarStyle(View.SCROLLBARS_INSIDE_OVERLAY); WebSettings settings = student_zangle.getSettings(); settings.setJavaScriptEnabled(true); settings.setBuiltInZoomControls(true); settings.setLoadWithOverviewMode(true); settings.setUseWideViewPort(true); } @Override public boolean onKeyDown(int keyCode, KeyEvent event) { WebView student_zangle = (WebView) findViewById(R.id.student_zangle); if ((keyCode == KeyEvent.KEYCODE_BACK) && student_zangle.canGoBack()) { student_zangle.goBack(); return true; } else { finish(); } return super.onKeyDown(keyCode, event); } } activity_main.xml <?xml version="1.0" encoding="utf-8"?> <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent" android:layout_height="match_parent" android:background="@drawable/blue" tools:context=".MainActivity" > <WebView android:id="@+id/student_zangle" android:layout_width="match_parent" android:layout_height="match_parent" /> </RelativeLayout> SplashActivity.java package sandhu.student.connect; import android.os.Bundle; import android.preference.PreferenceActivity; public class SplashActivity extends PreferenceActivity { @SuppressWarnings("deprecation") @Override protected void onCreate(Bundle savedInstanceState) { // TODO Auto-generated method stub super.onCreate(savedInstanceState); addPreferencesFromResource(R.xml.prefs); } } splash_activity.xml <?xml version="1.0" encoding="utf-8"?> <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="match_parent" android:layout_height="match_parent" android:background="@drawable/blue" android:orientation="vertical" > <ImageView android:id="@+id/imageView1" android:layout_width="250dp" android:layout_height="100dp" android:layout_alignParentTop="true" android:layout_centerHorizontal="true" android:layout_marginTop="145dp" android:contentDescription="@string/zangle_logo" android:src="@drawable/logo" /> </RelativeLayout> Also, here is a full copy of the logcat error output: 06-05 20:19:46.698: E/Watchdog(817): !@Sync 1952 06-05 20:20:09.971: E/memtrack(16438): Couldn't load memtrack module (No such file or directory) 06-05 20:20:09.971: E/android.os.Debug(16438): failed to load memtrack module: -2 06-05 20:20:11.012: E/memtrack(16451): Couldn't load memtrack module (No such file or directory) 06-05 20:20:11.012: E/android.os.Debug(16451): failed to load memtrack module: -2 06-05 20:20:11.202: E/EnterpriseContainerManager(817): ContainerPolicy Service is not yet ready!!! Please help me figure out what is wrong, or at least point me in the right direction. Thanks in advance.

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  • Are C++ Templates just Macros in disguise?

    - by Roddy
    I've been programming in C++ for a few years, and I've used STL quite a bit and have created my own template classes a few times to see how it's done. Now I'm trying to integrate templates deeper into my OO design, and a nagging thought keeps coming back to me: They're just a macros, really... You could implement (rather UGLY) auto_ptrs using #defines, if you really wanted to. This way of thinking about templates helps me understand how my code will actually work, but I feel that I must be missing the point somehow. Macros are meant evil incarnate, yet "template metaprogramming" is all the rage. So, what ARE the real distinctions? and how can templates avoid the dangers that #define leads you into, like Inscrutable compiler errors in places where you don't expect them? Code bloat? Difficulty in tracing code? Setting Debugger Breakpoints?

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  • How would one call std::forward on all arguments in a variadic function?

    - by Noah Roberts
    I was just writing a generic object factory and using the boost preprocessor meta-library to make a variadic template (using 2010 and it doesn't support them). My function uses rval references and std::forward to do perfect forwarding and it got me thinking...when C++0X comes out and I had a standard compiler I would do this with real variadic templates. How though, would I call std::forward on the arguments? template < typename ... Params void f(Params ... params) // how do I say these are rvalue reference? { y(std::forward(...params)); //? - I doubt this would work. } Only way I can think of would require manual unpacking of ...params and I'm not quite there yet either. Is there a quicker syntax that would work?

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  • Visual Studio 2010 Compiling C code

    - by Corsen2000
    I have the following code snippet. This is a c file in visual studio 2010. If i try to compile this with the line: int hello = 10; commented out it will compile just fine. If I comment that line in it will not compile. Am I missing something or should I not be using Visual Studio 2010 to compile C code. If this is a Visual Studio problem can anyone recommend a easy to use IDE / Compiler that I can for C. Thank You int* x = (int*) calloc(1, sizeof(int)); *x = 5; //int hello = 10; printf("Hello World! %i", *x); getchar();

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  • Fast comparison of char arrays?

    - by StackedCrooked
    I'm currently working in a codebase where IPv4 addresses are represented as pointers to u_int8. The equality operator is implemented like this: bool Ipv4Address::operator==(const u_int8 * inAddress) const { return (*(u_int32*) this->myBytes == *(u_int32*) inAddress); } This is probably the fasted solution, but it causes the GCC compiler warning: ipv4address.cpp:65: warning: dereferencing type-punned pointer will break strict-aliasing rules How can I rewrite the comparison correctly without breaking strict-aliasing rules and without losing performance points? I have considered using either memcmp or this macro: #define IS_EQUAL(a, b) \ (a[0] == b[0] && a[1] == b[1] && a[2] == b[2] && a[3] == b[3]) I'm thinking that the macro is the fastest solution. What do you recommend?

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  • Can I add a custom method to Core Data-generated classes?

    - by Andy
    I've got a couple of Core Data-generated class files that I'd like to add custom methods to. I don't need to add any instance variables. How can I do this? I tried adding a category of methods: // ContactMethods.h (my category on Core Data-generated "Contact" class) #import "Contact.h" @interface Contact (ContactMethods) -(NSString*)displayName; @end ... // ContactMethods.m #import "ContactMethods.h" @implementation Contact (ContactMethods) -(NSString*)displayName { return @"Some Name"; // this is test code } @end This doesn't work, though. I get a compiler message that "-NSManagedObject may not respond to 'displayName' " and sure enough, when I run the app, I don't get "Some Name" where I should be seeing it.

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  • how to access child instances in a vector in c++

    - by tsubasa
    I have a parent class and child class (inherited from parent). In the child class, I have a member function named function_blah(); I used vector<parent*> A to store 5 parent instances, 3 child instances. So the total number of elements in the vector is 8. I can easily access to member functions of element A[0] to A[4], which are parent instances. But whenever I try to have access to member functions of element A[5] to A[7], the compiler complains that class parent has no member named 'function_blah' The way I access to elements is using index. e.x A[i] with i = 0..7. Is it correct? if not, how?

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  • boost variant static_visitor problem picking correct function

    - by Steve
    I'm sure I'm having a problem with template resolution here, but I'm not sure why I'm having the problem. I have a static visitor I'm passing to boost variant where i've had to do template specialization for certain cases. The case for everything except for MyClass should throw in the static_visitor below. Unfortunately, when the visitor is applied to pull a MyClass out, it selects the most generic case rather than the exact match. I would type each case explicitly, but that will be rather long. So, why is the compiler resolving the most generic case over the exact match, and is there anyway to fix it template<> class CastVisitor<MyClass>:public boost::static_visitor<MyClass> { public: template<typename U> MyClass operator()(const U & i) const { throw std::exception("Unable to cast"); } MyClass operator()(const MyClass& i) { return i; } };

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