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How to use derived class shared variables in shared methods of base class

- by KoolKabin

Hi guys, I am trying to add shared members in derived classes and use that values in base classes... I have base class DBLayer public shared function GetDetail(byval UIN as integer) dim StrSql = string.format("select * from {0} where uin = {1}", tablename, uin) .... end function end class my derived class class User inherits dblayer public shared tabledname as string = "users" end class class item inherits dblayer public shared tabledname as string = "item" end class class category inherits dblayer public shared tabledname as string = "category" end class currently there is error using the tablename variable of derived class in base class but i want to use it... coz i dun know other techniques... if other solutions are better then u can post it or u can say how can i make it work? confused...

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Advantages of Singleton Class over Static Class?

Point 1)Singleton We can get the object of singleton and then pass to other methods.Static Class We can not pass static class to other methods as we pass objectsPoint 2) Singleton In future, it is easy to change the logic of of creating objects to some pooling mechanism. Static Class Very difficult to implement some pooling logic in case of static class. We would need to make that class as non-static and then make all the methods non-static methods, So entire your code needs to be changed.Point3:) Singleton Can Singletone class be inherited to subclass? Singleton class does not say any restriction of Inheritence. So we should be able to do this as long as subclass is also inheritence.There's nothing fundamentally wrong with subclassing a class that is intended to be a singleton. There are many reasons you might want to do it. and there are many ways to accomplish it. It depends on language you use.Static Class We can not inherit Static class to another Static class in C#. Think about it this way: you access static members via type name, like this: MyStaticType.MyStaticMember(); Were you to inherit from that class, you would have to access it via the new type name: MyNewType.MyStaticMember(); Thus, the new item bears no relationships to the original when used in code. There would be no way to take advantage of any inheritance relationship for things like polymorphism. span.fullpost {display:none;}

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Advantages of Singleton Class over Static Class?

Point 1) Singleton We can get the object of singleton and then pass to other methods. Static Class We can not pass static class to other methods as we pass objects Point 2) Singleton In future, it is easy to change the logic of of creating objects to some pooling mechanism. Static Class Very difficult to implement some pooling logic in case of static class. We would need to make that class as non-static and then make all the methods non-static methods, So entire your code needs to be changed. Point3:) Singleton Can Singletone class be inherited to subclass? Singleton class does not say any restriction of Inheritence. So we should be able to do this as long as subclass is also inheritence.There's nothing fundamentally wrong with subclassing a class that is intended to be a singleton. There are many reasons you might want to do it. and there are many ways to accomplish it. It depends on language you use. Static Class We can not inherit Static class to another Static class in C#. Think about it this way: you access static members via type name, like this: MyStaticType.MyStaticMember(); Were you to inherit from that class, you would have to access it via the new type name: MyNewType.MyStaticMember(); Thus, the new item bears no relationships to the original when used in code. There would be no way to take advantage of any inheritance relationship for things like polymorphism. span.fullpost {display:none;}

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Manager/Container class vs static class methods

- by Ben

Suppose I a have a Widget class that is part of a framework used independently by many applications. I create Widget instances in many situations and their lifetimes vary. In addition to Widget's instance specified methods, I would like to be able to perform the follow class wide operations: Find a single Widget instance based on a unique id Iterate over the list of all Widgets Remove a widget from the set of all widgets In order support these operations, I have been considering two approaches: Container class - Create some container or manager class, WidgetContainer, which holds a list of all Widget instances, support iteration and provides methods for Widget addition, removal and lookup. For example in C#: public class WidgetContainer : IEnumerable<Widget { public void AddWidget(Widget); public Widget GetWidget(WidgetId id); public void RemoveWidget(WidgetId id); } Static class methods - Add static class methods to Widget. For example: public class Widget { public Widget(WidgetId id); public static Widget GetWidget(WidgetId id); public static void RemoveWidget(WidgetId id); public static IEnumerable<Widget AllWidgets(); } Using a container class has the added problem of how to access the container class. Make it a singleton?..yuck! Create some World object that provides access to all such container classes? I have seen many frameworks that use the container class approach, so what is the general consensus?

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class inheretence of a attribute which is itself a class

- by alex

i have a class which inherets a attribute from a super-class. this attribute is a class itself. class classA(superClass): def func(self,x): if self.attributeB is None: do somthing and in the other class i have class superClass: self.attributB = classB() i get the error AttributeError: class classA has no attribute 'attributeB' when i access the attribute like i showed but if on command line i can see it works, x = classA() x.attributeB is None True so the test works. whats going on in the above code?

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Using a database class in my user class

- by Josh

In my project I have a database class that I use to handle all the MySQL stuff. It connects to a database, runs queries, catches errors and closes the connection. Now I need to create a members area on my site, and I was going to build a users class that would handle registration, logging in, password/username changes/resets and logging out. In this users class I need to use MySQL for obvious reasons... which is what my database class was made for. But I'm confused as to how I would use my database class in my users class. Would I want to create a new database object for my user class and then have it close whenever a method in that class is finished? Or do I somehow make a 'global' database class that can be used throughout my entire script (if this is the case I need help with that, no idea what to do there.) Thanks for any feedback you can give me.

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Using a datanase class in my user class?

- by Josh

In my project I have a database class that I use to handle all the MySQL stuff. It connects to a database, runs queries, catches errors and closes the connection. Now I need to create a members area on my site, and I was going to build a users class that would handle registration, logging in, password/username changes/resets and logging out. In this users class I need to use MySQL for obvious reasons... which is what my database class was made for. But I'm confused as to how I would use my database class in my users class. Would I want to create a new database object for my user class and then have it close whenever a method in that class is finished? Or do I somehow make a 'global' database class that can be used throughout my entire script (if this is the case I need help with that, no idea what to do there.) Thanks for any feedback you can give me.

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Can i access outer class objects in inner class

- by Shantanu Gupta

I have three classes like this. class A { public class innerB { //Do something } public class innerC { //trying to access objB here directly or indirectly over here. //I dont have to create an object of innerB, but to access the object created by A //i.e. innerB objInnerB = objB; //not like this innerB objInnerB= new innerB(); } public innerB objB{get;set;} } I want to access the object of class B in Class C that is created by class A. Is it possible somehow to make changes on object of Class A in Class C. Can i get Class A's object by creating event or anyhow.

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Linking a template class using another template class (error LNK2001)

- by Luís Guilherme

I implemented the "Strategy" design pattern using an Abstract template class, and two subclasses. Goes like this: template <class T> class Neighbourhood { public: virtual void alter(std::vector<T>& array, int i1, int i2) = 0; }; and template <class T> class Swap : public Neighbourhood<T> { public: virtual void alter(std::vector<T>& array, int i1, int i2); }; There's another subclass, just like this one, and alter is implemented in the cpp file. Ok, fine! Now I declare another method, in another class (including neighbourhood header file, of course), like this: void lSearch(/*parameters*/, Neighbourhood<LotSolutionInformation> nhood); It compiles fine and cleanly. When starting to link, I get the following error: 1>SolverFV.obj : error LNK2001: unresolved external symbol "public: virtual void __thiscall lsc::Neighbourhood<class LotSolutionInformation>::alter(class std::vector<class LotSolutionInformation,class std::allocator<class LotSolutionInformation> > &,int,int)" (?alter@?$Neighbourhood@VLotSolutionInformation@@@lsc@@UAEXAAV?$vector@VLotSolutionInformation@@V?$allocator@VLotSolutionInformation@@@std@@@std@@HH@Z)

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Building a database class in PHP

- by Sprottenwels

I wonder if I should write a database class for my application, and if so, how to accomplish it? Over there on SO, a guy mentioned it should be written as an abstract class. However, I can't understand why this would be a benefit. Do I understand correctly, that if I would write an abstract class, every other class that methods will need a database connection, could simply extend this abstract class and have it's own database object? If so, how is this different from a "normal" class where I could instantiate an database object? Another method would be to completely forget about my own class and to instantiate a mysqli object on demand. What do you recommend?

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Class design for calling "the same method" on different classes from one place

- by betatester07

Let me introduce my situation: I have Java EE application and in one package, I want to have classes which will act primarily as cache for some data from database, for example: class that will hold all articles for our website class that will hold all categories etc. Every class should have some update() method, which will update data for that class from database and also some other methods for data manipulation specific for that data type. Now, I would like to call update() method for all class instances (there will be exactly one class instance for every class) from one place. What is the best design?

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How to easily substitute a Base class

- by JTom

Hi, I have the following hierarchy of classes class classOne { virtual void abstractMethod() = 0; }; class classTwo : public classOne { }; class classThree : public classTwo { }; All classOne, classTwo and classThree are abstract classes, and I have another class that is defining the pure virtual methods class classNonAbstract : public classThree { void abstractMethod(); // Couple of new methods void doIt(); void doItToo(); }; And right now I need it differently...I need it like class classNonAbstractOne : public classOne { void abstractMethod(); // Couple of new methods void doIt(); void doItToo(); }; class classNonAbstractTwo : public classTwo { void abstractMethod(); // Couple of new methods void doIt(); void doItToo(); }; and class classNonAbstractThree : public classThree { void abstractMethod(); // Couple of new methods void doIt(); void doItToo(); }; But all the nonAbstract classes have the same new methods, with the same code...and I would like to avoid copying all the methods and it's code to every nonAbstract class. How could I accomplish that? Hopefully it's understandable...

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Using a class within a class?

- by Josh

I built myself a MySQL class which I use in all my projects. I'm about to start a project that is heavily based on user accounts and I plan on building my own class for this aswell. The thing is, a lot of the methods in the user class will be MySQL queries and methods from the MySQL class. For example, I have a method in my user class to update someone's password: class user() { function updatePassword($usrName, $newPass) { $con = mysql_connect('db_host', 'db_user', 'db_pass'); $sql = "UPDATE users SET password = '$newPass' WHERE username = '$userName'"; $res = mysql_query($sql, $con); if($res) return true; mysql_close($con); } } (I kind of rushed this so excuse any syntax errors :) ) As you can see that would use MySQL to update a users password, but without using my MySQL class, is this correct? I see no way in which I can use my MySQL class within my users class without it seeming dirty. Do I just use it the normal way like $DB = new DB();? That would mean including my mysql.class.php somewhere too... I'm quite confused about this, so any help would be appreciated, thanks.

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Identifying that a variable is a new-style class in Python?

- by Dave Johansen

I'm using Python 2.x and I'm wondering if there's a way to tell if a variable is a new-style class? I know that if it's an old-style class that I can do the following to find out. import types class oldclass: pass def test(): o = oldclass() if type(o) is types.InstanceType: print 'Is old-style' else: print 'Is NOT old-style' But I haven't been able to find anything that works for new-style classes. I found this question, but the proposed solutions don't seem to work as expected, because simple values as are identified as classes. import inspect def newclass(object): pass def test(): n = newclass() if inspect.isclass(n): print 'Is class' else: print 'Is NOT class' if inspect.isclass(type(n)): print 'Is class' else: print 'Is NOT class' if inspect.isclass(type(1)): print 'Is class' else: print 'Is NOT class' if isinstance(n, object): print 'Is class' else: print 'Is NOT class' if isinstance(1, object): print 'Is class' else: print 'Is NOT class' So is there anyway to do something like this? Or is everything in Python just a class and there's no way to get around that?

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How to get a Class literal from a generically specific Class

- by h2g2java

There are methods like these which require Class literals as argument. Collection<EmpInfo> emps = SomeSqlUtil.select( EmpInfo.class, "select * from emps"); or GWT.create(Razmataz.class); The problem presents itself when I need to supply generic specific classes like EmpInfo<String> Razmataz<Integer> The following would be wrong syntax Collection<EmpInfo<String>> emps = SomeSqlUtil.select( EmpInfo<String>.class, "select * from emps"); or GWT.create(Razmataz<Integer>.class); Because you cannot do syntax like Razmataz<Integer>.class So, how would I be able to squeeze a class literal out of EmpInfo<String> Razmataz<Integer> so that I could feed them as arguments to methods requiring Class literals? Further info Okay, I confess that I am asking this primarily for GWT. I have a pair of GWT RPC interface Razmataz. (FYI, GWT RPC interface has to be defined in server-client pairs). I plan to use the same interface pair for communicating whether it be String, Integer, Boolean, etc. GWT.create(Razmataz) for Razmataz<T> complains that, since I did not specify T, GWT compiler treated it as Object. Then GWT compiler would not accept Object class. It needs to be more specific than being an Object. So, it seems there is no way for me to tell GWT.create what T is because a Class literal is a runtime concept while generics is a compile time concept, Right?

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Getting the class of an n dimensional array of an runtime supplied class name

- by MeBigFatGuy

Given a fully qualified class name, and a number of dimensions, i would like to get the Class name for this class. I believe i can do this like such public Class<?> getArrayClass(String className, int dimensions) throws ClassNotFoundException { Class<?> elementType = Class.forName(className); return Array.newInstance(elementType, new int[dimensions]).getClass(); } However this requires me to create an unneeded instance of the class. Is there a way to do this without creating the instance? It does not appear that Class.forName("[[[[Ljava/lang/String;") (or a algorithmically generated version) works correctly in all instances from various blog posts i've seen.

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Returning and instance of a Class given its .class (MyClass.class)

- by jax

I have an enum that will hold my algorithms. I cannot instantiate these classes because I need the application context which is only available once the application has started. I want to load the class at runtime when I choose by calling getAlgorithm(Context cnx). How do I easily instantiate a class at runtime given its .class (and my constructor takes arguments)? All my classes are subclasses of Algorithm. public enum AlgorithmTypes { ALL_FROM_9_AND_LAST_FROM_10_ID(AlgorithmFactory.AlgorithmAllFrom9AndLastFrom10Impl.class), ALL_FROM_9_AND_LAST_FROM_10_CURRENCY_ID(AlgorithmFactory.AlgorithmAllFrom9AndLastFrom10Impl.class), DIVIDE_BY_9_LESS_THAN_100(AlgorithmFactory.AlgorithmAllFrom9AndLastFrom10Impl.class), TABLES_BEYOND_5_BY_5(AlgorithmFactory.AlgorithmAllFrom9AndLastFrom10Impl.class); private Class<? extends Algorithm> algorithm; AlgorithmTypes(Class<? extends Algorithm> c) { algorithm = c; } public Algorithm getAlgorithm(Context cnx) { return //needs to return the current algoriths constructor which takes the Context Algorithm(Context cnx); } }

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AS3 "Loader" progress immediately goes to 100%

- by Bart van Heukelom

If you go to http://moederdagontbijtplacemat.nl/ you will see a progress bar. The application is loading a fairly large SWF from the server using the Loader class. Strangely enough, the progress bar immediately goes to 100% (but the loading still takes a while after that). The code is below, but you'll see it's basically too simple to break. It has worked when the application was on a different server, so I though maybe the new server wasn't sending the size of the large SWF in the http headers. Firebug does show a progress bar though, so that is not the case, the information should be available. It also works when I run the loader swf locally and change the URL (new URLRequest("Placemat.swf")) to the absolute URL of Placemat.swf on the server. var l:Loader = new Loader(); addChild(l); l.contentLoaderInfo.addEventListener(ProgressEvent.PROGRESS, function(e:ProgressEvent) { s.setProgress(e.bytesLoaded/e.bytesTotal); trace(Math.round(100 * e.bytesLoaded/e.bytesTotal), "%"); }); l.contentLoaderInfo.addEventListener(Event.COMPLETE, function() { removeChild(s); }); l.load(new URLRequest("Placemat.swf"));

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Problem resizing loader after loading swf

- by DanK

I'm using the following code to load an swf in a pure actionscript project (Flex Builder 3) _loader = new Loader(); _loader.contentLoaderInfo.addEventListener(Event.COMPLETE, Loader_Complete); _loader.contentLoaderInfo.addEventListener(Event.INIT, Loader_Init); var request:URLRequest = new URLRequest("Skins/TestSkin.swf"); _loader.load(request); this.addChild(_loader); This works okay and displays the swf on the stage (500x375 for some reason - not sure why, TestSkin.swf is a flex app with no defined width and height) However, when I try to scale the swf so that it will fill the stage, I have problems. I have tried: Setting _loader.width and _loader.height in my Loader_Complete handler Setting _loader.width and _loader.height in my Loader_Init handler Setting _loader.content.width and loader.content.height in my Loader_Complete handler Setting _loader.content.width and loader.content.height in my Loader_Init handler I have seen examples online where people say these work for them but whenever I set width or height in any of these ways, the loaded swf is simply not displayed at all. Any idea what could be causing this? What is the correct way to resize an swf that has been loaded with a Loader object?

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How to add class to selective <li> in a generated menu

- by Vikram

Hi I am looking for a solution to add a class to every list item <li> which has a child item with a class of <span class="separator"> and a different class to <li> with an anchor link. I use Joomla and the menu is being generated somewhat like this: <ul class="menu"> <li class="item1"><a href=""><span>Home</span></a></li> <li class="parent item59"><span class="separator"><span>Demo</span></span></li> <li class="item62"><a href=""><span>Article</span></a></li> <li id="current" class="parent active item27"><a href=""><span>CMS</span></a> <ul> <li class="item50"><a href=""><span>The News</span></a></li> <li class="item48"><a href=""><span>Web Links</span></a></li> <li class="item65"><span class="separator"><span /></span></li> <li class="item49"><a href=""><span>News Feeds</span></a></li> <li class="item66"><span class="separator"><span /></span></li> <li class="item67"><span class="separator"><span /></span></li> <li class="item68"><span class="separator"><span /></span></li> </ul> </li> <li class="item71"><span class="separator"><span>Help</span></span></li> </ul> What I want is to add class "anclink" or "seplink" to the <li> depending on their child item so that the final output looks like below. <ul class="menu"> <li class="item1 anclink"><a href=""><span>Home</span></a></li> <li class="parent item59 seplink"><span class="separator"><span>Demo</span></span></li> <li class="item62 anclink"><a href=""><span>Article</span></a></li> <li id="current" class="parent active item27" anclink><a href=""><span>CMS</span></a> <ul> <li class="item50 anclink"><a href=""><span>The News</span></a></li> <li class="item48 anclink"><a href=""><span>Web Links</span></a></li> <li class="item65 seplink"><span class="separator"><span /></span></li> <li class="item49 anclink"><a href=""><span>News Feeds</span></a></li> <li class="item66 seplink"><span class="separator"><span /></span></li> <li class="item67 seplink"><span class="separator"><span /></span></li> <li class="item68 seplink"><span class="separator"><span /></span></li> </ul> </li> <li class="item71 seplink"><span class="separator"><span>Help</span></span></li> </ul> How can I achieve this using PHP or even a jQuery solution will be fine. Kindly help.

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Loader for images that are in another page that are gathered with ajax, in jQuery

- by abdullah kahraman

Hello. Let's say I have a link in "index.php", when I click on that link, it loads, via ajax, a content from a page "content.php" into a div element in "index.php", that has an id of "#content". That content in "content.php" has large images. I want to display an image loader, say "ajax-loader.gif", instead of those large images, until the images are downloaded by client. ( I know how to have an image loader .gif for the images on "index.php". ) How can I achieve this?

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JPA/Hibernate query with class name?

- by Petteri Hietavirta

In this example com.test.Cat extends com.test.Animal and there is no field DB in CAT table of com.test.Cat explicitly defining its type (it wasn't me). When I query my animals from DB I get a collection of Animals. It is possible to sort them by class name: order by r.class but is there a way to use class name as a criteria? For example I would like to get all animals expect dogs. But no luck - even this does not work: where r.class = ? (String "ccc.test.Cat") as I get an exception: Caused by: java.lang.ClassCastException: java.lang.String cannot be cast to java.lang.Integer at org.hibernate.type.IntegerType.set(IntegerType.java:64) at org.hibernate.type.NullableType.nullSafeSet(NullableType.java:154) at org.hibernate.type.NullableType.nullSafeSet(NullableType.java:136) at org.hibernate.param.PositionalParameterSpecification.bind(PositionalParameterSpecification.java:62) at org.hibernate.loader.hql.QueryLoader.bindParameterValues(QueryLoader.java:514) at org.hibernate.loader.Loader.prepareQueryStatement(Loader.java:1589) at org.hibernate.loader.Loader.doQuery(Loader.java:696) at org.hibernate.loader.Loader.doQueryAndInitializeNonLazyCollections(Loader.java:259) at org.hibernate.loader.Loader.doList(Loader.java:2228) at org.hibernate.loader.Loader.listIgnoreQueryCache(Loader.java:2125) at org.hibernate.loader.Loader.list(Loader.java:2120) at org.hibernate.loader.hql.QueryLoader.list(QueryLoader.java:401) at org.hibernate.hql.ast.QueryTranslatorImpl.list(QueryTranslatorImpl.java:361) at org.hibernate.engine.query.HQLQueryPlan.performList(HQLQueryPlan.java:196) at org.hibernate.impl.SessionImpl.list(SessionImpl.java:1148) at org.hibernate.impl.QueryImpl.list(QueryImpl.java:102) at org.hibernate.ejb.QueryImpl.getResultList(QueryImpl.java:67)

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Subclassing to avoid line length

- by Super User

The standard line length of code is 80 characters per line. This is accepted and followed by the most of programmers. I working on a state machine of a character and is necessary for me follow this too. I have four classes who pass this limit. I can subclass each class in two more and then avoid the line length limit. class Stand class Walk class Punch class Crouch The new classes would be StandLeft, StandRight and so on. Stand, Walk, Punch and Crouch would be then abstract classes. The question if there is a limit for the long of the hierarchies tree or this is depends of the case.

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c++ defining a static member of a template class with type inner class pointer

- by Jack

I have a template class like here (in a header) with a inner class and a static member of type pointer to inner class template <class t> class outer { class inner { int a; }; static inner *m; }; template <class t> outer <t>::inner *outer <t>::m; when i want to define that static member i says "error: expected constructor, destructor, or type conversion before '*' token" on the last line (mingw32-g++ 3.4.5)

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Class.Class vs Namespace.Class for top level general use class libraries?

- by Joan Venge

Which one is more acceptable (best-practice)?: namespace NP public static class IO public static class Xml ... // extension methods using NP; IO.GetAvailableResources (); vs public static class NP public static class IO public static class Xml ... // extension methods NP.IO.GetAvailableResources (); Also for #2, the code size is managed by having partial classes so each nested class can be in a separate file, same for extension methods (except that there is no nested class for them) I prefer #2, for a couple of reasons like being able to use type names that are already commonly used, like IO, that I don't want to replace or collide. Which one do you prefer? Any pros and cons for each? What's the best practice for this case? EDIT: Also would there be a performance difference between the two?

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