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  • Reference-type conversion operators: asking for trouble?

    - by Ben
    When I compile the following code using g++ class A {}; void foo(A&) {} int main() { foo(A()); return 0; } I get the following error messages: > g++ test.cpp -o test test.cpp: In function ‘int main()’: test.cpp:10: error: invalid initialization of non-const reference of type ‘A&’ from a temporary of type ‘A’ test.cpp:6: error: in passing argument 1 of ‘void foo(A&)’ After some reflection, these errors make plenty of sense to me. A() is just a temporary value, not an assignable location on the stack, so it wouldn't seem to have an address. If it doesn't have an address, then I can't hold a reference to it. Okay, fine. But wait! If I add the following conversion operator to the class A class A { public: operator A&() { return *this; } }; then all is well! My question is whether this even remotely safe. What exactly does this point to when A() is constructed as a temporary value? I am given some confidence by the fact that void foo(const A&) {} can accept temporary values according to g++ and all other compilers I've used. The const keyword can always be cast away, so it would surprise me if there were any actual semantic differences between a const A& parameter and an A& parameter. So I guess that's another way of asking my question: why is a const reference to a temporary value considered safe by the compiler whereas a non-const reference is not?

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  • Returning the same type the function was passed

    - by Ken Bloom
    I have the following code implementation of Breadth-First search. trait State{ def successors:Seq[State] def isSuccess:Boolean = false def admissableHeuristic:Double } def breadthFirstSearch(initial:State):Option[List[State]] = { val open= new scala.collection.mutable.Queue[List[State]] val closed = new scala.collection.mutable.HashSet[State] open.enqueue(initial::Nil) while (!open.isEmpty){ val path:List[State]=open.dequeue() if(path.head.isSuccess) return Some(path.reverse) closed += path.head for (x <- path.head.successors) if (!closed.contains(x)) open.enqueue(x::path) } return None } If I define a subtype of State for my particular problem class CannibalsState extends State { //... } What's the best way to make breadthFirstSearch return the same subtype as it was passed? Supposing I change this so that there are 3 different state classes for my particular problem and they share a common supertype: abstract class CannibalsState extends State { //... } class LeftSideOfRiver extends CannibalsState { //... } class InTransit extends CannibalsState { //... } class RightSideOfRiver extends CannibalsState { //... } How can I make the types work out so that breadthFirstSearch infers that the correct return type is CannibalsState when it's passed an instance of LeftSideOfRiver? Can this be done with an abstract type member, or must it be done with generics?

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  • Rails3 renders a js.erb template with a text/html content-type instead of text/javascript

    - by Yannis
    Hi, I'm building a new app with 3.0.0.beta3. I simply try to render a js.erb template to an Ajax request for the following action (in publications_controller.rb): def get_pubmed_data entry = Bio::PubMed.query(params[:pmid])# searches PubMed and get entry @publication = Bio::MEDLINE.new(entry) # creates Bio::MEDLINE object from entry text flash[:warning] = "No publication found."if @publication.title.blank? and @publication.authors.blank? and @publication.journal.blank? respond_to do |format| format.js end end Currently, my get_pubmed_data.js.erb template is simply alert('<%= @publication.title %>') The server is responding with the following alert('Evidence for a herpes simplex virus-specific factor controlling the transcription of deoxypyrimidine kinase.') which is perfectly fine except that nothing happen in the browser, probably because the content-type of the response is 'text/html' instead of 'text/javascript' as shown by the response header partially reproduced here: Status 200 Keep-Alive timeout=5, max=100 Connection Keep-Alive Transfer-Encoding chunked Content-Type text/html; charset=utf-8 Is this a bug or am I missing something? Thanks for your help!

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  • Type-safe mapping from Class<T> to Thing<T>

    - by Joonas Pulakka
    I want to make a map-kind of container that has the following interface: public <T> Thing<T> get(Class<T> clazz); public <T> void put(Class<T> clazz, Thing<T> thing); The interesting point is that the Ts in each Class<T><- Thing<T> pair is the same T, but the container should be able to hold many different types of pairs. Initially I tried a (Hash)Map. But, for instance, Map<Class<T>, Thing<T>> is not right, because then T would be same T for all pairs in that map. Of course, Map<Class<?>, Thing<?>> works, but then I don't have type-safety guarantees so that when I get(String.class), I can't be sure that I get a Thing<String> instance back. Is there a way to accomplish the kind of type safety that I'm looking for?

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  • Assign Multiple Custom User Roles to a Custom Post Type

    - by OUHSD Webmaster
    Okay here's the situation.... I'm working on a my business website. There will be a work/portfolio area. "Work" is a custom post type. "Designer" is a custom user role. "Client" is a custom user role. In creating a new "Work" post I would like to be able to select both a "designer" and "Client" to assign to the piece of work, as I would assign an author to a regular ol' post. I tried the method from this answer but it did not work for me. ) I placed it in my functions.php file. ` add_filter('wp_dropdown_users', 'test'); function test($output) { global $post; //Doing it only for the custom post type if($post->post_type == 'work') { $users = get_users(array('role'=>'designer')); //We're forming a new select with our values, you can add an option //with value 1, and text as 'admin' if you want the admin to be listed as well, //optionally you can use a simple string replace trick to insert your options, //if you don't want to override the defaults $output .= "<select id='post_author_override' name='post_author_override' class=''>"; foreach($users as $user) { $output .= "<option value='".$user->id."'>".$user->user_login."</option>"; } $output .= "</select>"; } return $output; } ` Any help would be extremely appreciated!

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  • Java Generics Class Parameter Type Inference

    - by Pindatjuh
    Given the interface: public interface BasedOnOther<T, U extends BasedList<T>> { public T getOther(); public void staticStatisfied(final U list); } The BasedOnOther<T, U extends BasedList<T>> looks very ugly in my use-cases. It is because the T type parameter is already defined in the BasedList<T> part, so the "uglyness" comes from that T needs to be typed twice. Problem: is it possible to let the Java compiler infer the generic T type from BasedList<T> in a generic class/interface definition? Ultimately, I'd like to use the interface like: class X implements BasedOnOther<BasedList<SomeType>> { public SomeType getOther() { ... } public void staticStatisfied(final BasedList<SomeType> list) { ... } } // Does not compile, due to invalid parameter count. Instead: class X implements BasedOnOther<SomeType, BasedList<SomeType>> { public SomeType getOther() { ... } public void staticStatisfied(final BasedList<SomeType> list) { ... } }

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  • Java Generics Class Type Parameter Inference

    - by Pindatjuh
    Given the interface: public interface BasedOnOther<T, U extends BasedList<T>> { public T getOther(); public void staticStatisfied(final U list); } The BasedOnOther<T, U extends BasedList<T>> looks very ugly in my use-cases. It is because the T type parameter is already defined in the BasedList<T> part, so the "uglyness" comes from that T needs to be typed twice. Problem: is it possible to let the Java compiler infer the generic T type from BasedList<T> in a generic class/interface definition? Ultimately, I'd like to use the interface like: class X extends BasedOnOther<BasedList<SomeType>> { public SomeType getOther() { ... } public void staticStatisfied(final BasedList<SomeType> list) { ... } } Instead: class X extends BasedOnOther<SomeType, BasedList<SomeType>> { public SomeType getOther() { ... } public void staticStatisfied(final BasedList<SomeType> list) { ... } }

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  • Converting string to a simple type

    - by zespri
    .Net framework contains a great class named Convert that allows conversion between simple types, DateTime type and String type. Also the class support conversion of the types implementing IConvertible interface. The class has been implemented in the very first version of .Net framework. There were a few things in the first .Net framework that were not done quite right. For example .Parse methods on simple types would throw an exception if the string couldn't be parsed and there would be no way to check if exception is going to be thrown in advance. A future version of .Net Framework removed this deficiency by introducing the TryParse method that resolved this problem. The Convert class dates back to time of the old Parse method, so the ChangeType method on this class in implemented old style - if conversion can't be performed an exception is thrown. Take a look at the following code: public static T ConvertString<T>(string s, T @default) { try { return (T)Convert.ChangeType(s, typeof(T), CultureInfo.InvariantCulture); } catch (Exception) { return @default; } } This code basically does what I want. However I would pretty much like to avoid the ugly try/catch here. I'm sure, that similar to TryParse, there is a modern method of rewriting this code without the catch-all. Could you suggest one?

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  • C# Type conversion between two similar Datatable objects

    - by Ali
    I have .NET project with sync framework and two separate Datasets for MS SQL and Compact SQL. in my base class I have a generic DataTable object. in my derived classed I assign Typed DataTable to the generic object based on whether the application is operating online or offline: example: if (online) _dataTable = new MSSQLDataSet.Customer; else _dataTable = new CompactSQLDataSet.Customer; Now every where in my code i have to check and do a cast based on the current network mode like this: public void changeCustomerID(int ID) { if (online) (MSSQLDataSet.CustomerDataTable)_dataTable)[i].CustomerID = value; else (CompactMSSQLDataSet.CustomerDataTable)_dataTable)[i].CustomerID = value; } but I don't think this is very efficient and I believe it can be done in a smarter way to only use one line of code by dynamically getting the Type of _dataTable on the run time. my problem is at the design time, in order to acess datatable porperties such as "CustomerID" it has to be casted to either MSSQLDataSet.CustomerDataTable or CompactMSSQLDataSet.CustomerDataTable. Is there a way to have a function or a operator to convert the _datatable to its runtime type but still be able to use it's design time properties which are the same between the two types? something like: ((aType)_dataTable)[i].CustomerID = value; //or GetRuntimeType(_dataTable)[i].CustomerID = value;

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  • C# - Calling ToString() on a Reference Type

    - by nfplee
    Given two object arrays I need to compare the differences between the two (when converted to a string). I've reduced the code to the following and the problem still exists: public void Compare(object[] array1, object[] array2) { for (var i = 0; i < array1.Length; i++) { var value1 = GetStringValue(array1[i]); var value2 = GetStringValue(array2[i]); } } public string GetStringValue(object value) { return value != null && value.ToString() != string.Empty ? value.ToString() : ""; } The code executes fine no matter what object arrays I throw at it. However if one of the items in the array is a reference type then somehow the reference is updated. This causes issues later. It appears that this happens when calling ToString() against the object reference. I have updated the GetStringValue method to the following (which makes sure the object is either a value type or string) and the problem goes away. public string GetStringValue(object value) { return value != null && (value.GetType().IsValueType || value is string) && value.ToString() != string.Empty ? value.ToString() : ""; } However this is just a temporary hack as I'd like to be able to override the ToString() method on my reference types and compare them as well. I'd appreciate it if someone could explain why this is happening and offer a potential solution. Thanks

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  • Compile time type determination in C++

    - by dicroce
    A coworker recently showed me some code that he found online. It appears to allow compile time determination of whether a type has an "is a" relationship with another type. I think this is totally awesome, but I have to admit that I'm clueless as to how this actually works. Can anyone explain this to me? template<typename BaseT, typename DerivedT> inline bool isRelated(const DerivedT&) { DerivedT derived(); char test(const BaseT&); // sizeof(test()) == sizeof(char) char (&test(...))[2]; // sizeof(test()) == sizeof(char[2]) struct conversion { enum { exists = (sizeof(test(derived())) == sizeof(char)) }; }; return conversion::exists; } Once this function is defined, you can use it like this: #include <iostream> class base {}; class derived : public base {}; class unrelated {}; int main() { base b; derived d; unrelated u; if( isRelated<base>( b ) ) std::cout << "b is related to base" << std::endl; if( isRelated<base>( d ) ) std::cout << "d is related to base" << std::endl; if( !isRelated<base>( u ) ) std::cout << "u is not related to base" << std::endl; }

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  • Torchlight Black Screen and doesn't show up

    - by Lelouch Reyiz
    When I open it in full screen I get a black screen that covers whole screen,in windowed mode middle of screen.Here is a video: https://copy.com/fvrGw7QIJ8Z0 Terminal Output: alperen@alperen-Inspiron-N5010 /usr/local/games/Torchlight $ ./Torchlight.bin.x86_64 Creating resource group General Creating resource group Internal Creating resource group Autodetect SceneManagerFactory for type 'DefaultSceneManager' registered. Registering ResourceManager for type Material Registering ResourceManager for type Mesh Registering ResourceManager for type Skeleton MovableObjectFactory for type 'ParticleSystem' registered. OverlayElementFactory for type Panel registered. OverlayElementFactory for type BorderPanel registered. OverlayElementFactory for type TextArea registered. Registering ResourceManager for type Font ArchiveFactory for archive type FileSystem registered. ArchiveFactory for archive type Zip registered. FreeImage version: 3.13.1 This program uses FreeImage, a free, open source image library supporting all common bitmap formats. See http://freeimage.sourceforge.net for details Supported formats: bmp,ico,jpg,jif,jpeg,jpe,jng,koa,iff,lbm,mng,pbm,pbm,pcd,pcx,pgm,pgm,png,ppm,ppm,ras,tga,targa,tif,tiff,wap,wbmp,wbm,psd,cut,xbm,xpm,gif,hdr,g3,sgi,exr,j2k,j2c,jp2,pfm,pct,pict,pic,bay,bmq,cr2,crw,cs1,dc2,dcr,dng,erf,fff,hdr,k25,kdc,mdc,mos,mrw,nef,orf,pef,pxn,raf,raw,rdc,sr2,srf,arw,3fr,cine,ia,kc2,mef,nrw,qtk,rw2,sti,drf,dsc,ptx,cap,iiq,rwz DDS codec registering Registering ResourceManager for type HighLevelGpuProgram Registering ResourceManager for type Compositor MovableObjectFactory for type 'Entity' registered. MovableObjectFactory for type 'Light' registered. MovableObjectFactory for type 'BillboardSet' registered. MovableObjectFactory for type 'ManualObject' registered. MovableObjectFactory for type 'BillboardChain' registered. MovableObjectFactory for type 'RibbonTrail' registered. Loading library lib64/OGRE/RenderSystem_GL Installing plugin: GL RenderSystem OpenGL Rendering Subsystem created. Plugin successfully installed Loading library lib64/OGRE/Plugin_ParticleFX Installing plugin: ParticleFX Particle Emitter Type 'Point' registered Particle Emitter Type 'Box' registered Particle Emitter Type 'Ellipsoid' registered Particle Emitter Type 'Cylinder' registered Particle Emitter Type 'Ring' registered Particle Emitter Type 'HollowEllipsoid' registered Particle Affector Type 'LinearForce' registered Particle Affector Type 'ColourFader' registered Particle Affector Type 'ColourFader2' registered Particle Affector Type 'ColourImage' registered Particle Affector Type 'ColourInterpolator' registered Particle Affector Type 'Scaler' registered Particle Affector Type 'Rotator' registered Particle Affector Type 'DirectionRandomiser' registered Particle Affector Type 'DeflectorPlane' registered Plugin successfully installed Loading library lib64/OGRE/Plugin_OctreeSceneManager Installing plugin: Octree & Terrain Scene Manager Plugin successfully installed *-*-* OGRE Initialising *-*-* Version 1.6.5 (Shoggoth) terminate called after throwing an instance of 'std::out_of_range' what(): basic_string::substr Error: signal: 6 ./Torchlight.bin.x86_64(_ZN10LinuxUtils13crash_handlerEi+0x25)[0x17eb6f5] /lib/x86_64-linux-gnu/libc.so.6(+0x37000)[0x7fc647877000] /lib/x86_64-linux-gnu/libc.so.6(gsignal+0x39)[0x7fc647876f89] /lib/x86_64-linux-gnu/libc.so.6(abort+0x148)[0x7fc64787a398] /usr/lib/x86_64-linux-gnu/libstdc++.so.6(_ZN9__gnu_cxx27__verbose_terminate_handlerEv+0x155)[0x7fc6481826b5] /usr/lib/x86_64-linux-gnu/libstdc++.so.6(+0x5e836)[0x7fc648180836] /usr/lib/x86_64-linux-gnu/libstdc++.so.6(+0x5e863)[0x7fc648180863] /usr/lib/x86_64-linux-gnu/libstdc++.so.6(+0x5eaa2)[0x7fc648180aa2] /usr/lib/x86_64-linux-gnu/libstdc++.so.6(_ZSt20__throw_out_of_rangePKc+0x67)[0x7fc6481d25d7] /usr/lib/x86_64-linux-gnu/libstdc++.so.6(+0xbe3d3)[0x7fc6481e03d3] ./Torchlight.bin.x86_64(_ZN11CFileSystem21buildMassiveDataGroupEv+0x453)[0x1617805] ./Torchlight.bin.x86_64(_ZN11CFileSystemC1Eb+0x14be)[0x16145ae] ./Torchlight.bin.x86_64(_ZN22CMasterResourceManagerC1EP9CSettings+0x41a)[0xfe1d0a] ./Torchlight.bin.x86_64(_ZN5CGame5setupEb+0x79a)[0x73ceaa] ./Torchlight.bin.x86_64(_ZN5CGame5beginEPv+0x28d)[0x73b839] ./Torchlight.bin.x86_64(main+0x649)[0x146dbe4] /lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0xf5)[0x7fc647861ec5] ./Torchlight.bin.x86_64[0x739ca9]

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  • eclipse 3.4 (ganymede) package collision with type

    - by Monis Iqbal
    We have a package that ends with exception e.g. package a.b.c.exception; Our code base had no issues up till eclipse 3.3, however when we shifted to eclipse 3.4, it started giving errors related to this package: "The package a.b.c.exception collides with a type" When I refactor the package name to a.b.c.exceptions, there are no issues. Is this due to a bug in eclipse 3.4 or is there some setting to rectify this behavior?

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  • Type hinting in Python

    - by pingvinus
    I'm studying Python after a lot of PHP experience and it would be handy to have type-hinting in Python. Looks like eclipse + pydev doesn't support this. Any suggestions? For example, I want my IDE to show function docstrings and types, when I use it, like: def f(x: int) -> int: r"""Adds 3 to x""" return x + 3 f( #and now IDE shows everything about types

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  • wordpress custom post type

    - by codedude
    So I've just made a custom post type for my wordpress theme named "Products". When I create a new post in it and view it, the link is something like this: "http://localhost/wordpress/product/a-product-title" This page views as expected but when I try to go to the supposed parent page: "http://localhost/wordpress/product/" I get a 404 error page. Is there a special template I need to make to view this page? Thanks

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  • Can a single argument constructor with a default value be subject to implicit type conversion

    - by Richard
    I understand the use of the explicit keyword to avoid the implicit type conversions that can occur with a single argument constructor, or with a constructor that has multiple arguments of which only the first does not have a default value. However, I was wondering, does a single argument constructor with a default value behave the same as one without a default value when it comes to implicit conversions?

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  • Generic Type constraint in .net

    - by Jose
    Okay I'm looking for some input, I'm pretty sure this is not currently supported in .NET 3.5 but here goes. I want to require a generic type passed into my class to have a constructor like this: new(IDictionary<string,object>) so the class would look like this public MyClass<T> where T : new(IDictionary<string,object>) { T CreateObject(IDictionary<string,object> values) { return new T(values); } } But the compiler doesn't support this, it doesn't really know what I'm asking. Some of you might ask, why do you want to do this? Well I'm working on a pet project of an ORM so I get values from the DB and then create the object and load the values. I thought it would be cleaner to allow the object just create itself with the values I give it. As far as I can tell I have two options: 1) Use reflection(which I'm trying to avoid) to grab the PropertyInfo[] array and then use that to load the values. 2) require T to support an interface like so: public interface ILoadValues { void LoadValues(IDictionary values); } and then do this public MyClass<T> where T:new(),ILoadValues { T CreateObject(IDictionary<string,object> values) { T obj = new T(); obj.LoadValues(values); return obj; } } The problem I have with the interface I guess is philosophical, I don't really want to expose a public method for people to load the values. Using the constructor the idea was that if I had an object like this namespace DataSource.Data { public class User { protected internal User(IDictionary<string,object> values) { //Initialize } } } As long as the MyClass<T> was in the same assembly the constructor would be available. I personally think that the Type constraint in my opinion should ask (Do I have access to this constructor? I do, great!) Anyways any input is welcome.

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  • Flash type casting gone wrong

    - by Malfist
    Sorry, I'm new to flash I have this line of code: BaseEntry( _entryList[i] ).topTeamName = ((Team)(teamList.getNameAtIndex( i*2 ))).Name; and I get the error: TypeError: Error #1034: Type Coercion failed: cannot convert "[object Team]" to ncaa.Data.Team. What do I need to do to fix it?

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  • What is correct content-type for excel files?

    - by taw
    I want excel files on a website to open in Excel when clicked, not get saved on desktop, or get opened embedded in a browser etc. Now obviously it all depends on how everything is configured for each user, but what's the best Content-Type and other settings to achieve just that most of the time?

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  • Scala: how to specify varargs as type?

    - by IttayD
    Instead of def foo(configuration: (String, String)*) I'd like to be able to write: type Configuration = (String, String)* def foo(configuration: Configuration) The main use case is to provide an easy method signature when overriding in subclasses

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