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  • Why isn't the compiler smarter in this const function overloading problem?

    - by Frank
    The following code does not compile: #include <iostream> class Foo { std::string s; public: const std::string& GetString() const { return s; } std::string* GetString() { return &s; } }; int main(int argc, char** argv){ Foo foo; const std::string& s = foo.GetString(); // error return 0; } I get the following error: const1.cc:11: error: invalid initialization of reference of type 'const std::string&' from expression of type 'std::string* It does make some sense because foo is not of type const Foo, but just Foo, so the compiler wants to use the non-const function. But still, why can't it recognize that I want to call the const GetString function, by looking at the (type of) variable I assign it to? I found this kind of surprising.

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  • Retrieving Custom Attributes Using Reflection

    - by Scott Dorman
    The .NET Framework allows you to easily add metadata to your classes by using attributes. These attributes can be ones that the .NET Framework already provides, of which there are over 300, or you can create your own. Using reflection, the ways to retrieve the custom attributes of a type are: System.Reflection.MemberInfo public abstract object[] GetCustomAttributes(bool inherit); public abstract object[] GetCustomAttributes(Type attributeType, bool inherit); public abstract bool IsDefined(Type attributeType, bool inherit); System.Attribute public static Attribute[] GetCustomAttributes(MemberInfo member, bool inherit); public static bool IsDefined(MemberInfo element, Type attributeType, bool inherit); If you take the following simple class hierarchy: public abstract class BaseClass { private bool result;   [DefaultValue(false)] public virtual bool SimpleProperty { get { return this.result; } set { this.result = value; } } }   public class DerivedClass : BaseClass { public override bool SimpleProperty { get { return true; } set { base.SimpleProperty = value; } } } Given a PropertyInfo object (which is derived from MemberInfo, and represents a propery in reflection), you might expect that these methods would return the same result. Unfortunately, that isn’t the case. The MemberInfo methods strictly reflect the metadata definitions, ignoring the inherit parameter and not searching the inheritance chain when used with a PropertyInfo, EventInfo, or ParameterInfo object. It also returns all custom attribute instances, including those that don’t inherit from System.Attribute. The Attribute methods are closer to the implied behavior of the language (and probably closer to what you would naturally expect). They do respect the inherit parameter for PropertyInfo, EventInfo, and ParameterInfo objects and search the implied inheritance chain defined by the associated methods (in this case, the property accessors). These methods also only return custom attributes that inherit from System.Attribute. This is a fairly subtle difference that can produce very unexpected results if you aren’t careful. For example, to retrieve the custom  attributes defined on SimpleProperty, you could use code similar to this: PropertyInfo info = typeof(DerivedClass).GetProperty("SimpleProperty"); var attributeList1 = info.GetCustomAttributes(typeof(DefaultValueAttribute), true)); var attributeList2 = Attribute.GetCustomAttributes(info, typeof(DefaultValueAttribute), true));   The attributeList1 array will be empty while the attributeList2 array will contain the attribute instance, as expected. Technorati Tags: Reflection,Custom Attributes,PropertyInfo

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  • How to convert a lambda to an std::function using templates

    - by retep998
    Basically, what I want to be able to do is take a lambda with any number of any type of parameters and convert it to an std::function. I've tried the following and neither method works. std::function([](){});//Complains that std::function is missing template parameters template <typename T> void foo(function<T> f){} foo([](){});//Complains that it cannot find a matching candidate The following code does work however, but it is not what I want because it requires explicitly stating the template parameters which does not work for generic code. std::function<void()>([](){}); I've been mucking around with functions and templates all evening and I just can't figure this out, so any help would be much appreciated. As mentioned in a comment, the reason I'm trying to do this is because I'm trying to implement currying in C++ using variadic templates. Unfortunately, this fails horribly when using lambdas. For example, I can pass a standard function using a function pointer. template <typename R, typename...A> void foo(R (*f)(A...)) {} void bar() {} int main() { foo(bar); } However, I can't figure out how to pass a lambda to such a variadic function. Why I'm interested in converting a generic lambda into an std::function is because I can do the following, but it ends up requiring that I explicitly state the template parameters to std::function which is what I am trying to avoid. template <typename R, typename...A> void foo(std::function<R(A...)>) {} int main() { foo(std::function<void()>([](){})); }

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  • How to change password on RAR archive w/o modifying arch. files attributes (modified/created)?

    - by Larry78
    How do I change the password of an .RAR archive, without changing the date/time attributes of the files in the archive? Unfortunately you can't directly change the password of the archive with WinRAR, you have to extract the files, and then make a new archive with the new password. So the created/modified attributes of the files in the archive get changed. I know you can manually change the attributes of a file with available utilities - but there are hundreds of files in the archive, each with unique attributes, so it would take a very long time to "fix" each file before re-archiving it. I'm using WinRAR 3.51, the last free version. Windows XP Pro SP3. Update: I don't care if the output is a .RAR file or a ZIP file IZArc4.1 will convert the RAR to a ZIP, and it keeps the dates. The problem is it compresses the file - there isn't a "store" option, and setting the default to store in the main configuration doesn't effect conversions. The RAR contains uncompressed files. None of these other archiving programs will even do a conversion. A couple claim to, or try to, but the errors returned indicate a very lousy application. So far I've tried PeaZip, 7-Zip, FilZip, TugZip, SimplyZipSE, QuickZip, and WinShrink (from downloads.cnet.com). WinRAR gives the error "skipping encryped archive" when I try the conversion. It asks for the password first, and I know it's right, as I opened the archive, and I can read/view all the files in it. It works on non-encrypted files.

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  • Pass a function as parameter in jQuery?

    - by thedp
    Hello, I would like to pass to a jQuery function a regular function, instead of the usual anonymous function, but I'm not sure how such a thing could be done. Instead of this: function setVersion(feature) { $.post("some.php", { abc:"abc" }, function(data){ // do something here }, "json"); } I would like to do this: function foo(data){ // do something here } function setVersion(feature) { $.post("some.php", { abc:"abc" }, foo, "json"); } Thank you.

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  • Sorting deeply nested attributes in Rails

    - by Senthil
    I want to be able to drag and drag App model which is nested under Category model. http://railscasts.com/episodes/196-nested-model-form-part-1 's the Railscast I've tried to follow. Category controller def move params[:apps].each_with_index do |id, index| Category.last.apps.update(['position=?', index+1], ['id=?', Category.last.id]) end render :nothing => true end I'm able to sort Categories with something similar, but since I'm updating an attribute, I'm having trouble. def sort params[:categories].each_with_index do |id, index| Category.update_all(['position=?', index+1], ['id=?', id]) end render :nothing => true end Any help is appreciated.

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  • XStream parse attributes and values at the same time

    - by gurbieta
    Hi, I have the following XML <search ver="3.0"> <loc id="ARBA0009" type="1">Buenos Aires, Argentina</loc> <loc id="BRXX1283" type="1">Buenos Aires, Brazil</loc> <loc id="ARDF0127" type="1">Aeroparque Buenos Aires, Argentina</loc> <loc id="MXJO0669" type="1">Concepcion De Buenos Aires, Mexico</loc> <loc id="MXPA1785" type="1">San Nicolas De Buenos Aires, Mexico</loc> <loc id="ARBA0005" type="1">Balcarce, Argentina</loc> <loc id="ARBA0008" type="1">Bragado, Argentina</loc> <loc id="ARBA0010" type="1">Campana, Argentina</loc> <loc id="ARBA0016" type="1">Chascomus, Argentina</loc> <loc id="ARBA0019" type="1">Chivilcoy, Argentina</loc> </search> And a City class public class City { private String id; private Integer type; private String name; // getters & setters... } I tried the following aliases to parse the XML xStream.alias("search", List.class); xStream.alias("loc", City.class); xStream.useAttributeFor("id", String.class); xStream.useAttributeFor("type", Integer.class); But I can't figure out how to set the value of the "loc" tag, if I try to transform the City object in XML I get <search> <loc id="ARBA0001" type="1"> <name>Buenos Aires</name> </loc> </search> When I really need to get this <search> <loc id="ARBA0001" type="1">Buenos Aires</loc> </search> Then, if I try to parse the XML to a City object I get the field "name" with a null value. Anybody knows how to set te correct aliases to do this? Thanks in advance.

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  • Reflection, get DataAnnotation attributes from buddy class.

    - by Feryt
    Hi. I need to check if property has specific attribute defined in its buddy class: [MetadataType(typeof(Metadata))] public sealed partial class Address { private sealed class Metadata { [Required] public string Address1 { get; set; } [Required] public string Zip { get; set; } } } How to check what properties has defined Required attribute? Thank you.

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  • Xpath that evaluates -all- attributes?

    - by Tres
    I maybe be trying to do something invalid here, but maybe someone smarter than me knows the correct syntax to solve my problem. Given: <group code="vehicle"> <line code="car"> <cell> <box code="price">1000.00</box> </cell> </line> <line code="car"> <cell code="sports"> <box code="price">500.00</box> </cell> </line> </group> If I use //*[@code="vehicle"]//*[@code="car"]//*[@code="price"], I will get both boxes returned (1000.00 and 500.00)--as expected but not what I want. Is there an xpath syntax that will evaluate against all nodes that have an attribute of @code rather than skipping it if it doesn't match with the end result being that I only get back the first box (price of 1000.00)? Like asking, choose the first node with @code and that @code must equal "vehicle", then choose the next node with @code and that @code must equal "car", then choose the next node with @code and @code must equal "price".

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  • Nested attributes in the index view?

    - by user283179
    How would I show one of many nested objects in the index view class Album < ActiveRecord::Base has_many: photos accepts_nested_attributes_for :photos, :reject_if => proc { |a| a.all? { |k, v| v.blank?} } has_one: cover accepts_nested_attributes_for :cover end class Album Controller < ApplicationController layout "mini" def index @albums = Album.find(:all, :include => [:cover,]).reverse respond_to do |format| format.html # index.html.erb format.xml { render :xml => @albums } end end This is what I have so fare. I just want to show a cover for each album. Any info on this would be a massive help!!

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  • nested attributes with polymorphic has_one model

    - by Millisami
    I am using accepts_nested_attributes_for with the has_one polymorphic model in rails 2.3.5 Following are the models and its associations: class Address < ActiveRecord::Base attr_accessible :city, :address1, :address2 belongs_to :addressable, :polymorphic => true validates_presence_of :address1, :address2, :city end class Vendor < ActiveRecord::Base attr_accessible :name, :address_attributes has_one :address, :as => :addressable, :dependent => :destroy accepts_nested_attributes_for :address end This is the view: - form_for @vendor do |f| = f.error_messages %p = f.label :name %br = f.text_field :name - f.fields_for :address_attributes do |address| = render "shared/address_fields", :f => address %p = f.submit "Create" This is the partial shared/address_fields.html.haml %p = f.label :city %br= f.text_field :city %span City/Town name like Dharan, Butwal, Kathmandu, .. %p = f.label :address1 %br= f.text_field :address1 %span City Street name like Lazimpat, New Road, .. %p = f.label :address2 %br= f.text_field :address2 %span Tole, Marg, Chowk name like Pokhrel Tole, Shanti Marg, Pako, .. And this is the controller: class VendorsController < ApplicationController def new @vendor = Vendor.new end def create @vendor = Vendor.new(params[:vendor]) if @vendor.save flash[:notice] = "Vendor created successfully!" redirect_to @vendor else render :action => 'new' end end end The problem is when I fill in all the fileds, the record gets save on both tables as expected. But when I just the name and city or address1 filed, the validation works, error message shown, but the value I put in the city or address1, is not persisted or not displayed inside the address form fields? This is the same case with edit action too. Though the record is saved, the address doesn't show up on the edit form. Only the name of the Client model is shown. Actually, when I look at the log, the address model SQL is not queried even at all.

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  • IDE underlining custom attributes

    - by runrunraygun
    I have a custom attribute... [System.AttributeUsage(System.AttributeTargets.All)] public class Refactor : System.Attribute { private string _message; public Refactor() { _message = string.Empty; } public Refactor(string message) { _message = message; } } Applied to [Refactor("this should be less rubbish")] public virtual void RubbishMethod() { … } Now when someone makes a call to RubbishMethod I'd like the IDE (vs2008) to underline that call in a deep brown colour, similar to if I mark as Obsolete you get a green wave line. Is this possible? I've been racking my brain and hitting the google but I can't find how and where to do this.

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  • Copy constructor using private attributes

    - by Pedro Magueija
    Hello all, My first question here so be gentle. I would like arguments for the following code: public class Example { private String name; private int age; ... // copy constructor here public Example(Example e) { this.name = e.name; // accessing a private attribute of an instance this.age = e.age; } ... } I believe this breaks the modularity of the instance passed to the copy construct. This is what I believe to be correct: public class Example { private String name; private int age; ... // copy constructor here public Example(Example e) { this.setName(e.getName()); this.setAge(e.getAge()); } ... } A friend has exposed a valid point of view, saying that in the copy construct we should create the object as fast as possible. And adding getter/setter methods would result in unnecessary overhead. I stand on a crossroad. Can you shed some light?

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  • Function arguments VBA

    - by user1068249
    I have these three functions: When I run the first 2 functions, There's no problem, but when I run the last function (LMTD), It says 'Division by zero' yet when I debug some of the arguments have values, some don't. I know what I have to do, but I want to know why I have to do it, because it makes no sense to me. Tinn-function doesn't have Tut's arguments, so I have to add them to Tinn-function's arguments. Same goes for Tut, that doesn't know all of Tinn's arguments, and LMTD has to have both of Tinn and Tut's arguments. If I do that, it all runs smoothly. Why do I have to do this? Public Function Tinn(Tw, Qw, Qp, Q, deltaT) Tinn = (((Tw * Qw) + (Tut(Q, fd, mix) * Q)) / Qp) + deltaT End Function Public Function Tut(Q, fd, mix) Tut = Tinn(Tw, Qw, Qp, Q, deltaT) - (avgittEffektAiUiLMTD() / ((Q * fd * mix) / 3600)) End Function Public Function LMTD(Tsjo) LMTD = ((Tinn(Tw, Qw, Qp, Q, deltaT) - Tsjo) - (Tut(Q, fd, mix) - Tsjo)) / (WorksheetFunction.Ln ((Tinn(Tw, Qw, Qp, Q, deltaT) - Tsjo) / (Tut(Q, fd, mix) - Tsjo))) End Function

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  • Initialize virtual attributes

    - by Horace Loeb
    I have an IncomingEmail model with an attachments virtual attribute: class IncomingEmail < ActiveRecord::Base attr_accessor :attachments end I want the attachments virtual attribute to be initialized to [] rather than nil so that I can do: >> i = IncomingEmail.new => #<IncomingEmail id: nil,...) >> i.attachments << "whatever" Without first setting i.attachments to [] (put another way, I want this virtual attribute to default to an empty array rather than nil)

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  • has_one | nested attributes -

    - by user283179
    How would I show one of many nested objects in the index view class Album < ActiveRecord::Base has_many: photos accepts_nested_attributes_for :photos, :reject_if => proc { |a| a.all? { |k, v| v.blank?} } has_one: cover accepts_nested_attributes_for :cover end class Album Controller < ApplicationController layout "mini" def index @albums = Album.find(:all, :include => [:cover,]).reverse respond_to do |format| format.html # index.html.erb format.xml { render :xml => @albums } end end This is what I have so fare. I just want to show a cover for each album. Any info on this would be a massive help!!

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  • J2EE: Default values for custom tag attributes

    - by Nick
    So according to Sun's J2EE documentation (http://docs.sun.com/app/docs/doc/819-3669/bnani?l=en&a=view), "If a tag attribute is not required, a tag handler should provide a default value." My question is how in the hell do I define a default value as per the documentation's description. Here's the code: <%@ attribute name="visible" required="false" type="java.lang.Boolean" %> <c:if test="${visible}"> My Tag Contents Here </c:if> Obviously, this tag won't compile because it's lacking the tag directive and the core library import. My point is that I want the "visible" property to default to TRUE. The "tag attribute is not required," so the "tag handler should provide a default value." I want to provide a default value, so what am I missing? Any help is greatly appreciated.

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  • Rails Nested Attributes, Relationship for Shared or Common Object

    - by SooDesuNe
    This has to be a common problem, so I'm surprised that Google didn't turn up more answers. I'm working on a rails app that has several different kinds of entities, those entities by need a relation to a different entity. For example: Address: a Model that stores the details of a street address (this is my shared entity) PersonContact: a Model that includes things like home phone, cell phone and email address. This model needs to have an address associated with it DogContact: Obviously, if you want to contact a dog, you have to go to where it lives. So, PersonContact and DogContact should have foreign keys to Address. Even, though they are really the "owning" object of Address. This would be fine, except that accepts_nested_attributes_for is counting on the foreign key being in Address to work correctly. What's the correct strategy to keep the foreign key in Address, but have PersonContact and DogContact be the owning objects?

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  • How does dereferencing of a function pointer happen?

    - by eSKay
    Why and how does dereferencing a function pointer just "do nothing"? This is what I am talking about: #include<stdio.h> void hello() { printf("hello"); } int main(void) { (*****hello)(); } From a comment over here: function pointers dereference just fine, but the resulting function designator will be immediately converted back to a function pointer And from an answer here: Dereferencing (in way you think) a function's pointer means: accessing a CODE memory as it would be a DATA memory. Function pointer isn't suppose to be dereferenced in that way. Instead, it is called. I would use a name "dereference" side by side with "call". It's OK. Anyway: C is designed in such a way that both function name identifier as well as variable holding function's pointer mean the same: address to CODE memory. And it allows to jump to that memory by using call () syntax either on an identifier or variable. How exactly does dereferencing of a function pointer work?

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