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  • Loosely coupled implicit conversion

    - by ltjax
    Implicit conversion can be really useful when types are semantically equivalent. For example, imagine two libraries that implement a type identically, but in different namespaces. Or just a type that is mostly identical, except for some semantic-sugar here and there. Now you cannot pass one type into a function (in one of those libraries) that was designed to use the other, unless that function is a template. If it's not, you have to somehow convert one type into the other. This should be trivial (or otherwise the types are not so identical after-all!) but calling the conversion explicitly bloats your code with mostly meaningless function-calls. While such conversion functions might actually copy some values around, they essentially do nothing from a high-level "programmers" point-of-view. Implicit conversion constructors and operators could obviously help, but they introduce coupling, so that one of those types has to know about the other. Usually, at least when dealing with libraries, that is not the case, because the presence of one of those types makes the other one redundant. Also, you cannot always change libraries. Now I see two options on how to make implicit conversion work in user-code: The first would be to provide a proxy-type, that implements conversion-operators and conversion-constructors (and assignments) for all the involved types, and always use that. The second requires a minimal change to the libraries, but allows great flexibility: Add a conversion-constructor for each involved type that can be externally optionally enabled. For example, for a type A add a constructor: template <class T> A( const T& src, typename boost::enable_if<conversion_enabled<T,A>>::type* ignore=0 ) { *this = convert(src); } and a template template <class X, class Y> struct conversion_enabled : public boost::mpl::false_ {}; that disables the implicit conversion by default. Then to enable conversion between two types, specialize the template: template <> struct conversion_enabled<OtherA, A> : public boost::mpl::true_ {}; and implement a convert function that can be found through ADL. I would personally prefer to use the second variant, unless there are strong arguments against it. Now to the actual question(s): What's the preferred way to associate types for implicit conversion? Are my suggestions good ideas? Are there any downsides to either approach? Is allowing conversions like that dangerous? Should library implementers in-general supply the second method when it's likely that their type will be replicated in software they are most likely beeing used with (I'm thinking of 3d-rendering middle-ware here, where most of those packages implement a 3D vector).

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  • JNA array structure

    - by Burny
    I want to use a dll (IEC driver) in Java, for that I am using JNA. The problem in pseudo code: start the server allocate new memory for an array (JNA) client connect writing values from an array to the memory sending this array to the client client disconnect new client connect allocate new memory for an array (JNA) - JVM crash (EXCEPTION_ACCESS_VIOLATION) The JVM crash not by primitve data types and if the values will not writing from the array to the memory. the code in c: struct DataAttributeData CrvPtsArrayDAData = {0}; CrvPtsArrayDAData.ucType = DATATYPE_ARRAY; CrvPtsArrayDAData.pvData = XYValDAData; XYValDAData[0].ucType = FLOAT; XYValDAData[0].uiBitLength = sizeof(Float32)*8; XYValDAData[0].pvData = &(inUpdateValue.xVal); XYValDAData[1].ucType = FLOAT; XYValDAData[1].uiBitLength = sizeof(Float32)*8; XYValDAData[1].pvData = &(inUpdateValue.yVal); Send(&CrvPtsArrayDAData, 1); the code in Java: DataAttributeData[] data_array = (DataAttributeData[]) new DataAttributeData() .toArray(d.bitLength); for (DataAttributeData d_temp : data_array) { d_temp.data = new Memory(size / 8); d_temp.type = type_iec; d_temp.bitLength = size; d_temp.write(); } d.data = data_array[0].getPointer(); And then writing values whith this code: for (int i = 0; i < arraySize; i++) { DataAttributeData dataAttr = new DataAttributeData(d.data.share(i * d.size())); dataAttr.read(); dataAttr.data.setFloat(0, f[i]); dataAttr.write(); } the struct in c: struct DataAttributeData{ unsigned char ucType; int iArrayIndex; unsigned int uiBitLength; void * pvData;}; the struct in java: public static class DataAttributeData extends Structure { public DataAttributeData(Pointer p) { // TODO Auto-generated constructor stub super(p); } public DataAttributeData() { // TODO Auto-generated constructor stub super(); } public byte type; public int iArrayIndex; public int bitLength; public Pointer data; @Override protected List<String> getFieldOrder() { // TODO Auto-generated method stub return Arrays.asList(new String[] { "type", "iArrayIndex", "bitLength", "data" }); } } Can anybody help me?

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  • Exception throws: encapsulate them or not?

    - by Simon
    Hi there. Once I read an MSDN article that encouraged the following programming paradigm: public class MyClass { public void Method1() { NewCustomException(); } public void Method2() { NewCustomException(); } void NewCustomException() { throw new CustomException("Exception message"); } } Do you think this paradigm makes sense? Wouldn't it be enough to store the exception message in a static const field and then pass it to the exception's constructor, instead of encapsulating the whole exception throw?

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  • Multiple Timers with setTimeInterval

    - by visibleinvisibly
    I am facing a problem with setInterval being used in a loop. I have a function subscribeFeed( ) which takes an array of urls as input. It loops through the url array and subscribes each url to getFeedAutomatically() using a setInterval function. so if three URL's are there in the array, then 3 setInterval's will be called. The problem is 1)how to distinguish which setInterval is called for which URL. 2)it is causing Runtime exception in setInterval( i guess because of closure problem in javascript) //constructor function myfeed(){ this.feedArray = []; } myfeed.prototype.constructor= myfeed; myfeed.prototype.subscribeFeed =function(feedUrl){ var i=0; var url; var count = 0; var _this = this; var feedInfo = { url : [], status : "" }; var urlinfo = []; feedUrl = (feedUrl instanceof Array) ? feedUrl : [feedUrl]; //notifyInterval = (notifyInterval instanceof Array) ? notifyInterval: [notifyInterval]; for (i = 0; i < feedUrl.length; i++) { urlinfo[i] = { url:'', notifyInterval:5000,// Default Notify/Refresh interval for the feed isenable:true, // true allows the feed to be fetched from the URL timerID: null, //default ID is null called : false, position : 0, getFeedAutomatically : function(url){ _this.getFeedUpdate(url); }, }; urlinfo[i].url = feedUrl[i].URL; //overide the default notify interval if(feedUrl[i].NotifyInterval /*&& (feedUrl[i] !=undefined)*/){ urlinfo[i].notifyInterval = feedUrl[i].NotifyInterval; } // Trigger the Feed registered event with the info about URL and status feedInfo.url[i] = feedUrl[i].URL; //Set the interval to get the feed. urlinfo[i].timerID = setInterval(function(){ urlinfo[i].getFeedAutomatically(urlinfo[i].url); }, urlinfo[i].notifyInterval); this.feedArray.push(urlinfo[i]); } } // The getFeedUpate function will make an Ajax request and coninue myfeed.prototype.getFeedUpdate = function( ){ } I am posting the same on jsfiddle http://jsfiddle.net/visibleinvisibly/S37Rj/ Thanking you in advance

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  • More trivia than really important: Why no new() constraint on Activator.CreateInstance<T>() ?

    - by flq
    I think there are people who may be able to answer this, this is a question out of curiosity: The generic CreateInstance method from System.Activator, introduced in .NET v2 has no type constraints on the generic argument but does require a default constructor on the activated type, otherwise a MissingMethodException is thrown. To me it seems obvious that this method should have a type constraint like Activator.CreateInstance<T>() where T : new() { ... } Just an omission or some anecdote lurking here?

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  • How do I translate a ISO 8601 datetime string into a Python datetime object?

    - by Andrey Fedorov
    I'm getting a datetime string in a format like "2009-05-28T16:15:00" (this is ISO 8601, I believe) one hack-ish option seems to be to parse the string using time.strptime and passing the first 6 elements of the touple into the datetime constructor, like: datetime.datetime(*time.strptime("2007-03-04T21:08:12", "%Y-%m-%dT%H:%M:%S")[:6]) I haven't been able to find a "cleaner" way of doing this, is there one?

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  • Java homework help, Error <identifier> expected

    - by user2900126
    Help with java homework this is my assignment that I have, this assignment code I've tried. But when I try to compile it I keep getting errors which I cant seem to find soloutions too: Error says <identifier> expected for Line 67 public static void () Assignment brief To write a simple java classMobile that models a mobile phone. Details the information stored about each mobile phone will include • Its type e.g. “Sony ericsson x90” or “Samsung Galaxy S”; • Its screen size in inches; You may assume that this a whole number from the scale 3 to 5 inclusive. • Its memory card capacity in gigabytes You may assume that this a whole number • The name of its present service provider You may assume this is a single line of text. • The type of contract with service provider You may assume this is a single line of text. • Its camera resolution in megapixels; You should not assume that this a whole number; • The percentage of charge left on the phone e.g. a fully charged phone will have a charge of 100. You may assume that this a whole number • Whether the phone has GPS or not. Your class will have fields corresponding to these attributes . Start by opening BlueJ, creating a new project called myMobile which has a classMobile and set up the fields that you need, Next you will need to write a Constructor for the class. Assume that each phone is manufactured by creating an object and specifying its type, its screen size, its memory card capacity, its camera resolution and whether it has GPS or not. Therefore you will need a constructor that allows you to pass arguments to initialise these five attributes. Other fields should be set to appropriate default values. You may assume that a new phone comes fully charged. When the phone is sold to its owner, you will need to set the service provider and type of contract with that provider so you will need mutator methods • setProvider () - - to set service provider. • setContractType - - to set the type of contract These methods will be used when the phones provider is changed. You should also write a mutator method ChargeUp () which simulates fully charging the phone. To obtain information about your mobile object you should write • accessor methods corresponding to four of its fields: • getType () – which returns the type of mobile; • getProvider () – which returns the present service provider; • getContractType () – which returns its type of contract; • getCharge () – which returns its remaining charge. An accessor method to printDetails () to print, to the terminal window, a report about the phone e.g. This mobile phone is a sony Erricsson X90 with Service provider BigAl and type of contract PAYG. At present it has 30% of its battery charge remaining. Check that the new method works correctly by for example, • creating a Mobile object and setting its fields; • calling printDetails () and t=checking the report corresponds to the details you have just given the mobile; • changing the service provider and contract type by calling setprovider () and setContractType (); • calling printDetails () and checking the report now prints out the new details. Challenging excercises • write a mutator methodswitchedOnFor () =which simulates using the phone for a specified period. You may assume the phone loses 1% of its charge for each hour that it is switched on . • write an accessor method checkcharge () whichg checks the phone remaing charge. If this charge has a value less than 25%, then this method returns a string containg the message Be aware that you will soon need to re-charge your phone, otherwise it returns a string your phone charge is sufficient. • Write a method changeProvider () which simulates changing the provider (and presumably also the type of service contract). Finally you may add up to four additional fields, with appropriate methods, that might be required in a more detailed model. above is my assignment that I have, this assignment code I've tried. But when I try to oompile it I keep getting errors which I cant seem to find soloutions too: Error says <identifier> expected for Line 67 public static void () /** * to write a simple java class Mobile that models a mobile phone. * * @author (Lewis Burte-Clarke) * @version (14/10/13) */ public class Mobile { // type of phone private String phonetype; // size of screen in inches private int screensize; // menory card capacity private int memorycardcapacity; // name of present service provider private String serviceprovider; // type of contract with service provider private int typeofcontract; // camera resolution in megapixels private int cameraresolution; // the percentage of charge left on the phone private int checkcharge; // wether the phone has GPS or not private String GPS; // instance variables - replace the example below with your own private int x; // The constructor method public Mobile(String mobilephonetype, int mobilescreensize, int mobilememorycardcapacity,int mobilecameraresolution,String mobileGPS, String newserviceprovider) { this.phonetype = mobilephonetype; this.screensize = mobilescreensize; this.memorycardcapacity = mobilememorycardcapacity; this.cameraresolution = mobilecameraresolution; this.GPS = mobileGPS; // you do not use this ones during instantiation,you can remove them if you do not need or assign them some default values //this.serviceprovider = newserviceprovider; //this.typeofcontract = 12; //this.checkcharge = checkcharge; Mobile samsungPhone = new Mobile("Samsung", "1024", "2", "verizon", "8", "GPS"); 1024 = screensize; 2 = memorycardcapacity; 8 = resolution; GPS = gps; "verizon"=serviceprovider; //typeofcontract = 12; //checkcharge = checkcharge; } // A method to display the state of the object to the screen public void displayMobileDetails() { System.out.println("phonetype: " + phonetype); System.out.println("screensize: " + screensize); System.out.println("memorycardcapacity: " + memorycardcapacity); System.out.println("cameraresolution: " + cameraresolution); System.out.println("GPS: " + GPS); System.out.println("serviceprovider: " + serviceprovider); System.out.println("typeofcontract: " + typeofcontract); } /** * The mymobile class implements an application that * simply displays "new Mobile!" to the standard output. */ public class mymobile { public static void main(String[] args) { System.out.println("new Mobile!"); //Display the string. } } public static void buildPhones(){ Mobile Samsung = new Mobile("Samsung", "3.0", "4gb", "8mega pixels", "GPS"); Mobile Blackberry = new Mobile("Blackberry", "3.0", "4gb", "8mega pixels", "GPS"); Samsung.displayMobileDetails(); Blackberry.displayMobileDetails(); } public static void main(String[] args) { buildPhones(); } } any answers.replies and help would be greatly appreciated as I really lost!

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  • WP7 databinding displays int but not string?

    - by user1794106
    Whenever I test my app.. it binds the data from Note class and displays it if it isn't a string. But for the string variables it wont bind. What am I doing wrong? Inside my main: <Grid x:Name="ContentPanel" Grid.Row="1" Margin="12,0,12,0"> <ListBox x:Name="Listbox" SelectionChanged="listbox_SelectionChanged" ItemsSource="{Binding}"> <ListBox.ItemTemplate> <DataTemplate> <Border Width="800" MinHeight="60"> <StackPanel> <TextBlock x:Name="Title" VerticalAlignment="Center" FontSize="{Binding TextSize}" Text="{Binding Name}"/> <TextBlock x:Name="Date" VerticalAlignment="Center" FontSize="{Binding TextSize}" Text="{Binding Modified}"/> </StackPanel> </Border> </DataTemplate> </ListBox.ItemTemplate> </ListBox> </Grid> </Grid> in code behind: protected override void OnNavigatedTo(System.Windows.Navigation.NavigationEventArgs e) { MessageBox.Show("enters onNav Main"); DataContext = null; DataContext = Settings.NotesList; Settings.CurrentNoteIndex = -1; Listbox.SelectedIndex = -1; if (Settings.NotesList != null) { if (Settings.NotesList.Count == 0) { Notes.Text = "No Notes"; } else { Notes.Text = ""; } } } and public static class Settings { public static ObservableCollection<Note> NotesList; static IsolatedStorageSettings settings; private static int currentNoteIndex; static Settings() { NotesList = new ObservableCollection<Note>(); settings = IsolatedStorageSettings.ApplicationSettings; MessageBox.Show("enters constructor settings"); } notes class: public class Note { public DateTimeOffset Modified { get; set; } public string Title { get; set; } public string Content { get; set; } public int TextSize { get; set; } public Note() { MessageBox.Show("enters Note Constructor"); Modified = DateTimeOffset.Now; Title = "test"; Content = "test"; TextSize = 32; } }

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  • Trigger function on deserialization

    - by Tom Savage
    I have a class with a number of fields which are normally calculated in the constructor from other data in the class. They are not serialized to XML because any changes to the rest of the data will likely require their recalculation. Is there a way I can set up a function call to be triggered on deserialization?

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  • Java reflection framework and security

    - by Jijoy
    Hi , Assume I have a singleton class in an external lib to my application. But still I can create instances of that particular class using reflection. Like this Class clas = Class.forName(Private.class.getName()); for(Constructor c : clas.getDeclaredConstructors()){ c.setAccessible(true); Private p = (Private) c.newInstance(); System.out.println(p); } How can I restrict this ? . Thanks J

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  • Qt gstreamer problem

    - by ZolaKt
    Ptterb can you post your full code please? I copied your code. Added fvidscale_cap to pipeline, with: self.player.add(self.source, self.scaler, self.fvidscale_cap, self.sink) gst.element_link_many(self.source,self.scaler, self.fvidscale_cap, self.sink) From the main program I create a new QWidget, and pass its winId() to Vid constructor. The widget start loading, but crashes. The output says: should be playing Segmentation fault

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  • Extend Javascript Date Object

    - by jAndy
    Hi Folks, I'm curious what would be the best practice to extend the Date constructor. The problem I'm facing is, that the Internet Explorer (< 7+8) can't parse a date like new Date('2010-05-11'); I have to admit that this is not a standard method to parse, anyways FireFox and Chrome perform well on that kind of date string. Now I'm wondering, should I just split/parse/rebuild the string before calling new Date() or is there a more elegant solution ?

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  • XNA and Ninject: Syntax for dependency arguments?

    - by Rosarch
    I have a class with a public constructor: public MasterEngine(IInputReader inputReader) { this.inputReader = inputReader; graphicsDeviceManager = new GraphicsDeviceManager(this); Components.Add(new GamerServicesComponent(this)); } How can I inject dependencies like graphicsDeviceManager and new GamerServicesComponent while still supplying the argument this?

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  • How deep are your unit tests?

    - by John Nolan
    The thing I've found about TDD is that its takes time to get your tests set up and being naturally lazy I always want to write as little code as possible. The first thing I seem do is test my constructor has set all the properties but is this overkill? My question is to what level of granularity do you write you unit tests at? ..and is there a case of testing too much?

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  • Proper exceptions to use for nulls

    - by user200295
    In the following example we have two different exceptions we want to communicate. //constructor public Main(string arg){ if(arg==null) throw new ArgumentNullException("arg"); Thing foo=GetFoo(arg); if(foo==null) throw new NullReferenceException("foo is null"); } Is this the proper approach for both exception types?

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  • __proto__ of a function

    - by alter
    if I have a class called Person. var Person = function(fname, lname){ this.fname = fname; this.lname = lname; } Person.prototype.mname = "Test"; var p = new Person('Alice','Bob'); Now, p.proto refers to prototype of Person but, when I try to do Person.proto , it points to function(), and Person.constructor points to Function(). can some1 explain what is the difference between function() and Function() and why prototype of a Function() class is a function()

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  • javax.activation.DataSource size question

    - by folone
    How do I get the amount of physical memory, consumed by the DataSource (specifically — ByteArrayDataSource)? I use ByteArrayDataSource (byte[] bytes, String type) constructor, where I get bytes like this: String str = "test"; byte[] bytes = str.getBytes(); Would that be str.length() in bytes? Any other ideas?

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  • How to print structures in PLT Scheme so as to display their fields?

    - by tkf
    I would like code like this: (define-struct thing (a b c)) (define th (make-thing 1 2 3)) to print something like this: (make-thing 1 2 3) when I type "th" into either the DrScheme or MzScheme repl. I am using the language "pretty big" in DrScheme with output style set to "constructor". This is what I get in DrScheme: (make-thing ...) (i literally get the three dots) In MzScheme: #<thing>

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  • CursorLoader, get URI for local database

    - by user1681358
    I'm a newbie android programmer and I recently followed a tutorial which shows how to create a local SQLite database by using SQLiteDatabase.rawQuery to return a Cursor. I would like to modify my app to use CursorLoader which is apparently a better way to access the database. My problem is the CursorLoader constructor expects a URI to be given. Do I just input "file:///[path to db]"? Seems a bit messy.

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  • NCommon - changes in 1.1

    - by Innogetics
    I updated my NCommon version to 1.1. It looks like there are breaking changes. What happened to: the Store container class? the NHRepository constructor that accepts an ISession? How should I modify my code to address these changes?

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  • Are reference attributes destroyed when class is destroyed in C++?

    - by Genba
    Suppose I have a C++ class with an attribute that is a reference: class ClassB { ClassA &ref; public: ClassB(ClassA &_ref); } Of course, the constructor is defined this way: ClassB::ClassB(ClassA &_ref) : ref(_ref) { /* ... */ } My question is: When an instance of class 'ClassB' is destroyed, is the object referenced by 'ClassB::ref' also destroyed?

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  • .NET: Start a thread as suspended

    - by Ikaso
    In unmanaged code you can create a thread in suspended state. In .NET Framework I can't find this option. Is it because the Thread constructor puts the thread in a suspended state? Is there other reasons why this is not supported?

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  • IoC Dependancy injection into Custom HTTP Module - how? (ASP.NET)

    - by Sosh
    Hi, I have a custom HTTP Module. I would like to inject the logger using my IoC framework, so I can log errors in the module. However, of course I don't get a constructor, so can't inject it into that. What's the best way to go about this? If you need the specific IoC container - I'm currently using Windsor, but may soon move to AutoFac. Thanks

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  • c# 3.5 class List<int> class initialisation

    - by josephj1989
    I can initialize a List like new List{1,2,3,4,5}; However List does not have a constructor which accepts a single parameter. So I tried to run this through the debugger and it seems to be calling the Add method. So how does the compiler know which method to invoke to add each individual element. This may be a silly question but I am a bit confused. Thanks

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  • How can I pass a C++ member function to a C API as a parameter

    - by michael
    Hi, In my C++ program, I need to call this c API: GConn* gnet_conn_new (const gchar *hostname, gint port, GConnFunc func); where GConnFunc is defined as: void (*GConnFunc) (GConn *conn); My question is if I have a C++ class and have a member function like Class A { public: A(); void my_func (GConn* conn); } In my A::A() Constructor, how can I pass this-myfunc to gnet_conn_new as the GConnFunc parameter? Thank you.

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