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  • What does Ruby have that Python doesn't, and vice versa?

    - by Lennart Regebro
    There is a lot of discussions of Python vs Ruby, and I all find them completely unhelpful, because they all turn around why feature X sucks in language Y, or that claim language Y doesn't have X, although in fact it does. I also know exactly why I prefer Python, but that's also subjective, and wouldn't help anybody choosing, as they might not have the same tastes in development as I do. It would therefore be interesting to list the differences, objectively. So no "Python's lambdas sucks". Instead explain what Ruby's lambdas can do that Python's can't. No subjectivity. Example code is good! Don't have several differences in one answer, please. And vote up the ones you know are correct, and down those you know are incorrect (or are subjective). Also, differences in syntax is not interesting. We know Python does with indentation what Ruby does with brackets and ends, and that @ is called self in Python. UPDATE: This is now a community wiki, so we can add the big differences here. Ruby has a class reference in the class body In Ruby you have a reference to the class (self) already in the class body. In Python you don't have a reference to the class until after the class construction is finished. An example: class Kaka puts self end self in this case is the class, and this code would print out "Kaka". There is no way to print out the class name or in other ways access the class from the class definition body in Python. All classes are mutable in Ruby This lets you develop extensions to core classes. Here's an example of a rails extension: class String def starts_with?(other) head = self[0, other.length] head == other end end Ruby has Perl-like scripting features Ruby has first class regexps, $-variables, the awk/perl line by line input loop and other features that make it more suited to writing small shell scripts that munge text files or act as glue code for other programs. Ruby has first class continuations Thanks to the callcc statement. In Python you can create continuations by various techniques, but there is no support built in to the language. Ruby has blocks With the "do" statement you can create a multi-line anonymous function in Ruby, which will be passed in as an argument into the method in front of do, and called from there. In Python you would instead do this either by passing a method or with generators. Ruby: amethod { |here| many=lines+of+code goes(here) } Python: def function(here): many=lines+of+code goes(here) amethod(function) Interestingly, the convenience statement in Ruby for calling a block is called "yield", which in Python will create a generator. Ruby: def themethod yield 5 end themethod do |foo| puts foo end Python: def themethod(): yield 5 for foo in themethod: print foo Although the principles are different, the result is strikingly similar. Python has built-in generators (which are used like Ruby blocks, as noted above) Python has support for generators in the language. In Ruby you could use the generator module that uses continuations to create a generator from a block. Or, you could just use a block/proc/lambda! Moreover, in Ruby 1.9 Fibers are, and can be used as, generators. docs.python.org has this generator example: def reverse(data): for index in range(len(data)-1, -1, -1): yield data[index] Contrast this with the above block examples. Python has flexible name space handling In Ruby, when you import a file with require, all the things defined in that file will end up in your global namespace. This causes namespace pollution. The solution to that is Rubys modules. But if you create a namespace with a module, then you have to use that namespace to access the contained classes. In Python, the file is a module, and you can import its contained names with from themodule import *, thereby polluting the namespace if you want. But you can also import just selected names with from themodule import aname, another or you can simply import themodule and then access the names with themodule.aname. If you want more levels in your namespace you can have packages, which are directories with modules and an __init__.py file. Python has docstrings Docstrings are strings that are attached to modules, functions and methods and can be introspected at runtime. This helps for creating such things as the help command and automatic documentation. def frobnicate(bar): """frobnicate takes a bar and frobnicates it >>> bar = Bar() >>> bar.is_frobnicated() False >>> frobnicate(bar) >>> bar.is_frobnicated() True """ Python has more libraries Python has a vast amount of available modules and bindings for libraries. Python has multiple inheritance Ruby does not ("on purpose" -- see Ruby's website, see here how it's done in Ruby). It does reuse the module concept as a sort of abstract classes. Python has list/dict comprehensions Python: res = [x*x for x in range(1, 10)] Ruby: res = (0..9).map { |x| x * x } Python: >>> (x*x for x in range(10)) <generator object <genexpr> at 0xb7c1ccd4> >>> list(_) [0, 1, 4, 9, 16, 25, 36, 49, 64, 81] Ruby: p = proc { |x| x * x } (0..9).map(&p) Python: >>> {x:str(y*y) for x,y in {1:2, 3:4}.items()} {1: '4', 3: '16'} Ruby: >> Hash[{1=>2, 3=>4}.map{|x,y| [x,(y*y).to_s]}] => {1=>"4", 3=>"16"} Python has decorators Things similar to decorators can be created in Ruby, and it can also be argued that they aren't as necessary as in Python.

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  • What should I call the operation that limit a string's length?

    - by egarcia
    This is a language-agnostic question - unless you count English as a language. I've got this list of items which can have very long names. For aesthetic purposes, these names must be made shorter in some cases, adding dots (...) to indicate that the name is longer. So for example, if article.name returns this: lorem ipsum dolor sit amet I'd like to get this other output. lorem ipsum dolor ... I can program this quite easily. My question is: how should I call that shortening operation? I mean the name, not the implementation. Is there a standard English name for it?

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  • Avoiding circular project/assembly references in Visual Studio with statically typed dependency conf

    - by svnpttrssn
    First, I want to say that I am not interested in debating about any non-helpful "answers" to my question, with suggestions to putting everything in one assembly, i.e. there is no need for anyone to provide webpages such as the page titled with "Separate Assemblies != Loose Coupling". Now, my question is if it somehow (maybe with some Visual Studio configuration to allow for circular project dependencies?) is possible to use one project/assembly (I am here calling it the "ServiceLocator" assembly) for retrieving concrete implementation classes, (e.g. with StructureMap) which can be referred to from other projects, while it of course is also necessary for the the ServiceLocator itself to refer to other projects with the interfaces and the implementations ? Visual Studio project example, illustrating the kind of dependency structure I am talking about: http://img10.imageshack.us/img10/8838/testingdependencyinject.png Please note in the above picture, the problem is how to let the classes in "ApplicationLayerServiceImplementations" retrieve and instantiate classes that implement the interfaces in "DomainLayerServiceInterfaces". The goal is here to not refer directly to the classes in "DomainLayerServiceImplementations", but rather to try using the project "ServiceLocator" to retrieve such classes, but then the circular dependency problem occurrs... For example, a "UserInterfaceLayer" project/assembly might contain this kind of code: ContainerBootstrapper.BootstrapStructureMap(); // located in "ServiceLocator" project/assembly MyDomainLayerInterface myDomainLayerInterface = ObjectFactory.GetInstance<MyDomainLayerInterface>(); // refering to project/assembly "DomainLayerServiceInterfaces" myDomainLayerInterface.MyDomainLayerMethod(); MyApplicationLayerInterface myApplicationLayerInterface = ObjectFactory.GetInstance<MyApplicationLayerInterface>(); // refering to project/assembly "ApplicationLayerServiceInterfaces" myApplicationLayerInterface.MyApplicationLayerMethod(); The above code do not refer to the implementation projects/assemblies ApplicationLayerServiceImplementations and DomainLayerServiceImplementations, which contain this kind of code: public class MyApplicationLayerImplementation : MyApplicationLayerInterface and public class MyDomainLayerImplementation : MyDomainLayerInterface The "ServiceLocator" project/assembly might contain this code: using ApplicationLayerServiceImplementations; using ApplicationLayerServiceInterfaces; using DomainLayerServiceImplementations; using DomainLayerServiceInterfaces; using StructureMap; namespace ServiceLocator { public static class ContainerBootstrapper { public static void BootstrapStructureMap() { ObjectFactory.Initialize(x => { // The two interfaces and the two implementations below are located in four different Visual Studio projects x.ForRequestedType<MyDomainLayerInterface>().TheDefaultIsConcreteType<MyDomainLayerImplementation>(); x.ForRequestedType<MyApplicationLayerInterface>().TheDefaultIsConcreteType<MyApplicationLayerImplementation>(); }); } } } So far, no problem, but the problem occurs when I want to let the class "MyApplicationLayerImplementation" in the project/assembly "ApplicationLayerServiceImplementations" use the "ServiceLocator" project/assembly for retrieving an implementation of "MyDomainLayerInterface". When I try to do that, i.e. add a reference from "MyApplicationLayerImplementation" to "ServiceLocator", then Visual Studio complains about circular dependencies between projects. Is there any nice solution to this problem, which does not imply using refactoring-unfriendly string based xml-configuration which breaks whenever an interface or class or its namespace is renamed ? / Sven

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  • Constructor in a Interface?

    - by Sebi
    I know its not possible to define a constructor in a interface. But im wondering why, because i think i could be very useful. So you could be sure that some fields in a class are defined for every implementaiton of this interface. For example consider the following message class: public class MyMessage { public MyMessage(String receiver) { this.receiver = receiver; } private String receiver; public void send() { //some implementation for sending the mssage to the receiver } } If a define a Interface for this class so that i can have more classes which implement the message interface, i can only define the send method and not the constructor. So how can i assure that every implementation of this class really has an receiver setted? If i use a method like setReceiver(String receiver) i can't be sure that this method is really called. In the constructor i could assure it.

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  • "Use of undefined constant CURLOPT_PROTOCOLS and CURLPROTO_HTTP" but it works?

    - by Dave
    Hi on our dev environment we have show all errors, warnings and notices. I'm getting this: Notice: Use of undefined constant CURLOPT_PROTOCOLS - assumed 'CURLOPT_PROTOCOLS' in C:\notion\implementation\development\asterix\library\ExternalLibs\panda.php on line 69 Notice: Use of undefined constant CURLPROTO_HTTP - assumed 'CURLPROTO_HTTP' in C:\notion\implementation\development\asterix\library\ExternalLibs\panda.php on line 69 The code on line 69: curl_setopt($curl, CURLOPT_PROTOCOLS, CURLPROTO_HTTP); But the CURL code works, it goes off to the other server and retrieves whats necessary. What do these notices mean? Thanks very much.

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  • groovy call private method in Java super class

    - by Jeff Storey
    I have an abstract Java class MyAbstractClass with a private method. There is a concrete implementation MyConcreteClass. public class MyAbstractClass { private void somePrivateMethod(); } public class MyConcreteClass extends MyAbstractClass { // implementation details } In my groovy test class I have class MyAbstractClassTest { void myTestMethod() { MyAbstractClass mac = new MyConcreteClass() mac.somePrivateMethod() } } I get an error that there is no such method signature for somePrivateMethod. I know groovy can call private methods but I'm guessing the problem is that the private method is in the super class, not MyConcreteClass. Is there a way to invoke a private method in the super class like this (other than using something like PrivateAccessor)? thanks Jeff

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  • how to implement IOC without a global static service (non-service locator solution)?

    - by Michel
    Hi, we want to use Unity for IOC. All i've seen is the implementation that there is one global static service which holds a reference to the Unity container, which registers all interface/class combinations and every class asks that object: give me an implementation for Ithis or IThat. Frequently i see a response that this pattern is not good because it leads to a dependency from ALL classes to this service. But what i don't see often, is: what is the alternative way? Michel EDIT: found out that the global static service is called the service locator, added that to the title.

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  • Google Web Toolkit Deferred Binding Issue

    - by snctln
    I developed a web app using GWT about 2 years ago, since then the application has evolved. In its current state it relies on fetching a single XML file and parsing the information from it. Overall this works great. A requirement of this app is that it needs to be able to be ran from the filesystem (file:///..) as well as the traditional model of running from a webserver (http://...) Fetching this file from a webserver works exactly as expected using a RequestBuilder object. When running the app from the filesystem Firefox, Opera, Safari, and Chrome all behave as expected. When running the app from the filesystem using IE7 or IE8 the RequestBuilder.send() call fails, the information about the error suggests that there is a problem accessing the file due to violating the same origin policy. The app worked as expected in IE6 but not in IE7 or IE8. So I looked at the source code of RequestBuilder.java and saw that the actual request was being executed with an XMLHttpRequest GWT object. So I looked at the source code for XMLHttpRequest.java and found out some information. Here is the code (starts at line 83 in XMLHttpRequest.java) public static native XMLHttpRequest create() /*-{ if ($wnd.XMLHttpRequest) { return new XMLHttpRequest(); } else { try { return new ActiveXObject('MSXML2.XMLHTTP.3.0'); } catch (e) { return new ActiveXObject("Microsoft.XMLHTTP"); } } }-*/; So basically if an XMLHttpRequest cannot be created (like in IE6 because it is not available) an ActiveXObject is used instead. I read up a little bit more on the IE implementation of XMLHttpRequest, and it appears that it is only supported for interacting with files on a webserver. I found a setting in IE8 (Tools-Internet Options-Advanced-Security-Enable native XMLHTTP support), when I uncheck this box my app works. I assume this is because I am more of less telling IE to not use their implementation of XmlHttpRequest, so GWT just uses an ActiveXObject because it doesn't think the native XmlHttpRequest is available. This fixes the problem, but is hardly a long term solution. I can currently catch a failed send request and verify that it was trying to fetch the XML file from the filesystem using normal GWT. What I would like to do in this case is catch the IE7 and IE8 case and have them use a ActiveXObject instead of a native XmlHttpRequest object. There was a posting on the GWT google group that had a supposed solution for this problem (link). Looking at it I can tell that it was created for an older version of GWT. I am using the latest release and think that this is more or less what I would like to do (use GWT deferred binding to detect a specific browser type and run my own implementation of XMLHttpRequest.java in place of the built in GWT implementation). Here is the code that I am trying to use package com.mycompany.myapp.client; import com.google.gwt.xhr.client.XMLHttpRequest; public class XMLHttpRequestIE7or8 extends XMLHttpRequest { // commented out the "override" so that eclipse and the ant build script don't throw errors //@Override public static native XMLHttpRequest create() /*-{ try { return new ActiveXObject('MSXML2.XMLHTTP.3.0'); } catch (e) { return new ActiveXObject("Microsoft.XMLHTTP"); } }-*/; // have an empty protected constructor so the ant build script doesn't throw errors // the actual XMLHttpRequest constructor is empty as well so this shouldn't cause any problems protected XMLHttpRequestIE7or8() { } }; And here are the lines that I added to my module xml <replace-with class="com.mycompany.myapp.client.XMLHttpRequestIE7or8"> <when-type-is class="com.google.gwt.xhr.client.XMLHttpRequest"/> <any> <when-property-is name="user.agent" value="ie7" /> <when-property-is name="user.agent" value="ie8" /> </any> </replace-with> From what I can tell this should work, but my code never runs. Does anyone have any idea of what I am doing wrong? Should I not do this via deferred binding and just use native javascript when I catch the fail case instead? Is there a different way of approaching this problem that I have not mentioned? All replies are welcome.

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  • Webserver parsing chrome input from post request

    - by ravenspoint
    I am developing a small embedded web server. I want to add parsing of post requests, but I am having a problem with input password fields from Chrome. Firefox and IE work perfectly. The HTML: <form action=start.webem method=post> <input value="START" type=submit /><!--#webem start --> <p>Password: <input TYPE=PASSWORD name=yourname AUTOCOMPLETE=OFF /><br> </form> From Firefox I get POST /stop.webem HTTP/1.1 Host: 127.0.0.1:8080 User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.9.1.9) Gecko/20100315 Firefox/3.5.9 (.NET CLR 3.5.30729) Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8 Accept-Language: en-us,en;q=0.5 Accept-Encoding: gzip,deflate Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.7 Keep-Alive: 300 Connection: keep-alive Referer: http://127.0.0.1:8080/ Content-Type: application/x-www-form-urlencoded Content-Length: 13 yourname=test However from Chrome, about 90% of the time, the yourname=test is missing POST /start.webem HTTP/1.1 Host: 127.0.0.1:8080 Connection: keep-alive User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US) AppleWebKit/532.5 (KHTML, like Gecko) Chrome/4.1.249.1045 Safari/532.5 Referer: http://127.0.0.1:8080/ Content-Length: 13 Cache-Control: max-age=0 Origin: http://127.0.0.1:8080 Content-Type: application/x-www-form-urlencoded Accept: application/xml,application/xhtml+xml,text/html;q=0.9,text/plain;q=0.8,image/png,*/*;q=0.5 Accept-Encoding: gzip,deflate,sdch Accept-Language: en-US,en;q=0.8 Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.3 Though, occasionally it does work!!! POST /start.webem HTTP/1.1 Host: 127.0.0.1:8080 Connection: keep-alive User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US) AppleWebKit/532.5 (KHTML, like Gecko) Chrome/4.1.249.1045 Safari/532.5 Referer: http://127.0.0.1:8080/start.webem Content-Length: 13 Cache-Control: max-age=0 Origin: http://127.0.0.1:8080 Content-Type: application/x-www-form-urlencoded Accept: application/xml,application/xhtml+xml,text/html;q=0.9,text/plain;q=0.8,image/png,*/*;q=0.5 Accept-Encoding: gzip,deflate,sdch Accept-Language: en-US,en;q=0.8 Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.3 yourname=test I cannot find what causes it to work sometimes.

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  • User Interface functionality modelling languages?

    - by naugtur
    I am looking for a UI functionality modelling language (UML-alike "thing", but for user interfaces) that is already accepted and maybe has its design patterns and handles the problem better than state or activity diagram. (If there is no such thing I'm planning to develop that BTW :)) This question came to mind as a result of a discovery that UML and its diagrams fails at describing complicated UI functionality with event-driven flow of execution (ie. javascript/jQuery big projects) EDIT: I've been thinking of using BPMN but It was not created for this purpose. EDIT2: See this community topic of mine - I decided to start developing said language.

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  • Cannot instantiate abstract class or interface : problem while persisting

    - by sammy
    i have a class campaign that maintains a list of AdGroupInterfaces. im going to persist its implementation @Entity @Table(name = "campaigns") public class Campaign implements Serializable,Comparable<Object>,CampaignInterface { private static final long serialVersionUID = 1L; @Id @GeneratedValue(strategy = GenerationType.IDENTITY) private Long id; @OneToMany ( cascade = {CascadeType.ALL}, fetch = FetchType.EAGER, targetEntity=AdGroupInterface.class ) @org.hibernate.annotations.Cascade( value = org.hibernate.annotations.CascadeType.DELETE_ORPHAN ) @org.hibernate.annotations.IndexColumn(name = "CHOICE_POSITION") private List<AdGroupInterface> AdGroup; public Campaign() { super(); } public List<AdGroupInterface> getAdGroup() { return AdGroup; } public void setAdGroup(List<AdGroupInterface> adGroup) { AdGroup = adGroup; } public void set1AdGroup(AdGroupInterface adGroup) { if(AdGroup==null) AdGroup=new LinkedList<AdGroupInterface>(); AdGroup.add(adGroup); } } AdGroupInterface's implementation is AdGroups. when i add an adgroup to the list in campaign, campaign c; c.getAdGroupList().add(new AdGroups()), etc and save campaign it says"Cannot instantiate abstract class or interface :" AdGroupInterface its not recognizing the implementation just before persisting... Whereas Persisting adGroups separately works. when it is a member of another entity, it doesnt get persisted. import java.io.Serializable; import java.util.List; import javax.persistence.*; @Entity @DiscriminatorValue("1") @Table(name = "AdGroups") public class AdGroups implements Serializable,Comparable,AdGroupInterface{ /** * */ private static final long serialVersionUID = 1L; private Long Id; private String Name; private CampaignInterface Campaign; private MonetaryValue DefaultBid; public AdGroups(){ super(); } public AdGroups( String name, CampaignInterface campaign) { super(); this.Campaign=new Campaign(); Name = name; this.Campaign = campaign; DefaultBid = defaultBid; AdList=adList; } @Id @GeneratedValue(strategy = GenerationType.IDENTITY) @Column(name="AdGroup_Id") public Long getId() { return Id; } public void setId(Long id) { Id = id; } @Column(name="AdGroup_Name") public String getName() { return Name; } public void setName(String name) { Name = name; } @ManyToOne @JoinColumn (name="Cam_ID", nullable = true,insertable = false) public CampaignInterface getCampaign() { return Campaign; } public void setCampaign(CampaignInterface campaign) { this.Campaign = campaign; } } what am i missing?? please look into it ...

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  • What is the accepted pattern for WPF commanding in MVVM?

    - by Robert S.
    I'm working on a WPF app and I understand the command pattern pretty well, but I've found that there are several different implementations of the command pattern for MVVM. There's Josh Smith's implementation in his WPF sample app, the DelegateCommand from Prism, and the CommandBindings implementation. My question is, what is the generally accepted best practice for using commands with MVVM? My application uses Prism so DelegateCommand is available to us. The devs on my team are arguing about which approach is "best." Some don't like the numerous .cs files generated for each command, others prefer that everything be wired up via CommandBindings. I'm at a loss. Can anyone shed some light?

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  • Does C99 guarantee that arrays are contiguous ?

    - by kriss
    Following an hot comment thread in another question, I came to debate of what is and what is not defined in C99 standard about C arrays. Basically when I define a 2D array like int a[5][5], does the standard C99 garantee or not that it will be a contiguous block of ints, can I cast it to (int *)a and be sure I will have a valid 1D array of 25 ints. As I understand the standard the above property is implicit in the sizeof definition and in pointer arithmetic, but others seems to disagree and says casting to (int*) the above structure give an undefined behavior (even if they agree that all existing implementations actually allocate contiguous values). More specifically, if we think an implementation that would instrument arrays to check array boundaries for all dimensions and return some kind of error when accessing 1D array, or does not give correct access to elements above 1st row. Could such implementation be standard compilant ? And in this case what parts of the C99 standard are relevant.

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  • Python KMeans clustering words

    - by sadawd
    Dear Everyone I am interested to perform kmeans clustering on a list of words with the distance measure being Leveshtein. 1) I know there are a lot of frameworks out there, including scipy and orange that has a kmeans implementation. However they all require some sort of vector as the data which doesn't really fit me. 2) I need a good clustering implementation. I looked at python-clustering and realize that it doesn't a) return the sum of all the distance to each centroid, and b) it doesn't have any sort of iteration limit or cut off which ensures the quality of the clustering. python-clustering and the clustering algorithm on daniweb doesn't really work for me. Can someone find me a good lib? Google hasn't been my friend

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  • How are you using IronPython?

    - by Will Dean
    I'm keen to drink some modern dynamic language koolaid, so I've believed all the stuff on Michael Foord's blog and podcasts, I've bought his book (and read some of it), and I added an embedded IPy runtime to a large existing app a year or so ago (though that was for someone else and I didn't really use it myself). Now I need to do some fairly simple code generation stuff, where I'm going to call a few methods on a few .net objects (custom, C#-authored objects), create a few strings, write some files, etc. The experience of trying this leaves me feeling like the little boy who thinks he's the only one who can see that The Emperor has no clothes on. If you're using IronPython, I'd really appreciate knowing how you deal with the following aspects of it: Code editing - do you use the .NET framework without Intellisense? Refactoring - I know a load of 'refactoring' is about working around language-related busywork, so if Python is sufficiently lightweight then we won't need that, But things like renames seem to me to be essential to iteratively developing quality code regardless of language. Crippling startup time - One of the things which is supposed to be good about interpreted languages is the lack of compile time leading to fast interactive development. Unfortunately I can compile a C# application and launch it quicker than IPy can start up. Interactive hacking - the IPy console/repl is supposed to be good for this, but I haven't found a good way to take the code you've interactively arrived at and persist it into a file - cut and paste from the console is fairly miserable. And the console seems to hold references to .NET assemblies you've imported, so you have to quit it and restart it if you're working on the C# stuff as well. Hacking on C# in something like LinqPad seems a much faster and easier way to try things out (and has proper Intellisense). Do you use the console? Debugging - what's the story here? I know someone on the IPy team is working on a command-line hobby-project, but let's just say I'm not immediately attracted to a command line debugger. I don't really need a debugger from little Python scripts, but I would if I were to use IPy for scripting unit tests, for example. Unit testing - I can see that dynamic languages could be great for this, but is there any IDE test-runner integration (like for Resharper, etc). The Foord book has a chapter about this, which I'll admit I have not yet read properly, but it does seem to involve driving a console-mode test-runner from the command prompt, which feels to be an enormous step back from using an integrated test runner like TestDriven.net or Resharper. I really want to believe in this stuff, so I am still working on the assumption that I've missed something. I would really like to know how other people are dealing with IPy, particularly if they're doing it in a way which doesn't feel like we've just lost 15 years'-worth of tool development.

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  • .Net Dynamically Load DLL

    - by hermiod
    I am trying to write some code that will allow me to dynamically load DLLs into my application, depending on an application setting. The idea is that the database to be accessed is set in the application settings and then this loads the appropriate DLL and assigns it to an instance of an interface for my application to access. This is my code at the moment: Dim SQLDataSource As ICRDataLayer Dim ass As Assembly = Assembly. _ LoadFrom("M:\MyProgs\WebService\DynamicAssemblyLoading\SQLServer\bin\Debug\SQLServer.dll") Dim obj As Object = ass.CreateInstance(GetType(ICRDataLayer).ToString, True) SQLDataSource = DirectCast(obj, ICRDataLayer) MsgBox(SQLDataSource.ModuleName & vbNewLine & SQLDataSource.ModuleDescription) I have my interface (ICRDataLayer) and the SQLServer.dll contains an implementation of this interface. I just want to load the assembly and assign it to the SQLDataSource object. The above code just doesn't work. There are no exceptions thrown, even the Msgbox doesn't appear. I would've expected at least the messagebox appearing with nothing in it, but even this doesn't happen! Is there a way to determine if the loaded assembly implements a specific interface. I tried the below but this also doesn't seem to do anything! For Each loadedType As Type In ass.GetTypes If GetType(ICRDataLayer).IsAssignableFrom(loadedType) Then Dim obj1 As Object = ass.CreateInstance(GetType(ICRDataLayer).ToString, True) SQLDataSource = DirectCast(obj1, ICRDataLayer) End If Next EDIT: New code from Vlad's examples: Module CRDataLayerFactory Sub New() End Sub ' class name is a contract, ' should be the same for all plugins Private Function Create() As ICRDataLayer Return New SQLServer() End Function End Module Above is Module in each DLL, converted from Vlad's C# example. Below is my code to bring in the DLL: Dim SQLDataSource As ICRDataLayer Dim ass As Assembly = Assembly. _ LoadFrom("M:\MyProgs\WebService\DynamicAssemblyLoading\SQLServer\bin\Debug\SQLServer.dll") Dim factory As Object = ass.CreateInstance("CRDataLayerFactory", True) Dim t As Type = factory.GetType Dim method As MethodInfo = t.GetMethod("Create") Dim obj As Object = method.Invoke(factory, Nothing) SQLDataSource = DirectCast(obj, ICRDataLayer) EDIT: Implementation based on Paul Kohler's code Dim file As String For Each file In Directory.GetFiles(baseDir, searchPattern, SearchOption.TopDirectoryOnly) Dim assemblyType As System.Type For Each assemblyType In Assembly.LoadFrom(file).GetTypes Dim s As System.Type() = assemblyType.GetInterfaces For Each ty As System.Type In s If ty.Name.Contains("ICRDataLayer") Then MsgBox(ty.Name) plugin = DirectCast(Activator.CreateInstance(assemblyType), ICRDataLayer) MessageBox.Show(plugin.ModuleName) End If Next I get the following error with this code: Unable to cast object of type 'SQLServer.CRDataSource.SQLServer' to type 'DynamicAssemblyLoading.ICRDataLayer'. The actual DLL is in a different project called SQLServer in the same solution as my implementation code. CRDataSource is a namespace and SQLServer is the actual class name of the DLL. The SQLServer class implements ICRDataLayer, so I don't understand why it wouldn't be able to cast it. Is the naming significant here, I wouldn't have thought it would be.

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  • Buy or Build for web deployment?

    - by Cannonade
    I have been evaluating the wide range of installation and web deployment solutions available for Windows applications. I will just clarify here (without too much detail, these tools have been covered in other questions) my understanding of the options: NSIS - Free tool that generates setup executables. Small binary. Specialized, sometimes obtuse, scripting language. Inno Setup - Free tools for setup executables. Various binary compression schemes. Pascal scripting engine. WIX - Free toolset to generate MSI binaries. XML definitions language. WIX ClickThrough - Additional tools for packaging, web download and auto update detection (now part of WIX core). InstallShield - Commercial development environment for installation packaging. Generates MSI binaries. C-like InstallScript language. Wise - Commercial development environment for installation packaging. Generates MSI binaries. ClickOnce - Visual Studio supported framework for publishing applications to a webserver, with automatic detection of updates. No support for custom installation requirements (INI files, registry etc ...). Packages setup as an MSI binary. Install Aware - Commercial development environment for installation. Generates MSI binaries. Automatic Update framwork (Web Update). If I have missed any, please let me know. And found some useful discussions of these technologies on StackOverflow: Best Simple Install System Best choice for Windows installers Alternatives to ClickOnce I have worked with a few of these solutions, as well as a handful of proprietary internal installation solutions. They are mostly concerned with packing installations and providing a framework for developers to access the run time environment. With the growing requirement for web deployment and automatic software updates, I expected to find more of a consensus among developers on a framework for web delivery of software and subsequent updates, I haven't really found that consensus. There are certainly solutions available (ClickOnce, ClickThrough, InstallShield Update Service), but they each have considerable limitations (please correct me if I mis-represent any of these). I would be interested in a framework that provided some of the following: Third party hosting/management of updates. Access to client environment (INI files, registry, etc..). User registration/activation. Feedback/Error reporting This is leaving me with the strong impression that the best way to approach the web deployment problem is through a custom built proprietary solution (possibly leveraging existing installer packaging). I have seen this sort of solution work well for a number of successful applications: FileZilla - HTTP request to update.filezilla-project.org to check for updates, downloads an NSIS binary (I think) and then shuts down to run the install.

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  • Does different iVar name change retain count when used with property

    - by russell
    Here is 2 code snapshot- Class A:NSObject { NSMutableArray *a; } @property (retain) NSMutableArray *a; @implementation @synthesize a; -(id)init { if(self=[super init]) { a=[[NSMutableArray alloc] init]; } } @end Class A:NSObject { NSMutableArray *_a; } @property (retain) NSMutableArray *a; @implementation @synthesize a=_a; -(id)init { if(self=[super init]) { _a=[[NSMutableArray alloc] init]; } } @end Now what i need to know, is in both code instance variable assigned value directly rather than using accessor and retain count is 1? Or there is difference between them. Thanks. And one more things, apple recommended not to use accessor in init/dealloc, but at the same time ask not to directly set iVar. So what is the best way to assign value of ivar in init()??

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  • difference in logging mechanism: API and application(python)

    - by zubin71
    I am currently writing an API and an application which uses the API. I have gotten suggestions from people stating that I should perform logging using handlers in the application and use a "logger" object for logging from the API. In light of the advice I received above, is the following implementation correct? class test: def __init__(self, verbose): self.logger = logging.getLogger("test") self.logger.setLevel(verbose) def do_something(self): # do something self.logger.log("something") # by doing this i get the error message "No handlers could be found for logger "test" The implementation i had in mind was as follows: #!/usr/bin/python """ .... .... create a logger with a handler .... .... """ myobject = test() try: myobject.do_something() except SomeError: logger.log("cant do something") Id like to get my basics strong, id be grateful for any help and suggestions for code you might recommend I look up. Thnkx!

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  • What is `objc_msgSend_fixup`, exactly?

    - by Luis Antonio Botelho O. Leite
    I'm messing around with the Objective-C runtime, trying to compile objective-c code without linking it against libobjc, and I'm having some segmentation fault problems with a program, so I generated an assembly file from it. I think it's not necessary to show the whole assembly file. At some point of my main function, I've got the following line (which, by the way, is the line after which I get the seg fault): callq *l_objc_msgSend_fixup_alloc and here is the definition for l_objc_msgSend_fixup_alloc: .hidden l_objc_msgSend_fixup_alloc # @"\01l_objc_msgSend_fixup_alloc" .type l_objc_msgSend_fixup_alloc,@object .section "__DATA, __objc_msgrefs, coalesced","aw",@progbits .weak l_objc_msgSend_fixup_alloc .align 16 l_objc_msgSend_fixup_alloc: .quad objc_msgSend_fixup .quad L_OBJC_METH_VAR_NAME_ .size l_objc_msgSend_fixup_alloc, 16 I've reimplemented objc_msgSend_fixup as a function (id objc_msgSend_fixup(id self, SEL op, ...)) which returns nil (just to see what happens), but this function isn't even being called (the program crashes before calling it). So, my question is, what is callq *l_objc_msgSend_fixup_alloc supposed to do and what is objc_msgSend_fixup (after l_objc_msgSend_fixup_alloc:) supposed to be (a function or an object)? Edit To better explain, I'm not linking my source file against the objc library. What I'm trying to do is implement some parts of the libray, just to see how it works. Here is an approach of what I've done: #include <stdio.h> #include <objc/runtime.h> @interface MyClass { } +(id) alloc; @end @implementation MyClass +(id) alloc { // alloc the object return nil; } @end id objc_msgSend_fixup(id self, SEL op, ...) { printf("Calling objc_msgSend_fixup()...\n"); // looks for the method implementation for SEL in self's vtable return nil; // Since this is just a test, this function doesn't need to do that } int main(int argc, char *argv[]) { MyClass *m; m = [MyClass alloc]; // At this point, according to the assembly code generated // objc_msgSend_fixup should be called. So, the program should, at least, print // "Calling objc_msgSend_fixup()..." on the screen, but it crashes before // objc_msgSend_fixup() is called... return 0; } If the runtime needs to access the object's vtable to find the correct method to call, what is the function which actually does this? I think it is objc_msgSend_fixup, in this case. So, when objc_msgSend_fixup is called, it receives an object as one of its parameters, and, if this object hasn't been initialized, the function fails. So, I've implemented my own version of objc_msgSend_fixup. According to the assembly source above, it should be called. It doesn't matter if the function is actually looking for the implementation of the selector passed as parameter. I just want objc_msgSend_lookup to be called. But, it's not being called, that is, the function that looks for the object's data is not even being called, instead of being called and cause a fault (because it returns a nil (which, by the way, doesn't matter)). The program seg fails before objc_msgSend_lookup is called...

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