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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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  • Sqlite3 and PDO problem with ORDER BY

    - by Maenny
    Hi, I try to use the SQL statement SELECT * FROM table ORDER BY column via an PDO-Object in PHP. Problem is, that I always get an error (Call to a member function fetchall() on a non-object - that means, the query did not return a PDO-object) when using the names of all columnname EXCEPT for ID. When I query SELECT * FROM table ORDER BY ID it works. ID is the PRIMARY INTEGER KEY, all other columns are TEXT or NUMERIC, neither of them would works with the ORDER BY clause. Any ideas?

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  • Confusing of TTimeSpan usage in Delphi 2010

    - by stanleyxu2005
    Hi All, I tried the new Record type TTimeSpan in Delphi 2010. But I encourage a very strange problem. assert(TTimeSpan.FromMilliseconds(5000).Milliseconds == 5000); This assertion does not pass. The value of 'TTimeSpan.FromMilliseconds(5000).Milliseconds' is always 0. I really cannot explain.

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  • Please help me to deploy merge modules

    - by Dabblernl
    I need to deploy some Crystal Reports XI .dlls (craxdrt.dll, crviewer.dll) to client computers. Craxdrt.dll has many dependencies. I found out that the easiest way to go about this is to use the supplied merge modules. Having always relied on ClikOnce deployment I am at a total loss how to do this. If it matters: the .exe is written in VB6, but I have visual studio 2010 to make setup projects. Thanks!

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  • PHP/CGI: Portable and safe way to get PATH_INFO

    - by LiraNuna
    I'm seeking a portable way to receive the (handy) $_SERVER['PATH_INFO'] variable. After reading a while, it turns out PATH_INFO is originated from CGI/1.1, and my not always be present in all configuration. What is the best (mostly security-wise) way to get that variable - apart from extracting it manually (security concern).

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  • Task Manager with Trac support for Mac

    - by Dmitry
    Found Mylyn as a very good task manager that supports Trac and Gmail Task. I've seen Tasktop, but looking for something with smaller memory footprint that I could always run in background. Is there any lighter client (not on Eclipse platform) to manager at least Trac tasks (via XML-RPC) and in best case scenario with GMail Tasks support?

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  • How can I display different icons for same file extension

    - by ScottCate
    Visual Studio has *.SLN files for 2008, and 2010. In explorer, the icon associated with the file is based on the version somehow. I was always under the impression that the associated icon just looked at the extension, but obviously there is more going on. I'm asking on stack overflow as a developer - for my application, but if you feel this belongs on another forum, I'm happy to move the discussion elsewhere. Thank you!

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  • Variable scope and the 'using' statement in .NET

    - by pete the pagan-gerbil
    If a variable is at class level (ie, private MyDataAccessClass _dataAccess;, can it be used as part of a using statement within the methods of that class to dispose of it correctly? Is it wise to use this method, or is it better to always declare a new variable with a using statement (ie, using (MyDataAccessClass dataAccess = new MyDataAccessClass()) instead of using (_dataAccess = new MyDataAccessClass()))?

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  • declerative_authorization on User problem

    - by Webpain
    I am trying to block all default methods except create and update in my users controller using declerative_authorization. But at the time I add filter_resource_access or filter_access_to into my usersController i always get "Couldn't find User without an ID". Anyone care to explain why this could be happening? class UsersController :new end end def show @user = @current_user end def edit @user = @current_user end def update @user = @current_user # makes our views "cleaner" and more consistent if @user.update_attributes(params[:user]) flash[:notice] = "Account updated!" redirect_to account_url else render :action = :edit end end end

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  • Preconfigure Android Emulator with location?

    - by Janusz
    I want to run automated tests with location on the android emulator. I can setup coordinates via Telnet, but that means starting up a console and manually configuring the emulator before running my junit tests. Is there a possibility to preconfigure the emulator with a KML file or something like that to ensure that there are always coordinates available?

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  • Conditional Join In LINQ?

    - by Soo
    I am trying to write a query that grabs information from one database and joins it to information in a different database. TableA idA valueA idB TableB idB valueB The tricky part is that in TableA, idB isn't always defined, so when I do a normal join, I only get results where TableA has a idB value. What I want is to be able to grab all of the information from TableA even if it doesn't have a corresponding idB value.

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  • Base Case in a recursive method

    - by Shaza
    Hey all, About my question, I'm asking a theoretical question here about Base case or the halting case in a recursive method, what's its standards? I mean, is it standard not to have body in it, just a return statement? Is it always like the following: If(input operation value) return sth; Do you have different thoughts about it??

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  • What language is .NET Framework written in?

    - by chester89
    The question I always wanted to ask and was afraid to, actually - what language is .NET Framework written in? I mean library itself. It seems to me that it was C and C++ mostly. (I hope Jon Skeet is reading this one, it`ll be very interesting to hear what he thinks about it)

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  • Java: JButton actionListener explantation

    - by MrDoctorProfessorTyler
    I am extremely confused as to how a JButton works. I have read over the oracle documents of the JButton, but I have failed to see how a JButton can have an actionlistener added to it. I have really always wondered how things like JFrames and all that can have things like .addMouseListener and all that. Can anyone explain how a JButton can have an actionListener added to it like the .addActionListener(...) syntax?

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  • To change svn revision text

    - by uzay95
    I wrote a script which can auto commit in every 10 minutes. But it's commit message always same ("Code saved"). But i want to change some of them which are milestone. This is my auto commit script: cd c:\inetpub\wwwroot\siteCodes svn commit -m "Code Saved" How can i write a script which can give me a chance to write revision number and new commit message.

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  • Which user account to assign as owner when attaching an SQL Server database?

    - by FreshCode
    This is a simple database security & performance question, but I've always used either a special user (eg. mydbuser), or Windows' built-in NETWORK SECURITY account as the owner when attaching databases to my SQL Server instances. When deploying my database to a production server, is there a specific user I should stick to or avoid? I would think that using an account with a set password could open the database up to a potential security issue.

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  • R segfault when running via Rpy on linux

    - by Zhang18
    I'm running R via Rpy on a redhat linux distribution. Periodically I'll encounter this error message: *** caught segfault *** address (nil), cause 'unknown' And the entire program dies right there. It usually occurs when I run a lot of regression r.lm(). But by simply running the identical code again, the problem may or may not go away (so not always reproduceable). Does anyone know what might be causing this, and/or how I can prevent it from happening?

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  • Need to Post json data using jQuery.ajax

    - by Anil Bhat
    I have a json of the following format which I need to send in the Ajax request through POST method: { “gbus”: [ { "code": "*" } ], “regions”: [ { "code": "*" } ], “offices”: [ { "code": "*" } ], “contracttypes”: [ { "code": "*" } ], “jobnumbers”: [ { "code": "*" } ], “disciplines”: [ { "code": "*" } ] } Its not working for me, giving 500 error always when I try to submit it. Please suggest if you have any idea.

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