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• C++0x optimizing compiler quality

  - by aaa

  hello. I do some heavy numbercrunching and for me floating-point performance is very important. I like performance of Intel compiler very much and quite content with quality of assembly it produces. I am thinking at some point to try C++0x mainly for sugar parts, like auto, initializer list, etc, but also lambdas. at this point I use those features in regular C++ by the means of boost. How good of assembly code do compilers C++0x generate? specifically Intel and gcc compilers. Do they produce SSE code? is performance comparable to C++? are there any benchmarks? My Google search did not reveal much. Thank you.

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• Haskell: Problems with overloading: Interpreter can´t tell which + to use

  - by Ben

  Hi, I want to make functions Double - Double an instance of the Num typeclass. I want to define the sum of two functions as sum of their images. So I wrote instance Num Function where f + g = (\ x - (f x) + (g x)) Here the compiler complains he can´t tell whether I´m using Prelude.+ or Module.+ in the lambda expression. So I imported Prelude qualified as P and wrote instance Num Function where f + g = (\ x - (f x) P.+ (g x)) This compiles just fine, but when I try to add two functions in GHCi the interpreter complains again he can´t tell whether I´m using Prelude.+ or Module.+. Is there any way I can solve this problem?

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• solutions for rapid front-end development?

  - by fayer

  im using mvc framework and i have learned some techniques that help me with different parts of RAD. models: doctrine/visual paradigm controllers/libraries: various design patterns now i only need to know what technique/solution i should use for the views so that i can create views more rapidly. cause i don't think it's efficient to code css/html manually, even though i understand it. its the same principle when using visual paradigm to create both my mysql database tables and doctrine model classes. i believe in using right tools will boost up development speed. so what could i use for the views to save time and energy and don't reinvent the wheel all the time? dreamweaver? any css generation tools? 960/blueprint for layout? suggestions? thanks

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• How do I delete an object from an Entity Framework model without first loading it?

  - by Tomas Lycken

  I am quite sure I've seen the answer to this question somewhere, but as I couldn't find it with a couple of searches on SO or google, I ask it again anyway... In Entity Framework, the only way to delete a data object seems to be MyEntityModel ent = new MyEntityModel(); ent.DeleteObject(theObjectToDelete); ent.SaveChanges(); However, this approach requires the object to be loaded to, in this case, the Controller first, just to delete it. Is there a way to delete a business object referencing only for instance its ID? If there is a smarter way using Linq or Lambda expressions, that is fine too. The main objective, though, is to avoid loading data just to delete it.

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• How to pass a function to a function?

  - by ShaChris23

  Suppose I have a class with 2 static functions: class CommandHandler { public: static void command_one(Item); static void command_two(Item); }; I have a problem DRY problem where I have 2 functions that have the exact same code for every single line, except for the function that it calls: void CommandOne_User() { // some code A CommandHandler::command_one(item); // some code B } void CommandTwo_User() { // some code A CommandHandler::command_two(item); // some code B } I would like to remove duplication, and, ideally, do something like this: void CommandOne_User() { Function func = CommandHandler::command_one(); Refactored_CommandUser(func); } void CommandTwo_User() { Function func = CommandHandler::command_one(); Refactored_CommandUser(func); } void Refactored_CommandUser(Function func) { // some code A func(item); } I have access to Qt, but not Boost. Could someone help suggest a way on how I can refactor something like this?

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• Should we be giving the client's management team direct access to our git hub repository so that the

  - by SharePoint Newbie

  Hi, We are presently working for a client who is new to working with distributed teams. We have teams spread across India and the UK. Although we have decent project tracking tools (Mingle), would it be a good idea to the give the PM at the client access to our git hub repo. Would this be make it easier for them (see what the devs are working on and an insight into what the team has been developing). I agree that noot all commit messages would make sense to them but would this be a good way to boost their confidence in what we are doing? They already can check out our fortnightly releases on our QA and UA environments, but this still is behind dev by 5-6 days. Also, is there any reporting for git hub which makes it easier for PM types to make sense of it all? Thanks

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• mysterious difference between rake test and ruby

  - by standup75

  Here is the mysterious: I have a scope which looks like this (in Image.rb) scope :moderate_all, delegates.where("moderation_flag = #{$moderation_flags[:not_moderated]}") Note that delegates is another scope that I am defining before moderate_all When I leave it like this, I can run my test that checks if an image has been "checked-out" it is not available anymore. I don't put the code of the test, because it does not matter actually. With this code, when I run "rake test" it fails, but if I do "ruby test/unit/image_test.rb" it works! I was thinking I am starting to have a bad day. Then I tried scope :moderate_all, lambda { delegates.where("moderation_flag = #{$moderation_flags[:not_moderated]}") } And "rake test" passes! So my problem is solved, but why?

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• How to check for C++ copy ellision

  - by Steve

  I ran across this article on copy ellision in C++ and I've seen comments about it in the boost library. This is appealing, as I prefer my functions to look like verylargereturntype DoSomething(...) rather than void DoSomething(..., verylargereturntype& retval) So, I have two questions about this Google has virtually no documentation on this at all, how real is this? How can I check that this optimization is actually occuring? I assume it involves looking at the assembly, but lets just say that isn't my strong suit. If anyone can give a very basic example as to what successful ellision looks like, that would be very useful I won't be using copy ellision just to prettify things, but if I can be guaranteed that it works, it sounds pretty useful.

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• Start a thread using a method pointer

  - by Michael

  Hi ! I'm trying to develop a thread abstraction (POSIX thread and thread from the Windows API), and I would very much like it to be able to start them with a method pointer, and not a function pointer. What I would like to do is an abstraction of thread being a class with a pure virtual method "runThread", which would be implanted in the future threaded class. I don't know yet about the Windows thread, but to start a POSIX thread, you need a function pointer, and not a method pointer. And I can't manage to find a way to associate a method with an instance so it could work as a function. I probably just can't find the keywords (and I've been searching a lot), I think it's pretty much what Boost::Bind() does, so it must exist. Can you help me ?

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• How to compare two lists with duplicated items in one list?

  - by eladc

  I need to compare list_a against many others. my problem starts when there's a duplicated item in the other lists (two k's in other_b). my goal is to filter out all the lists with the same items (up to three matching items). list_a = ['j','k','a','7'] other_b = ['k', 'j', 'k', 'q'] other_c = ['k','k','9','k'] >>>filter(lambda x: not x in list_a,other_b) ['q'] I need a way that would return ['k', 'q'], because 'k' appears only once in list_a. comparing list_a and other_c with set() isn't good for my purpose since it will return only one element: k. while I need ['k','9','k'] I hope I was clear enough. Thank you

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• How to understand the functional programming code for converting IP string to a number?

  - by zfz

  In a python discusion, I saw a way to convert IP string to a integer in functional progamming way. Here is the Link . The function is implemented in a single line. def ipnumber(ip): return reduce(lambda sum, chunk: sum <<8 | chunk, map(int, ip.split("."))) However, I have few ideas of funcional programming. Could anybody explain the function in detail? I've some knowledg of "map" and "reduce". But I don't konw what "|" and "chunk" mean here? Thanks.

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• Sharing memory between modules

  - by John Holecek

  Hi, I was wondering how to share some memory between different program modules - lets say, I have a main application (exe), and then some module (dll). They both link to the same static library. This static library will have some manager, that provides various services. What I would like to achieve, is to have this manager shared between all application modules, and to do this transparently during the library initialization. Between processes I could use shared memory, but I want this to be shared in the current process only. Could you think of some cross-platform way to do this? Possibly using boost libraries, if they provide some facilities to do this. Only solution I can think of right now, is to use shared library of the respective OS, that all other modules will link to at runtime, and have the manager saved there.

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• Create an Action<T> to "set" a property, when I am provided with the LINQ Expression for the "get"

  - by Alex

  I'd like to be able to generate a compiled expression to set a property, given the lambda expression that provides the "get" method for a property. Here's what I'm looking for: public Action<int> CreateSetter<T>(Expression<Func<T, int>> getter) { // returns a compiled action using the details of the getter expression tree, or null // if the write property is not defined. } I'm still trying to understand the various types of Expression classes, so if you can point me in the right direction that would be great.

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• How would one call std::forward on all arguments in a variadic function?

  - by Noah Roberts

  I was just writing a generic object factory and using the boost preprocessor meta-library to make a variadic template (using 2010 and it doesn't support them). My function uses rval references and std::forward to do perfect forwarding and it got me thinking...when C++0X comes out and I had a standard compiler I would do this with real variadic templates. How though, would I call std::forward on the arguments? template < typename ... Params void f(Params ... params) // how do I say these are rvalue reference? { y(std::forward(...params)); //? - I doubt this would work. } Only way I can think of would require manual unpacking of ...params and I'm not quite there yet either. Is there a quicker syntax that would work?

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• algorithms that destruct and copy_construct

  - by FredOverflow

  I am currently building my own toy vector for fun, and I was wondering if there is something like the following in the current or next standard or in Boost? template<class T> void destruct(T* begin, T* end) { while (begin != end) { begin -> ~T(); ++begin; } } template<class T> T* copy_construct(T* begin, T* end, T* dst) { while (begin != end) { new(dst) T(*begin); ++begin; ++dst; } return dst; }

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• Image equivalent of ActionLink in ASP.NET MVC

  - by Jason Whitehorn

  In ASP.NET MVC is there an equivalent of the Html.ActionLink helper for Img tags? I have a controller action that outputs a dynamically generated JPEG and I wanted to use the same Lambda expressions to link to it as I do HREFs using ActionLink. Alternatively, a helper that just gives the URL to a route (again specified using Lambdas) would also be acceptable. EDIT: I had originally specified that I was using Preview 5, however I see that a Beta has been released. So all-in-all the version number was an unneeded piece of info as I may be upgrading soon :-)

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• mootools: $ not defined

  - by eaigner

  I've strange error i don't understand. I'm just moving my code from jQuery over to Mootools because it's much cleaner than the jQuery mess. Now when i use the $$('div.canvas') in mootools i get the correct element. When i try $(document).getElement('div.canvas') it tells me that $ is not defined. How can $$ and all helper functions like $lambda etc. be defined but not $? Has something changed there from 1.1 to 1.2 and the docs are not updated yet?

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• Syntax errors on Heroku, but not on local server

  - by Phil_Ken_Sebben

  I'm trying to deploy my first app on Heroku (rails 3). It works fine on my local server, but when I pushed it to Heroku and ran it, it crashes, giving a number of syntax errors. These are related to a collection of scopes I use like the one below: scope :scored, lambda { |score = nil| score.nil? ? {} : where('products.votes_count >= ?', score) } it produces errors of this form: "syntax error, unexpected '=', expecting '|' " "syntax error, unexpected '}', expecting kEND" Why is this syntax making Heroku choke and how can I correct it? Thanks!

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• How do you extend python with C++?

  - by superjoe30

  I've successfully extended python with C, thanks to this handy skeleton module. But I can't find one for C++, and I have circular dependency trouble when trying to fix the errors that C++ gives when I compile this skeleton module. How do you extend Python with C++? I'd rather not depend on Boost (or SWIP or other libraries) if I don't have to. Dependencies are a pain in the butt. Best case scenario, I find a skeleton file that already compiles with C++.

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• toupper/tolower + locale (german)

  - by Oops

  Hi, how to convert a string (wstring) from lowercase to uppercase characters and vice versa? I searched the net and found there is a STL-function std::transform. But until now I hav'nt figured out how to give the right locale-object for example "Germany_german" to the function. Who can help please? my code looks like: wstring strin = L"ABCÄÖÜabcäöü"; wstring str = strin; locale loc( "Germany_german" ); // ??? how to apply this ??? std::transform( str.begin(), str.end(), str.begin(), (int(*)(int)tolower ); //result: "abcäöüabcäöü" The characters ÄÖÜ and äöü (it's like Ae, Oe, Ue) will not be converted correctly. P.S.: I don't prefer a big switch sweat and also I know BOOST is capable of everything, i would prefer a STL solution. thanks in advance Oops

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• Text in gtk.ComboBox without active item

  - by Yotam

  The following PyGTk code, gives a combo-box without an active item. This serves a case where we do not want to have a default, and force the user to select. Still, is there a way to have the empty combo-bar show something like: "Select an item..." without adding a dummy item? import gtk import sys say = sys.stdout.write def cb_changed(w): say("Active index=%d\n" % w.get_active()) topwin = gtk.Window() topwin.set_title("No Default") topwin.set_size_request(0x100, 0x20) topwin.connect('delete-event', gtk.main_quit) vbox = gtk.VBox() ls = gtk.ListStore(str, str) combo = gtk.ComboBox(ls) cell = gtk.CellRendererText() combo.pack_start(cell) combo.add_attribute(cell, 'text', 0) combo.connect('changed', cb_changed) ls.clear() map(lambda i: ls.append(["Item-%d" % i, "Id%d" % i]), range(3)) vbox.pack_start(combo, padding=2) topwin.add(vbox) topwin.show_all() gtk.main() say("%s Exiting\n" % sys.argv[0]) sys.exit(0)

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• Getting list of key values from app config with same name

  - by NoviceMe

  I have follwing in app.config file: <appSettings> <add key="Name" value="Office"/> ... <add key="Name" value="HotSpot"/> ... <add key="Name" value="Home"/> </appSettings> I tried ConfigurationManager.AppSettings["Name"] But it only gives me one Value? How can i get list of all values? I am using c# 3.5. Is there lambda expression or something i can use to get that?

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• python equivalent of filter() getting two output lists

  - by FX

  Let's say I have a list, and a filtering function. Using something like >>> filter(lambda x: x > 10, [1,4,12,7,42]) [12, 42] I can get the elements matching the criterion. Is there a function I could use that would output two lists, one of elements matching, one of the remaining elements? I could call the filter() function twice, but that's kinda ugly :) Edit: the order of elements should be conserved, and I may have identical elements multiple times.

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• Is PThread a good choice for multi-platorm C/C++ multi-threading program?

  - by RogerV

  Been doing mostly Java and smattering of .NET for last five years and haven't written any significant C or C++ during that time. So have been away from that scene for a while. If I want to write a C or C++ program today that does some multi-threading and is source code portable across Windows, Mac OS X, and Linux/Unix - is PThread a good choice? The C or C++ code won't be doing any GUI, so won't need to worry with any of that. For the Windows platform, I don't want to bring a lot of Unix baggage, though, in terms of unix emulation runtime libraries. Would prefer a PThread API for Windows that is a thin-as-possible wrapper over existing Windows threading APIs. ADDENDUM EDIT: Am leaning toward going with boost:thread - I also want to be able to use C++ try/catch exception handling too. And even though my program will be rather minimal and not particularly OOPish, I like to encapsulate using class and namespace - as opposed to C disembodied functions.

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• Make object by it's name

  - by Ockonal

  Hello, is it possible to return exemplar of object using passed type name (string) in c++? I have some base abstract class Base and a few derivates. Example code: class Base { /* ... */ }; class Der1 : public Base { /* ... */ }; class Der2 : public Base { /* ... */ }; And I need function like: Base *objectByType(const std::string &name); Number of derivates classes are changeable and I don't want to make something like switching of name and returning by hands new object type. Is it possible in c++ to do that automatically anyway? p.s. usage should looks like: dynamic_cast<Der1>(objectByType("Der1")); I need pure c++ code (crossplatform). Using boost is permissible.

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