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  • Optimizing hash lookup & memory performance in Go

    - by Moishe
    As an exercise, I'm implementing HashLife in Go. In brief, HashLife works by memoizing nodes in a quadtree so that once a given node's value in the future has been calculated, it can just be looked up instead of being re-calculated. So eg. if you have a node at the 8x8 level, you remember it by its four children (each at the 2x2 level). So next time you see an 8x8 node, when you calculate the next generation, you first check if you've already seen a node with those same four children. This is extended up through all levels of the quadtree, which gives you some pretty amazing optimizations if eg. you're 10 levels above the leaves. Unsurprisingly, it looks like the perfmance crux of this is the lookup of nodes by child-node values. Currently I have a hashmap of {&upper_left_node,&upper_right_node,&lower_left_node,&lower_right_node} -> node So my lookup function is this: func FindNode(ul, ur, ll, lr *Node) *Node { var node *Node var ok bool nc := NodeChildren{ul, ur, ll, lr} node, ok = NodeMap[nc] if ok { return node } node = &Node{ul, ur, ll, lr, 0, ul.Level + 1, nil} NodeMap[nc] = node return node } What I'm trying to figure out is if the "nc := NodeChildren..." line causes a memory allocation each time the function is called. If it does, can I/should I move the declaration to the global scope and just modify the values each time this function is called? Or is there a more efficient way to do this? Any advice/feedback would be welcome. (even coding style nits; this is literally the first thing I've written in Go so I'd love any feedback)

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  • Code Reuse is (Damn) Hard

    - by James Michael Hare
    Being a development team lead, the task of interviewing new candidates was part of my job.  Like any typical interview, we started with some easy questions to get them warmed up and help calm their nerves before hitting the hard stuff. One of those easier questions was almost always: “Name some benefits of object-oriented development.”  Nearly every time, the candidate would chime in with a plethora of canned answers which typically included: “it helps ease code reuse.”  Of course, this is a gross oversimplification.  Tools only ease reuse, its developers that ultimately can cause code to be reusable or not, regardless of the language or methodology. But it did get me thinking…  we always used to say that as part of our mantra as to why Object-Oriented Programming was so great.  With polymorphism, inheritance, encapsulation, etc. we in essence set up the concepts to help facilitate reuse as much as possible.  And yes, as a developer now of many years, I unquestionably held that belief for ages before it really struck me how my views on reuse have jaded over the years.  In fact, in many ways Agile rightly eschews reuse as taking a backseat to developing what's needed for the here and now.  It used to be I was in complete opposition to that view, but more and more I've come to see the logic in it.  Too many times I've seen developers (myself included) get lost in design paralysis trying to come up with the perfect abstraction that would stand all time.  Nearly without fail, all of these pieces of code become obsolete in a matter of months or years. It’s not that I don’t like reuse – it’s just that reuse is hard.  In fact, reuse is DAMN hard.  Many times it is just a distraction that eats up architect and developer time, and worse yet can be counter-productive and force wrong decisions.  Now don’t get me wrong, I love the idea of reusable code when it makes sense.  These are in the few cases where you are designing something that is inherently reusable.  The problem is, most business-class code is inherently unfit for reuse! Furthermore, the code that is reusable will often fail to be reused if you don’t have the proper framework in place for effective reuse that includes standardized versioning, building, releasing, and documenting the components.  That should always be standard across the board when promoting reusable code.  All of this is hard, and it should only be done when you have code that is truly reusable or you will be exerting a large amount of development effort for very little bang for your buck. But my goal here is not to get into how to reuse (that is a topic unto itself) but what should be reused.  First, let’s look at an extension method.  There’s many times where I want to kick off a thread to handle a task, then when I want to reign that thread in of course I want to do a Join on it.  But what if I only want to wait a limited amount of time and then Abort?  Well, I could of course write that logic out by hand each time, but it seemed like a great extension method: 1: public static class ThreadExtensions 2: { 3: public static bool JoinOrAbort(this Thread thread, TimeSpan timeToWait) 4: { 5: bool isJoined = false; 6:  7: if (thread != null) 8: { 9: isJoined = thread.Join(timeToWait); 10:  11: if (!isJoined) 12: { 13: thread.Abort(); 14: } 15: } 16: return isJoined; 17: } 18: } 19:  When I look at this code, I can immediately see things that jump out at me as reasons why this code is very reusable.  Some of them are standard OO principles, and some are kind-of home grown litmus tests: Single Responsibility Principle (SRP) – The only reason this extension method need change is if the Thread class itself changes (one responsibility). Stable Dependencies Principle (SDP) – This method only depends on classes that are more stable than it is (System.Threading.Thread), and in itself is very stable, hence other classes may safely depend on it. It is also not dependent on any business domain, and thus isn't subject to changes as the business itself changes. Open-Closed Principle (OCP) – This class is inherently closed to change. Small and Stable Problem Domain – This method only cares about System.Threading.Thread. All-or-None Usage – A user of a reusable class should want the functionality of that class, not parts of that functionality.  That’s not to say they most use every method, but they shouldn’t be using a method just to get half of its result. Cost of Reuse vs. Cost to Recreate – since this class is highly stable and minimally complex, we can offer it up for reuse very cheaply by promoting it as “ready-to-go” and already unit tested (important!) and available through a standard release cycle (very important!). Okay, all seems good there, now lets look at an entity and DAO.  I don’t know about you all, but there have been times I’ve been in organizations that get the grand idea that all DAOs and entities should be standardized and shared.  While this may work for small or static organizations, it’s near ludicrous for anything large or volatile. 1: namespace Shared.Entities 2: { 3: public class Account 4: { 5: public int Id { get; set; } 6:  7: public string Name { get; set; } 8:  9: public Address HomeAddress { get; set; } 10:  11: public int Age { get; set;} 12:  13: public DateTime LastUsed { get; set; } 14:  15: // etc, etc, etc... 16: } 17: } 18:  19: ... 20:  21: namespace Shared.DataAccess 22: { 23: public class AccountDao 24: { 25: public Account FindAccount(int id) 26: { 27: // dao logic to query and return account 28: } 29:  30: ... 31:  32: } 33: } Now to be fair, I’m not saying there doesn’t exist an organization where some entites may be extremely static and unchanging.  But at best such entities and DAOs will be problematic cases of reuse.  Let’s examine those same tests: Single Responsibility Principle (SRP) – The reasons to change for these classes will be strongly dependent on what the definition of the account is which can change over time and may have multiple influences depending on the number of systems an account can cover. Stable Dependencies Principle (SDP) – This method depends on the data model beneath itself which also is largely dependent on the business definition of an account which can be very inherently unstable. Open-Closed Principle (OCP) – This class is not really closed for modification.  Every time the account definition may change, you’d need to modify this class. Small and Stable Problem Domain – The definition of an account is inherently unstable and in fact may be very large.  What if you are designing a system that aggregates account information from several sources? All-or-None Usage – What if your view of the account encompasses data from 3 different sources but you only care about one of those sources or one piece of data?  Should you have to take the hit of looking up all the other data?  On the other hand, should you have ten different methods returning portions of data in chunks people tend to ask for?  Neither is really a great solution. Cost of Reuse vs. Cost to Recreate – DAOs are really trivial to rewrite, and unless your definition of an account is EXTREMELY stable, the cost to promote, support, and release a reusable account entity and DAO are usually far higher than the cost to recreate as needed. It’s no accident that my case for reuse was a utility class and my case for non-reuse was an entity/DAO.  In general, the smaller and more stable an abstraction is, the higher its level of reuse.  When I became the lead of the Shared Components Committee at my workplace, one of the original goals we looked at satisfying was to find (or create), version, release, and promote a shared library of common utility classes, frameworks, and data access objects.  Now, of course, many of you will point to nHibernate and Entity for the latter, but we were looking at larger, macro collections of data that span multiple data sources of varying types (databases, web services, etc). As we got deeper and deeper in the details of how to manage and release these items, it quickly became apparent that while the case for reuse was typically a slam dunk for utilities and frameworks, the data access objects just didn’t “smell” right.  We ended up having session after session of design meetings to try and find the right way to share these data access components. When someone asked me why it was taking so long to iron out the shared entities, my response was quite simple, “Reuse is hard...”  And that’s when I realized, that while reuse is an awesome goal and we should strive to make code maintainable, often times you end up creating far more work for yourself than necessary by trying to force code to be reusable that inherently isn’t. Think about classes the times you’ve worked in a company where in the design session people fight over the best way to implement a class to make it maximally reusable, extensible, and any other buzzwordable.  Then think about how quickly that design became obsolete.  Many times I set out to do a project and think, “yes, this is the best design, I can extend it easily!” only to find out the business requirements change COMPLETELY in such a way that the design is rendered invalid.  Code, in general, tends to rust and age over time.  As such, writing reusable code can often be difficult and many times ends up being a futile exercise and worse yet, sometimes makes the code harder to maintain because it obfuscates the design in the name of extensibility or reusability. So what do I think are reusable components? Generic Utility classes – these tend to be small classes that assist in a task and have no business context whatsoever. Implementation Abstraction Frameworks – home-grown frameworks that try to isolate changes to third party products you may be depending on (like writing a messaging abstraction layer for publishing/subscribing that is independent of whether you use JMS, MSMQ, etc). Simplification and Uniformity Frameworks – To some extent this is similar to an abstraction framework, but there may be one chosen provider but a development shop mandate to perform certain complex items in a certain way.  Or, perhaps to simplify and dumb-down a complex task for the average developer (such as implementing a particular development-shop’s method of encryption). And what are less reusable? Application and Business Layers – tend to fluctuate a lot as requirements change and new features are added, so tend to be an unstable dependency.  May be reused across applications but also very volatile. Entities and Data Access Layers – these tend to be tuned to the scope of the application, so reusing them can be hard unless the abstract is very stable. So what’s the big lesson?  Reuse is hard.  In fact it’s damn hard.  And much of the time I’m not convinced we should focus too hard on it. If you’re designing a utility or framework, then by all means design it for reuse.  But you most also really set down a good versioning, release, and documentation process to maximize your chances.  For anything else, design it to be maintainable and extendable, but don’t waste the effort on reusability for something that most likely will be obsolete in a year or two anyway.

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  • SFML programs fails to debug with glslDevil

    - by Zhen
    I'm testing the glslDevil debugger with a simple (and working) SFML application in Linux + NVidia. But it always fails in the window creation step: W! Program Start | glXGetConfig(0x86a50b0, 0x86acef8, 4, 0xbf8228c4) | glXGetConfig(0x86a50b0, 0x86acef8, 5, 0xbf8228c8) | glXGetConfig(0x86a50b0, 0x86acef8, 8, 0xbf8228cc) | glXGetConfig(0x86a50b0, 0x86acef8, 9, 0xbf8228d0) | glXGetConfig(0x86a50b0, 0x86acef8, 10, 0xbf8228d4) | glXGetConfig(0x86a50b0, 0x86acef8, 11, 0xbf8228d8) | glXGetConfig(0x86a50b0, 0x86acef8, 12, 0xbf8228dc) | glXGetConfig(0x86a50b0, 0x86acef8, 13, 0xbf8228e0) | glXGetConfig(0x86a50b0, 0x86acef8, 100000, 0xbf8228e4) | glXGetConfig(0x86a50b0, 0x86acef8, 100001, 0xbf8228e8) | glXCreateContext(0x86a50b0, 0x86acef8, (nil), 1) E! Child process exited W! Program termination forced! And the code that fails: #include <SFML/Graphics.hpp> #define GL_GLEXT_PROTOTYPES 1 #define GL3_PROTOTYPES 1 #include <GL/gl.h> #include <GL/glu.h> #include <GL/glext.h> int main(){ sf::RenderWindow window{ sf::VideoMode(800, 600), "Test SFML+GL" }; bool running = true; while( running ){ sf::Event event; while( window.pollEvent(event) ){ if( event.type == sf::Event::Closed ){ running = false; }else if(event.type == sf::Event::Resized){ glViewport(0, 0, event.size.width, event.size.height); } } window.display(); } return 0; } Is It posible to solve this problem? or get around the problem to continue the gslsDevil use?.

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  • Building LMMS: "Configuring incomplete, errors occurred!"

    - by fridojet
    I tried to build Linux MultiMedia studio from the source of the SourceForge git:// repository under Ubuntu 12.04 LTS 32b: git clone git://lmms.git.sourceforge.net/gitroot/lmms/lmms cd lmms git checkout First I tried to install all the required libraries and then I cmaked. - That's what happened on cmake (errors occurred!): [DIR]lmms/build$ cmake .. -- The C compiler identification is GNU -- The CXX compiler identification is GNU -- Check for working C compiler: /usr/bin/gcc -- Check for working C compiler: /usr/bin/gcc -- works -- Detecting C compiler ABI info -- Detecting C compiler ABI info - done -- Check for working CXX compiler: /usr/bin/c++ -- Check for working CXX compiler: /usr/bin/c++ -- works -- Detecting CXX compiler ABI info -- Detecting CXX compiler ABI info - done PROCESSOR: i686 Machine: i686-linux-gnu -- Target host is 32 bit -- Looking for include files LMMS_HAVE_STDINT_H -- Looking for include files LMMS_HAVE_STDINT_H - found -- Looking for include files LMMS_HAVE_STDBOOL_H -- Looking for include files LMMS_HAVE_STDBOOL_H - found -- Looking for include files LMMS_HAVE_STDLIB_H -- Looking for include files LMMS_HAVE_STDLIB_H - found -- Looking for include files LMMS_HAVE_PTHREAD_H -- Looking for include files LMMS_HAVE_PTHREAD_H - found -- Looking for include files LMMS_HAVE_SEMAPHORE_H -- Looking for include files LMMS_HAVE_SEMAPHORE_H - found -- Looking for include files LMMS_HAVE_UNISTD_H -- Looking for include files LMMS_HAVE_UNISTD_H - found -- Looking for include files LMMS_HAVE_SYS_TYPES_H -- Looking for include files LMMS_HAVE_SYS_TYPES_H - found -- Looking for include files LMMS_HAVE_SYS_IPC_H -- Looking for include files LMMS_HAVE_SYS_IPC_H - found -- Looking for include files LMMS_HAVE_SYS_SHM_H -- Looking for include files LMMS_HAVE_SYS_SHM_H - found -- Looking for include files LMMS_HAVE_SYS_TIME_H -- Looking for include files LMMS_HAVE_SYS_TIME_H - found -- Looking for include files LMMS_HAVE_SYS_WAIT_H -- Looking for include files LMMS_HAVE_SYS_WAIT_H - found -- Looking for include files LMMS_HAVE_SYS_SELECT_H -- Looking for include files LMMS_HAVE_SYS_SELECT_H - found -- Looking for include files LMMS_HAVE_STDARG_H -- Looking for include files LMMS_HAVE_STDARG_H - found -- Looking for include files LMMS_HAVE_SIGNAL_H -- Looking for include files LMMS_HAVE_SIGNAL_H - found -- Looking for include files LMMS_HAVE_SCHED_H -- Looking for include files LMMS_HAVE_SCHED_H - found -- Looking for include files LMMS_HAVE_SYS_SOUNDCARD_H -- Looking for include files LMMS_HAVE_SYS_SOUNDCARD_H - found -- Looking for include files LMMS_HAVE_SOUNDCARD_H -- Looking for include files LMMS_HAVE_SOUNDCARD_H - not found. -- Looking for include files LMMS_HAVE_FCNTL_H -- Looking for include files LMMS_HAVE_FCNTL_H - found -- Looking for include files LMMS_HAVE_SYS_IOCTL_H -- Looking for include files LMMS_HAVE_SYS_IOCTL_H - found -- Looking for include files LMMS_HAVE_CTYPE_H -- Looking for include files LMMS_HAVE_CTYPE_H - found -- Looking for include files LMMS_HAVE_STRING_H -- Looking for include files LMMS_HAVE_STRING_H - found -- Looking for include files LMMS_HAVE_PROCESS_H -- Looking for include files LMMS_HAVE_PROCESS_H - not found. -- Looking for include files LMMS_HAVE_LOCALE_H -- Looking for include files LMMS_HAVE_LOCALE_H - found -- Looking for Q_WS_X11 -- Looking for Q_WS_X11 - found -- Looking for Q_WS_WIN -- Looking for Q_WS_WIN - not found. -- Looking for Q_WS_QWS -- Looking for Q_WS_QWS - not found. -- Looking for Q_WS_MAC -- Looking for Q_WS_MAC - not found. -- Found Qt4: /usr/bin/qmake (found suitable version "4.8.1", required is "4.6.0;COMPONENTS;QtCore;QtGui;QtXml;QtNetwork") -- Found Qt translations in /usr/share/qt4/translations -- checking for module 'sndfile>=1.0.11' -- found sndfile, version 1.0.25 -- Looking for include files CMAKE_HAVE_PTHREAD_H -- Looking for include files CMAKE_HAVE_PTHREAD_H - found -- Looking for pthread_create in pthreads -- Looking for pthread_create in pthreads - not found -- Looking for pthread_create in pthread -- Looking for pthread_create in pthread - found -- Found Threads: TRUE -- Found libzip: /usr/lib/libzip.so -- Found libflac++: /usr/lib/i386-linux-gnu/libFLAC.so;/usr/lib/i386-linux-gnu/libFLAC++.so -- Found STK: /usr/lib/i386-linux-gnu/libstk.so -- checking for module 'portaudio-2.0' -- found portaudio-2.0, version 19 -- Found Portaudio: portaudio;asound;m;pthread -- checking for module 'libpulse' -- found libpulse, version 1.1 -- Found PulseAudio Simple: /usr/lib/i386-linux-gnu/libpulse.so -- Looking for vorbis_bitrate_addblock in vorbis -- Looking for vorbis_bitrate_addblock in vorbis - found -- Found OggVorbis: /usr/lib/i386-linux-gnu/libogg.so;/usr/lib/i386-linux-gnu/libvorbis.so;/usr/lib/i386-linux-gnu/libvorbisfile.so;/usr/lib/i386-linux-gnu/libvorbisenc.so -- Looking for snd_seq_create_simple_port in asound -- Looking for snd_seq_create_simple_port in asound - found -- Found ALSA: /usr/lib/i386-linux-gnu/libasound.so -- Looking for include files LMMS_HAVE_MACHINE_SOUNDCARD_H -- Looking for include files LMMS_HAVE_MACHINE_SOUNDCARD_H - not found. -- Looking for include files LMMS_HAVE_LINUX_AWE_VOICE_H -- Looking for include files LMMS_HAVE_LINUX_AWE_VOICE_H - not found. -- Looking for include files LMMS_HAVE_AWE_VOICE_H -- Looking for include files LMMS_HAVE_AWE_VOICE_H - not found. -- Looking for include files LMMS_HAVE__USR_SRC_SYS_I386_ISA_SOUND_AWE_VOICE_H -- Looking for include files LMMS_HAVE__USR_SRC_SYS_I386_ISA_SOUND_AWE_VOICE_H - not found. -- Looking for include files LMMS_HAVE__USR_SRC_SYS_GNU_I386_ISA_SOUND_AWE_VOICE_H -- Looking for include files LMMS_HAVE__USR_SRC_SYS_GNU_I386_ISA_SOUND_AWE_VOICE_H - not found. -- Looking for C++ include sys/asoundlib.h -- Looking for C++ include sys/asoundlib.h - found -- Looking for C++ include alsa/asoundlib.h -- Looking for C++ include alsa/asoundlib.h - found -- Looking for snd_pcm_resume in asound -- Looking for snd_pcm_resume in asound - found -- checking for module 'jack>=0.77' -- found jack, version 0.121.2 -- checking for module 'fftw3f>=3.0.0' -- package 'fftw3f>=3.0.0' not found CMake Error at /usr/share/cmake-2.8/Modules/FindPkgConfig.cmake:266 (message): A required package was not found Call Stack (most recent call first): /usr/share/cmake-2.8/Modules/FindPkgConfig.cmake:320 (_pkg_check_modules_internal) CMakeLists.txt:309 (PKG_CHECK_MODULES) -- checking for module 'fluidsynth>=1.0.7' -- found fluidsynth, version 1.1.5 -- Looking for include files LMMS_HAVE_LV2CORE -- Looking for include files LMMS_HAVE_LV2CORE - found -- Looking for include files LMMS_HAVE_SLV2_SCALEPOINTS_H -- Looking for include files LMMS_HAVE_SLV2_SCALEPOINTS_H - not found. -- Looking for slv2_world_new in slv2 -- Looking for slv2_world_new in slv2 - found -- Looking for librdf_new_world in rdf -- Looking for librdf_new_world in rdf - found -- Looking for wine_init in wine -- Looking for wine_init in wine - found -- Looking for C++ include windows.h -- Looking for C++ include windows.h - found -- checking for module 'samplerate>=0.1.7' -- package 'samplerate>=0.1.7' not found -- Performing Test HAVE_LRINT -- Performing Test HAVE_LRINT - Success -- Performing Test HAVE_LRINTF -- Performing Test HAVE_LRINTF - Success -- Performing Test CPU_CLIPS_POSITIVE -- Performing Test CPU_CLIPS_POSITIVE - Failed -- Performing Test CPU_CLIPS_NEGATIVE -- Performing Test CPU_CLIPS_NEGATIVE - Success -- Looking for XOpenDisplay in /usr/lib/i386-linux-gnu/libX11.so;/usr/lib/i386-linux-gnu/libXext.so -- Looking for XOpenDisplay in /usr/lib/i386-linux-gnu/libX11.so;/usr/lib/i386-linux-gnu/libXext.so - found -- Looking for gethostbyname -- Looking for gethostbyname - found -- Looking for connect -- Looking for connect - found -- Looking for remove -- Looking for remove - found -- Looking for shmat -- Looking for shmat - found -- Looking for IceConnectionNumber in ICE -- Looking for IceConnectionNumber in ICE - found -- Found X11: /usr/lib/i386-linux-gnu/libX11.so -- Found Freetype: /usr/lib/i386-linux-gnu/libfreetype.so Installation Summary -------------------- * Install Directory : /usr/local * Use system's libsamplerate : Supported audio interfaces -------------------------- * ALSA : OK * JACK : OK * OSS : OK * PortAudio : OK * PulseAudio : OK * SDL : OK Supported MIDI interfaces ------------------------- * ALSA : OK * OSS : OK * WinMM : <not supported on this platform> Supported file formats for project export ----------------------------------------- * WAVE : OK * OGG/VORBIS : OK * FLAC : OK Optional plugins ---------------- * SoundFont2 player : OK * Stk Mallets : OK * VST-instrument hoster : OK * VST-effect hoster : OK * LV2 hoster : OK * CALF LADSPA plugins : OK * CAPS LADSPA plugins : OK * CMT LADSPA plugins : OK * TAP LADSPA plugins : OK * SWH LADSPA plugins : OK * FL .zip import : OK ----------------------------------------------------------------- IMPORTANT: after installing missing packages, remove CMakeCache.txt before running cmake again! ----------------------------------------------------------------- -- Configuring incomplete, errors occurred! Here are some parts the contents of my lmms/build/CMakeCache.txt file: # This is the CMakeCache file. # For build in directory: /home/jk/Downloads/lmms-git/lmms/build # It was generated by CMake: /usr/bin/cmake # You can edit this file to change values found and used by cmake. # If you do not want to change any of the values, simply exit the editor. # If you do want to change a value, simply edit, save, and exit the editor. # The syntax for the file is as follows: # KEY:TYPE=VALUE # KEY is the name of a variable in the cache. # TYPE is a hint to GUI's for the type of VALUE, DO NOT EDIT TYPE!. # VALUE is the current value for the KEY. ######################## # EXTERNAL cache entries ######################## //Path to a file. ALSA_INCLUDES:PATH=/usr/include //Path to a library. ASOUND_LIBRARY:FILEPATH=/usr/lib/i386-linux-gnu/libasound.so //Path to a program. CMAKE_AR:FILEPATH=/usr/bin/ar //Choose the type of build, options are: None(CMAKE_CXX_FLAGS or // CMAKE_C_FLAGS used) Debug Release RelWithDebInfo MinSizeRel. CMAKE_BUILD_TYPE:STRING= //Enable/Disable color output during build. CMAKE_COLOR_MAKEFILE:BOOL=ON //CXX compiler. CMAKE_CXX_COMPILER:FILEPATH=/usr/bin/c++ //Flags used by the compiler during all build types. CMAKE_CXX_FLAGS:STRING= //Flags used by the compiler during debug builds. CMAKE_CXX_FLAGS_DEBUG:STRING=-g //Flags used by the compiler during release minsize builds. CMAKE_CXX_FLAGS_MINSIZEREL:STRING=-Os -DNDEBUG //Flags used by the compiler during release builds (/MD /Ob1 /Oi // /Ot /Oy /Gs will produce slightly less optimized but smaller // files). CMAKE_CXX_FLAGS_RELEASE:STRING=-O3 -DNDEBUG //Flags used by the compiler during Release with Debug Info builds. CMAKE_CXX_FLAGS_RELWITHDEBINFO:STRING=-O2 -g //C compiler. CMAKE_C_COMPILER:FILEPATH=/usr/bin/gcc //Flags used by the compiler during all build types. CMAKE_C_FLAGS:STRING= //Flags used by the compiler during debug builds. CMAKE_C_FLAGS_DEBUG:STRING=-g //Flags used by the compiler during release minsize builds. CMAKE_C_FLAGS_MINSIZEREL:STRING=-Os -DNDEBUG //Flags used by the compiler during release builds (/MD /Ob1 /Oi // /Ot /Oy /Gs will produce slightly less optimized but smaller // files). CMAKE_C_FLAGS_RELEASE:STRING=-O3 -DNDEBUG //Flags used by the compiler during Release with Debug Info builds. CMAKE_C_FLAGS_RELWITHDEBINFO:STRING=-O2 -g //Flags used by the linker. CMAKE_EXE_LINKER_FLAGS:STRING=' ' //Flags used by the linker during debug builds. CMAKE_EXE_LINKER_FLAGS_DEBUG:STRING= //Flags used by the linker during release minsize builds. CMAKE_EXE_LINKER_FLAGS_MINSIZEREL:STRING= //Flags used by the linker during release builds. CMAKE_EXE_LINKER_FLAGS_RELEASE:STRING= //Flags used by the linker during Release with Debug Info builds. CMAKE_EXE_LINKER_FLAGS_RELWITHDEBINFO:STRING= //Enable/Disable output of compile commands during generation. CMAKE_EXPORT_COMPILE_COMMANDS:BOOL=OFF //Install path prefix, prepended onto install directories. CMAKE_INSTALL_PREFIX:PATH=/usr/local //Path to a program. CMAKE_LINKER:FILEPATH=/usr/bin/ld //Path to a program. CMAKE_MAKE_PROGRAM:FILEPATH=/usr/bin/make //Flags used by the linker during the creation of modules. CMAKE_MODULE_LINKER_FLAGS:STRING=' ' //Flags used by the linker during debug builds. CMAKE_MODULE_LINKER_FLAGS_DEBUG:STRING= //Flags used by the linker during release minsize builds. CMAKE_MODULE_LINKER_FLAGS_MINSIZEREL:STRING= //Flags used by the linker during release builds. CMAKE_MODULE_LINKER_FLAGS_RELEASE:STRING= //Flags used by the linker during Release with Debug Info builds. CMAKE_MODULE_LINKER_FLAGS_RELWITHDEBINFO:STRING= ==[...]== That's a list of the contents of my lmms/build folder: [DIR]lmms/build$ dir CMakeCache.txt CPackSourceConfig.cmake lmmsconfig.h plugins CMakeFiles data lmms.rc CPackConfig.cmake include lmmsversion.h My Question: It just tells me that that "errors" occurred, but I can't see any error message. It seems like everything went fine. - So: Any idea what the problem could be? - Thanks.

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  • Is it bad idea to use flag variable to search MAX element in array?

    - by Boris Treukhov
    Over my programming career I formed a habit to introduce a flag variable that indicates that the first comparison has occured, just like Msft does in its linq Max() extension method implementation public static int Max(this IEnumerable<int> source) { if (source == null) { throw Error.ArgumentNull("source"); } int num = 0; bool flag = false; foreach (int num2 in source) { if (flag) { if (num2 > num) { num = num2; } } else { num = num2; flag = true; } } if (!flag) { throw Error.NoElements(); } return num; } However I have met some heretics lately, who implement this by just starting with the first element and assigning it to result, and oh no - it turned out that STL and Java authors have preferred the latter method. Java: public static <T extends Object & Comparable<? super T>> T max(Collection<? extends T> coll) { Iterator<? extends T> i = coll.iterator(); T candidate = i.next(); while (i.hasNext()) { T next = i.next(); if (next.compareTo(candidate) > 0) candidate = next; } return candidate; } STL: template<class _FwdIt> inline _FwdIt _Max_element(_FwdIt _First, _FwdIt _Last) { // find largest element, using operator< _FwdIt _Found = _First; if (_First != _Last) for (; ++_First != _Last; ) if (_DEBUG_LT(*_Found, *_First)) _Found = _First; return (_Found); } Are there any preferences between one method or another? Are there any historical reasons for this? Is one method more dangerous than another?

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  • Image with FadeIn effect blinks when added to scene

    - by Ef Es
    I am trying to add an image to the scene, but it should just be added to the scene invisible, FadeIn and then be deleted when the effect finishes. My problem is that the images blink once when they are added to the scene, then they do the intended effect. My best guess is that when they are added they show on the scene for a split second before starting the animation. I though of making them invisible for a split second before activating them, but I am not sure how to code it. const bool Sunbeams::add() { const CCSize kSceenSize = CCDirector::sharedDirector()->getWinSize(); const int nRayType = random( m_kRays.size()); const CCPoint kPosition( random( static_cast < int >( kSceenSize.width)), 0.0f); const float fDuration = random( m_fDurationVariance) + m_fDurationMin; CCSprite* pkLightBeam = CCSprite::spriteWithTexture( m_kRays[nRayType]); if ( !pkLightBeam) { msg::debug( "Sunbeams::add", "Failed to create sprite from ray '%d'!\n", m_kRays[nRayType]); return false; } pkLightBeam->setAnchorPoint( CCPointZero); pkLightBeam->setPosition( kPosition); m_kActiveBeams.push_back( pkLightBeam); CCDirector::sharedDirector()->getRunningScene()->addChild( pkLightBeam); CCActionInterval* pkAction = CCFadeIn::actionWithDuration( fDuration); CCActionInterval* pkActionBack = pkAction->reverse(); pkLightBeam->runAction( CCSequence::actions( pkAction, pkActionBack, 0)); return true; }

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  • how to find and filter blobs from segment image using python?

    - by Python Team
    Am trying to detect number plate from an image.I have converted an image to grayscale and segment image. Now i have to find and filter blobs from an image and to detect number plate from an image. I will explain what i did.. I jus read segment image license_plate = cv2.imread('license1_segmented.png',cv2.CV_LOAD_IMAGE_COLOR) license_plate_size = (license_plate.shape[1], license_plate.shape[0]) mask = cv2.cv.CreateImage (license_plate_size, 8, 1) cv2.cv.Set(mask, 1) thresh_image_ipl = cv2.cv.CreateImage(license_plate_size, cv2.cv.IPL_DEPTH_8U, 1) cv2.cv.SetData(thresh_image_ipl,thresh_image.tostring(),thresh_image.dtype.itemsize * 1 * thresh_image.shape[1]) min_blob_size = 100 # Blob must be 30 px by 30 px max_blob_size = 10000 threshold = 100 **myblobs = CBlobResult(thresh_image_ipl,mask, threshold, True)** myblobs.filter_blobs(min_blob_size, max_blob_size) blob_count = myblobs.GetNumBlobs() trying to find and filter blobs from an image.But am getting error while passing the parameters to CBlobResult which i highlighted above code.I mentioned the error below what i get while passing. Traceback (most recent call last): File "rectdetect1.py", line 110, in <module> myblobs = CBlobResult(thresh_image_ipl,image_area, threshold, True) File "/home/oomsys/pyblobs-read-only/blobs/BlobResult.py", line 92, in __init__ this = _BlobResult.new_CBlobResult(*args) NotImplementedError: Wrong number or type of arguments for overloaded function 'new_CBlobResult'. Possible C/C++ prototypes are: CBlobResult::CBlobResult() CBlobResult::CBlobResult(IplImage *,IplImage *,int,bool) CBlobResult::CBlobResult(CBlobResult const &) Anyone help me to find out the erros and to solve this and all... Thanks in advance...

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  • Identify which CCSprite is touched in Cocos2d

    - by PeterK
    I am trying to learn Cocos2d and is experimenting with Ray Wenderlich tutorial whack-a-mole: www.raywenderlich.com/2560/how-to-create-a-mole-whacking-game-with-cocos2d-part-1 In this tutorial three CCSprite's are popping up and you should click on them... However, i am trying to identify which mole, rat in my case, is popping up and place a CCSprite above that. Initially this looked like an easy task but i am failing. I am trying to NSLog LEFT HIT. i would guess the problem is in the If-statement and the last "227" height parameter. The left rat boundingBox = {{99.5, 146.5}, {165, 227}} (from NSLog). The key code is in the ccTouchBegan function: -(BOOL) ccTouchBegan:(UITouch *)touch withEvent:(UIEvent *)event { CGPoint touchLocation = [self convertTouchToNodeSpace:touch]; for (CCSprite *rat in rats) { if (rat.userData == FALSE) continue; if (CGRectContainsPoint(rat.boundingBox, touchLocation)) { //left: rat boundingBox = {{99.5, 146.5}, {165, 227}} //mid: rat boundingBox = {{349.5, 146.5}, {165, 227}} //right: rat boundingBox = {{599.5, 146.5}, {165, 227}} //>>>>Here is where i try to get a hit<<<< if (CGRectContainsPoint(CGRectMake(99.5, 146.55, 165, 227), touchLocation)) { NSLog(@">>>>HIT LEFT<<<<<"); } I would really appreciate a few ideas how to get this to work.

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  • PLINQ Adventure Land - WaitForAll

    - by adweigert
    PLINQ is awesome for getting a lot of work done fast, but one thing I haven't figured out yet is how to start work with PLINQ but only let it execute for a maximum amount of time and react if it is taking too long. So, as I must admit I am still learning PLINQ, I created this extension in that ignorance. It behaves similar to ForAll<> but takes a timeout and returns false if the threads don't complete in the specified amount of time. Hope this helps someone else take PLINQ further, it definitely has helped for me ...  public static bool WaitForAll<T>(this ParallelQuery<T> query, TimeSpan timeout, Action<T> action) { Contract.Requires(query != null); Contract.Requires(action != null); var exception = (Exception)null; var cts = new CancellationTokenSource(); var forAllWithCancellation = new Action(delegate { try { query.WithCancellation(cts.Token).ForAll(action); } catch (OperationCanceledException) { // NOOP } catch (AggregateException ex) { exception = ex; } }); var mrs = new ManualResetEvent(false); var callback = new AsyncCallback(delegate { mrs.Set(); }); var result = forAllWithCancellation.BeginInvoke(callback, null); if (mrs.WaitOne(timeout)) { forAllWithCancellation.EndInvoke(result); if (exception != null) { throw exception; } return true; } else { cts.Cancel(); return false; } }

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  • Restrict Tile Map to its boundaries

    - by Farooq Arshed
    I have loaded a tmx file in cocos2dx and now I am trying to implement panning. I have successfully implemented the panning first part where the map moves. Now I want to restrict the map so it does not display the map beyond its boundary where it shows black screen. I am confused as to how to implement it. Below is my code any help would be appreciated. bool HelloWorld::init() { if ( !CCLayer::init() ) { return false; } const char* tmx= "isometric_grass_and_water.tmx"; _tileMap = new CCTMXTiledMap(); _tileMap->initWithTMXFile(tmx); this->addChild(_tileMap); this->setTouchEnabled(true); return true; } void HelloWorld::ccTouchesBegan(CCSet *touches, CCEvent *event){ CCSetIterator it; for (it=touches->begin(); it!=touches->end(); ++it){ CCTouch* touch = (CCTouch*)it.operator*(); CCLog("touches id: %d", touch->getID()); oldLoc = touch->getLocationInView(); oldLoc = CCDirector::sharedDirector()->convertToGL(oldLoc); } } void HelloWorld::ccTouchesMoved(CCSet *touches, CCEvent *event) { if (touches->count() == 1) { CCTouch* touch = (CCTouch*)( touches->anyObject() ); this->moveScreen(touch); } else if (touches->count() == 2) { this->scaleScreen(touches); } } void HelloWorld::moveScreen(CCTouch* touch) { CCPoint currentLoc = touch->getLocationInView(); currentLoc = CCDirector::sharedDirector()->convertToGL(currentLoc); CCPoint moveTo = ccpSub(oldLoc, currentLoc); moveTo = ccpMult(moveTo, -1); oldLoc = currentLoc; this->setPosition(ccpAdd(this->getPosition(), ccp(moveTo.x, moveTo.y))); }

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  • Bullet Physic: Transform body after adding

    - by Mathias Hölzl
    I would like to transform a rigidbody after adding it to the btDiscreteDynamicsWorld. When I use the CF_KINEMATIC_OBJECT flag I am able to transform it but it's static (no collision response/gravity). When I don't use the CF_KINEMATIC_OBJECT flag the transform doesn't gets applied. So how to I transform non-static objects in bullet? DemoCode: btBoxShape* colShape = new btBoxShape(btVector3(SCALING*1,SCALING*1,SCALING*1)); /// Create Dynamic Objects btTransform startTransform; startTransform.setIdentity(); btScalar mass(1.f); //rigidbody is dynamic if and only if mass is non zero, otherwise static bool isDynamic = (mass != 0.f); btVector3 localInertia(0,0,0); if (isDynamic) colShape->calculateLocalInertia(mass,localInertia); btDefaultMotionState* myMotionState = new btDefaultMotionState(); btRigidBody::btRigidBodyConstructionInfo rbInfo(mass,myMotionState,colShape,localInertia); btRigidBody* body = new btRigidBody(rbInfo); body->setCollisionFlags(body->getCollisionFlags()|btCollisionObject::CF_KINEMATIC_OBJECT); body->setActivationState(DISABLE_DEACTIVATION); m_dynamicsWorld->addRigidBody(body); startTransform.setOrigin(SCALING*btVector3( btScalar(0), btScalar(20), btScalar(0) )); body->getMotionState()->setWorldTransform(startTransform);

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  • MVC Validation with ModelState.isValid through a wizard

    - by Emmanuel TOPE
    I'm working on a small educational project on MVC 3, and I'm facing a small problem, when attempting to handle validation in my application through a wizard. I tried to get benefit from the ability of MVC3 to deliver content of a different view using the same URL, when handling an [HttpPost] method on a page. I my case,my main model's class contains about ten [Required] properties, that I would like to expose through a small wizard in 3 steps , So I want that the user may be able to enter his personal informations in the first step, then respond to some questions in the second stepp and finally receive a confirmation mail from the web application whit his credentials in the last step. I can't access the last step, because of the ModelState.isValid method that I use to handle validations, and which can't perform properly if I define some properties as [Required], but don't put them on the first view. As the replies to those questions remain in a couple of choices, I've thinked that I may use some nullable bool? for in order to avoid validation issues, but know that it's not the proper way. Are there someone who would like to help me find a way to extend my validation to those three steps ? Thanks in advance and sorry for my english, I'm not a native speaker.

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  • Random World Generation

    - by Alex Larsen
    I'm making a game like minecraft (although a different idea) but I need a random world generator for a 1024 block wide and 256 block tall map. Basically so far I have a multidimensional array for each layer of blocks (a total of 262,114 blocks). This is the code I have now: Block[,] BlocksInMap = new Block[1024, 256]; public bool IsWorldGenerated = false; Random r = new Random(); private void RunThread() { for (int BH = 0; BH <= 256; BH++) { for (int BW = 0; BW <= 1024; BW++) { Block b = new Block(); if (BH >= 192) { } BlocksInMap[BW, BH] = b; } } IsWorldGenerated = true; } public void GenWorld() { new Thread(new ThreadStart(RunThread)).Start(); } I want to make tunnels and water but the way blocks are set is like this: Block MyBlock = new Block(); MyBlock.BlockType = Block.BlockTypes.Air; How would I manage to connect blocks so the land is not a bunch of floating dirt and stone?

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  • Should a Parent with Children have a DefaultChild, or should a Child have a Default property?

    - by Stijn
    Which of the following two models makes more sense? I'm leaning towards the first one because there can only be one default child. The examples are in C# but I think it can apply to other languages too. Here DefaultChild holds one of the items in Children. class Parent { int ID { get; set; } Child DefaultChild { get; set; } IEnumerable<Child> Children { get; set; } } class Child { int ID { get; set; } } Here one of the items in Children has Default set to true while the others have it set to false. class Parent { int ID { get; set; } IEnumerable<Child> Children { get; set; } } class Child { int ID { get; set; } bool Default { get; set; } } A concrete situation: a User in our system has one or more Customers attached. When logging in, if said User has a default Customer, they are immediately working under this Customer. If they don't, they have to select a Customer to work under. While logged in, they can switch between Customers.

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  • Working with multiple interfaces on a single mock.

    - by mehfuzh
    Today , I will cover a very simple topic, which can be useful in cases we want to mock different interfaces on our expected mock object.  Our target interface is simple and it looks like:   public interface IFoo : IDisposable {     void Do(); } Now, as we can see that our target interface has implemented IDisposable and in normal cases if we have to implement it in class where language rules require use to implement that as well[no doubt about it] and whether or not there can be more complex cases, we want to ensure that rather having an extra call(..As()) or constructs to prepare it for us, we should do it in the simplest way possible. Therefore, keeping that in mind, first we create a mock of IFoo var foo = Mock.Create<IFooDispose>(); Then, as we are interested with IDisposable, we simply do: var iDisposable = foo as IDisposable;   Finally, we proceed with our existing mock code. Considering the current context, we I will check if the dispose method has invoked our mock code successfully.   bool called = false;   Mock.Arrange(() => iDisposable.Dispose()).DoInstead(() => called = true);     iDisposable.Dispose();   Assert.True(called);   Further, we assert our expectation as follows: Mock.Assert(() => iDisposable.Dispose(), Occurs.Once());   Hopefully that will help a bit and stay tuned. Enjoy!!

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  • Design guideline for saving big byte stream in c# [migrated]

    - by Praveen
    I have an application where I am receiving big byte array very fast around per 50 miliseconds. The byte array contains some information like file name etc. The data (byte array ) may come from several sources. Each time I receive the data, I have to find the file name and save the data to that file name. I need some guide lines to how should I design it so that it works efficient. Following is my code... public class DataSaver { private static Dictionary<string, FileStream> _dictFileStream; public static void SaveData(byte[] byteArray) { string fileName = GetFileNameFromArray(byteArray); FileStream fs = GetFileStream(fileName); fs.Write(byteArray, 0, byteArray.Length); } private static FileStream GetFileStream(string fileName) { FileStream fs; bool hasStream = _dictFileStream.TryGetValue(fileName, out fs); if (!hasStream) { fs = new FileStream(fileName, FileMode.Append); _dictFileStream.Add(fileName, fs); } return fs; } public static void CloseSaver() { foreach (var key in _dictFileStream.Keys) { _dictFileStream[key].Close(); } } } How can I improve this code ? I need to create a thread maybe to do the saving.

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  • improve Collision detection memory usage (blocks with bullets)

    - by Eddy
    i am making a action platform 2D game, something like Megaman. I am using XNA to make it. already made player phisics,collisions, bullets, enemies and AIs, map editor, scorolling X Y camera (about 75% of game is finished ). as i progressed i noticed that my game would be more interesting to play if bullets would be destroyed on collision with regular(stationary ) map blocks, only problem is that if i use my collision detection (each bullet with each block) sometimes it begins to lag(btw if my bullet exits the screen player can see it is removed from bullet list) So how to improve my collision detection so that memory usage would be so high? :) ( on a map 300x300 blocks for example don't think that bigger map should be made); int block = 0; int bulet= 0; bool destroy_bullet = false; while (bulet < bullets.Count) { while (block < blocks.Count) { if (bullets[bulet].P_Bul_rec.Intersects( blocks[block].rect)) {//bullets and block are Lists that holds objects of bullet and block classes //P_Bul_rec just bullet rectangle destroy_bullet = true; } block++; } if (destroy_bullet) { bullets.RemoveAt(bulet); destroy_bullet = false; } else { bulet++; } block = 0; }

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  • Unrealscript splitting a string

    - by burntsugar
    Note, this is repost from stackoverflow - I have only just discovered this site :) I need to split a string in Unrealscript, in the same way that Java's split function works. For instance - return the string "foo" as an array of char. I have tried to use the SplitString function: array SplitString( string Source, optional string Delimiter=",", optional bool bCullEmpty ) Wrapper for splitting a string into an array of strings using a single expression. as found at http://udn.epicgames.com/Three/UnrealScriptFunctions.html but it returns the entire String. simulated function wordDraw() { local String inputString; inputString = "trolls"; local string whatwillitbe; local int b; local int x; local array<String> letterArray; letterArray = SplitString(inputString,, false); for (x = 0; x < letterArray.Length; x++) { whatwillitbe = letterArray[x]; `log('it will be '@whatwillitbe); b = letterarray.Length; `log('letterarray length is '@b); `log('letter number '@x); } } Output is: b returns: 1 whatwillitbe returns: trolls However I would like b to return 6 and whatwillitbe to return each character individually. I have had a few answers proposed, however, I would still like to properly understand how the SplitString function works. For instance, if the Delimiter parameter is optional, what does the function use as a delimiter by default?

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  • Program instantly closing [migrated]

    - by Ben Clayton
    I made this program and when I compiled it there were no errors but the program just instantly closed, any answers would be appreciated. #include <iostream> //Main commands #include <string> // String commands #include <windows.h> // Sleep using namespace std; int main () { //Declaring variables float a; bool end; std::string input; end = false; // Making sure program doesn't end instantly cout << "Enter start then the number you want to count down from." << ".\n"; while (end = false){ cin >> input; cout << ".\n"; if (input.find("end") != std::string::npos) // Ends the program if user types end end = true; else if (input.find("start" || /* || is or operator*/ "restart") != std::string::npos) // Sets up the countdown timer if the user types start { cin >> a; cout << ".\n"; while (a>0){ Sleep(100); a = a - 0.1; cout << a << ".\n"; } cout << "Finished! Enter restart and then another number, or enter end to close the program" << ".\n"; } else // Tells user to start program cout << "Enter start"; } return 0; // Ends program when (end = true) }

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  • Unable to use Maya animation with scripts when imported to Unity

    - by keshk
    I am testing to import Maya animation over to Unity. I set up a simple cylinder with 2 bones and an IK handle. Made a simple animation where the cylinder bends and goes back to straight position over 24 frames. Following that, I selected everything and baked, all bones,ik,(animation by selecting all at the graph editor) and even the cylinder. I saved the scene and then select all and export as FBX with animation and bake checked. In unity imported it and at the preview able to see the animation. When I load the model into scene and play (after assigning the controller), able to see animation too. But now when I try to script it and control the animation, nothing happens. Even to test, I tried the following under the Update method. if(animation.isPlaying) Debug.Log("Animation Works"); else Debug.Log("Animation not working"); The bool doesn't even return true nor false. My animation is called "bend", thus just for try I did the following and nothing happens. animation.Play("bend"); Can please advice based on my steps, am I missing something. Do I need to add the controller or is that an unnecessary step? Did I screw up on the Maya part or the Unity part. Thanks for help.

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  • Confused about implementing Single Responsibility Principle

    - by HichemSeeSharp
    Please bear with me if the question looks not well structured. To put you in the context of my issue: I am building an application that invoices vehicles stay duration in a parking. In addition to the stay service there are some other services. Each service has its own calculation logic. Here is an illustration (please correct me if the design is wrong): public abstract class Service { public int Id { get; set; } public bool IsActivated { get; set; } public string Name { get; set } public decimal Price { get; set; } } public class VehicleService : Service { //MTM : many to many public virtual ICollection<MTMVehicleService> Vehicles { get; set; } } public class StayService : VehicleService { } public class Vehicle { public int Id { get; set; } public string ChassisNumber { get; set; } public DateTime? EntryDate { get; set; } public DateTime? DeliveryDate { get; set; } //... public virtual ICollection<MTMVehicleService> Services{ get; set; } } Now, I am focusing on the stay service as an example: I would like to know at invoicing time which class(es) would be responsible for generating the invoice item for the service and for each vehicle? This should calculate the duration cost knowing that the duration could be invoiced partially so the like is as follows: not yet invoiced stay days * stay price per day. At this moment I have InvoiceItemsGenerator do everything but I am aware that there is a better design.

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  • Best Method of function parameter validation

    - by Aglystas
    I've been dabbling with the idea of creating my own CMS for the experience and because it would be fun to run my website off my own code base. One of the decisions I keep coming back to is how best to validate incoming parameters for functions. This is mostly in reference to simple data types since object validation would be quite a bit more complex. At first I debated creating a naming convention that would contain information about what the parameters should be, (int, string, bool, etc) then I also figured I could create options to validate against. But then in every function I still need to run some sort of parameter validation that parses the parameter name to determine what the value can be then validate against it, granted this would be handled by passing the list of parameters to function but that still needs to happen and one of my goals is to remove the parameter validation from the function itself so that you can only have the actual function code that accomplishes the intended task without the additional code for validation. Is there any good way of handling this, or is it so low level that typically parameter validation is just done at the start of the function call anyway, so I should stick with doing that.

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  • StreamInsight 2.1, meet LINQ

    - by Roman Schindlauer
    Someone recently called LINQ “magic” in my hearing. I leapt to LINQ’s defense immediately. Turns out some people don’t realize “magic” is can be a pejorative term. I thought LINQ needed demystification. Here’s your best demystification resource: http://blogs.msdn.com/b/mattwar/archive/2008/11/18/linq-links.aspx. I won’t repeat much of what Matt Warren says in his excellent series, but will talk about some core ideas and how they affect the 2.1 release of StreamInsight. Let’s tell the story of a LINQ query. Compile time It begins with some code: IQueryable<Product> products = ...; var query = from p in products             where p.Name == "Widget"             select p.ProductID; foreach (int id in query) {     ... When the code is compiled, the C# compiler (among other things) de-sugars the query expression (see C# spec section 7.16): ... var query = products.Where(p => p.Name == "Widget").Select(p => p.ProductID); ... Overload resolution subsequently binds the Queryable.Where<Product> and Queryable.Select<Product, int> extension methods (see C# spec sections 7.5 and 7.6.5). After overload resolution, the compiler knows something interesting about the anonymous functions (lambda syntax) in the de-sugared code: they must be converted to expression trees, i.e.,“an object structure that represents the structure of the anonymous function itself” (see C# spec section 6.5). The conversion is equivalent to the following rewrite: ... var prm1 = Expression.Parameter(typeof(Product), "p"); var prm2 = Expression.Parameter(typeof(Product), "p"); var query = Queryable.Select<Product, int>(     Queryable.Where<Product>(         products,         Expression.Lambda<Func<Product, bool>>(Expression.Property(prm1, "Name"), prm1)),         Expression.Lambda<Func<Product, int>>(Expression.Property(prm2, "ProductID"), prm2)); ... If the “products” expression had type IEnumerable<Product>, the compiler would have chosen the Enumerable.Where and Enumerable.Select extension methods instead, in which case the anonymous functions would have been converted to delegates. At this point, we’ve reduced the LINQ query to familiar code that will compile in C# 2.0. (Note that I’m using C# snippets to illustrate transformations that occur in the compiler, not to suggest a viable compiler design!) Runtime When the above program is executed, the Queryable.Where method is invoked. It takes two arguments. The first is an IQueryable<> instance that exposes an Expression property and a Provider property. The second is an expression tree. The Queryable.Where method implementation looks something like this: public static IQueryable<T> Where<T>(this IQueryable<T> source, Expression<Func<T, bool>> predicate) {     return source.Provider.CreateQuery<T>(     Expression.Call(this method, source.Expression, Expression.Quote(predicate))); } Notice that the method is really just composing a new expression tree that calls itself with arguments derived from the source and predicate arguments. Also notice that the query object returned from the method is associated with the same provider as the source query. By invoking operator methods, we’re constructing an expression tree that describes a query. Interestingly, the compiler and operator methods are colluding to construct a query expression tree. The important takeaway is that expression trees are built in one of two ways: (1) by the compiler when it sees an anonymous function that needs to be converted to an expression tree, and; (2) by a query operator method that constructs a new queryable object with an expression tree rooted in a call to the operator method (self-referential). Next we hit the foreach block. At this point, the power of LINQ queries becomes apparent. The provider is able to determine how the query expression tree is evaluated! The code that began our story was intentionally vague about the definition of the “products” collection. Maybe it is a queryable in-memory collection of products: var products = new[]     { new Product { Name = "Widget", ProductID = 1 } }.AsQueryable(); The in-memory LINQ provider works by rewriting Queryable method calls to Enumerable method calls in the query expression tree. It then compiles the expression tree and evaluates it. It should be mentioned that the provider does not blindly rewrite all Queryable calls. It only rewrites a call when its arguments have been rewritten in a way that introduces a type mismatch, e.g. the first argument to Queryable.Where<Product> being rewritten as an expression of type IEnumerable<Product> from IQueryable<Product>. The type mismatch is triggered initially by a “leaf” expression like the one associated with the AsQueryable query: when the provider recognizes one of its own leaf expressions, it replaces the expression with the original IEnumerable<> constant expression. I like to think of this rewrite process as “type irritation” because the rewritten leaf expression is like a foreign body that triggers an immune response (further rewrites) in the tree. The technique ensures that only those portions of the expression tree constructed by a particular provider are rewritten by that provider: no type irritation, no rewrite. Let’s consider the behavior of an alternative LINQ provider. If “products” is a collection created by a LINQ to SQL provider: var products = new NorthwindDataContext().Products; the provider rewrites the expression tree as a SQL query that is then evaluated by your favorite RDBMS. The predicate may ultimately be evaluated using an index! In this example, the expression associated with the Products property is the “leaf” expression. StreamInsight 2.1 For the in-memory LINQ to Objects provider, a leaf is an in-memory collection. For LINQ to SQL, a leaf is a table or view. When defining a “process” in StreamInsight 2.1, what is a leaf? To StreamInsight a leaf is logic: an adapter, a sequence, or even a query targeting an entirely different LINQ provider! How do we represent the logic? Remember that a standing query may outlive the client that provisioned it. A reference to a sequence object in the client application is therefore not terribly useful. But if we instead represent the code constructing the sequence as an expression, we can host the sequence in the server: using (var server = Server.Connect(...)) {     var app = server.Applications["my application"];     var source = app.DefineObservable(() => Observable.Range(0, 10, Scheduler.NewThread));     var query = from i in source where i % 2 == 0 select i; } Example 1: defining a source and composing a query Let’s look in more detail at what’s happening in example 1. We first connect to the remote server and retrieve an existing app. Next, we define a simple Reactive sequence using the Observable.Range method. Notice that the call to the Range method is in the body of an anonymous function. This is important because it means the source sequence definition is in the form of an expression, rather than simply an opaque reference to an IObservable<int> object. The variation in Example 2 fails. Although it looks similar, the sequence is now a reference to an in-memory observable collection: var local = Observable.Range(0, 10, Scheduler.NewThread); var source = app.DefineObservable(() => local); // can’t serialize ‘local’! Example 2: error referencing unserializable local object The Define* methods support definitions of operator tree leaves that target the StreamInsight server. These methods all have the same basic structure. The definition argument is a lambda expression taking between 0 and 16 arguments and returning a source or sink. The method returns a proxy for the source or sink that can then be used for the usual style of LINQ query composition. The “define” methods exploit the compile-time C# feature that converts anonymous functions into translatable expression trees! Query composition exploits the runtime pattern that allows expression trees to be constructed by operators taking queryable and expression (Expression<>) arguments. The practical upshot: once you’ve Defined a source, you can compose LINQ queries in the familiar way using query expressions and operator combinators. Notably, queries can be composed using pull-sequences (LINQ to Objects IQueryable<> inputs), push sequences (Reactive IQbservable<> inputs), and temporal sequences (StreamInsight IQStreamable<> inputs). You can even construct processes that span these three domains using “bridge” method overloads (ToEnumerable, ToObservable and To*Streamable). Finally, the targeted rewrite via type irritation pattern is used to ensure that StreamInsight computations can leverage other LINQ providers as well. Consider the following example (this example depends on Interactive Extensions): var source = app.DefineEnumerable((int id) =>     EnumerableEx.Using(() =>         new NorthwindDataContext(), context =>             from p in context.Products             where p.ProductID == id             select p.ProductName)); Within the definition, StreamInsight has no reason to suspect that it ‘owns’ the Queryable.Where and Queryable.Select calls, and it can therefore defer to LINQ to SQL! Let’s use this source in the context of a StreamInsight process: var sink = app.DefineObserver(() => Observer.Create<string>(Console.WriteLine)); var query = from name in source(1).ToObservable()             where name == "Widget"             select name; using (query.Bind(sink).Run("process")) {     ... } When we run the binding, the source portion which filters on product ID and projects the product name is evaluated by SQL Server. Outside of the definition, responsibility for evaluation shifts to the StreamInsight server where we create a bridge to the Reactive Framework (using ToObservable) and evaluate an additional predicate. It’s incredibly easy to define computations that span multiple domains using these new features in StreamInsight 2.1! Regards, The StreamInsight Team

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  • On developing deep programming knowledge

    - by Robert Harvey
    Occasionally I see questions about edge cases and other weirdness on Stack Overflow that are easily answered by the likes of Jon Skeet and Eric Lippert, demonstrating a deep knowledge of the language and its many intricacies, like this one: You might think that in order to use a foreach loop, the collection you are iterating over must implement IEnumerable or IEnumerable<T>. But as it turns out, that is not actually a requirement. What is required is that the type of the collection must have a public method called GetEnumerator, and that must return some type that has a public property getter called Current and a public method MoveNext that returns a bool. If the compiler can determine that all of those requirements are met then the code is generated to use those methods. Only if those requirements are not met do we check to see if the object implements IEnumerable or IEnumerable<T>. That's cool stuff to know. I can understand why Eric knows this; he's on the compiler team, so he has to know. But what about those who demonstrate such deep knowledge who are not insiders? How do mere mortals (who are not on the C# compiler team) find out about stuff like this? Specifically, are there methods these folks use to systematically root out such knowledge, explore it and internalize it (make it their own)?

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  • Kinect Click counter function

    - by Sweta Dwivedi
    So i have the following kinect click function which will check if the hand is within the bounds then it will click with a counter . . however there is a slight problem . .the first few button clicks work fine.. but after it clicks one of the buttons it changes the game state and immediately clicks the other button without the counter reaching 200. . . Kinect click is a method in the button class. . .and each button inside a list can access the Kinect click method. . . public bool KinectClick(int x,int y) { if ((x >= position.X && x <= position.X + position.Width) && (y >= position.Y && y <= position.Y + position.Height)) { counter++; if (counter > 200) { counter = 0; return true; } } else { counter = 0; } return false; } I call to check if this property is true in the Game update method to act as a button click. . foreach(Button g_t in Game_theme) { if ((g_t.KinectClick(x_c, y_c) == true || g_t.ButtonClicked() == true) && g_t.name == "animoe") { Selected_anim = true; currentGameState = GameState.InGame; } if ((g_t.KinectClick(x_c, y_c) == true || g_t.ButtonClicked() == true) && g_t.name == "planet") { Selected_planet = true; currentGameState = GameState.InGame; }

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