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• autotools: no rule to make target all

  - by Raffo

  I'm trying to port an application I'm developing to autotools. I'm not an expert in writing makefiles and it's a requisite for me to be able to use autotools. In particular, the structure of the project is the following: .. ../src/Main.cpp ../src/foo/ ../src/foo/x.cpp ../src/foo/y.cpp ../src/foo/A/k.cpp ../src/foo/A/Makefile.am ../src/foo/Makefile.am ../src/bar/ ../src/bar/z.cpp ../src/bar/w.cpp ../src/bar/Makefile.am ../inc/foo/ ../inc/bar/ ../inc/foo/A ../configure.in ../Makefile.am The root folder of the project contains a "src" folder containing the main of the program AND a number of subfolders containing the other sources of the program. The root of the project also contains an "inc" folder containing the .h files that are nothing more than the definitions of the classes in "src", thus "inc" reflects the structure of "src". I have written the following configure.in in the root: AC_INIT([PNAME], [1.0]) AC_CONFIG_SRCDIR([src/Main.cpp]) AC_CONFIG_HEADER([config.h]) AC_PROG_CXX AC_PROG_CC AC_PROG_LIBTOOL AM_INIT_AUTOMAKE([foreign]) AC_CONFIG_FILES([Makefile src/Makefile src/foo/Makefile src/foo/A/Makefile src/bar/Makefile]) AC_OUTPUT And the following is ../Makefile.am SUBDIRS = src and then in ../src where the main of the project is contained: bin_PROGRAMS = pname gsi_SOURCES = Main.cpp AM_CPPFLAGS = -I../../inc/foo\ -I../../inc/foo/A \ -I../../inc/bar/ pname_LDADD= foo/libfoo.a bar/libbar.a SUBDIRS = foo bar and in ../src/foo noinst_LIBRARIES = libfoo.a libfoo_a_SOURCES = \ x.cpp \ y.cpp AM_CPPFLAGS = \ -I../../inc/foo \ -I../../inc/foo/A \ -I../../inc/bar And the analogous in src/bar. The problem is that after calling automake and autoconf, when calling "make" the compilation fails. In particular, the program enters the directory src, then foo and creates libfoo.a, but the same fail for libbar.a, with the following error: Making all in bar make[3]: Entering directory `/user/Raffo/project/src/bar' make[3]: *** No rule to make target `all'. Stop. I have read the autotools documentation, but I'm not able to find a similar example to the one I am working on. Unfortunately I can't change the directory structure as this is a fixed requisite of the project I'm working on. I don't know if you can help me or give me any hint, but maybe you can guess the error or give me a link to a similar structured example. Thank you.

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• How Does One Make Scala Control Abstraction in Repeat Until?

  - by peter_pilgrim

  Hi I am Peter Pilgrim. I watched Martin Odersky create a control abstraction in Scala. However I can not yet seem to repeat it inside IntelliJ IDEA 9. Is it the IDE? package demo class Control { def repeatLoop ( body: = Unit ) = new Until( body ) class Until( body: = Unit ) { def until( cond: = Boolean ) { body; val value: Boolean = cond; println("value="+value) if ( value ) repeatLoop(body).until(cond) // if (cond) until(cond) } } def doTest2(): Unit = { var y: Int = 1 println("testing ... repeatUntil() control structure") repeatLoop { println("found y="+y) y = y + 1 } { until ( y < 10 ) } } } The error message reads: Information:Compilation completed with 1 error and 0 warnings Information:1 error Information:0 warnings C:\Users\Peter\IdeaProjects\HelloWord\src\demo\Control.scala Error:Error:line (57)error: Control.this.repeatLoop({ scala.this.Predef.println("found y=".+(y)); y = y.+(1) }) of type Control.this.Until does not take parameters repeatLoop { In the curried function the body can be thought to return an expression (the value of y+1) however the declaration body parameter of repeatUntil clearly says this can be ignored or not? What does the error mean?

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• Boost binding a function taking a reference

  - by Jamie Cook

  Hi all, I am having problems compiling the following snippet int temp; vector<int> origins; vector<string> originTokens = OTUtils::tokenize(buffer, ","); // buffer is a char[] array // original loop BOOST_FOREACH(string s, originTokens) { from_string(temp, s); origins.push_back(temp); } // I'd like to use this to replace the above loop std::transform(originTokens.begin(), originTokens.end(), origins.begin(), boost::bind<int>(&FromString<int>, boost::ref(temp), _1)); where the function in question is // the third parameter should be one of std::hex, std::dec or std::oct template <class T> bool FromString(T& t, const std::string& s, std::ios_base& (*f)(std::ios_base&) = std::dec) { std::istringstream iss(s); return !(iss >> f >> t).fail(); } the error I get is 1>Compiling with Intel(R) C++ 11.0.074 [IA-32]... (Intel C++ Environment) 1>C:\projects\svn\bdk\Source\deps\boost_1_42_0\boost/bind/bind.hpp(303): internal error: assertion failed: copy_default_arg_expr: rout NULL, no error (shared/edgcpfe/il.c, line 13919) 1> 1> return unwrapper<F>::unwrap(f, 0)(a[base_type::a1_], a[base_type::a2_]); 1> ^ 1> 1>icl: error #10298: problem during post processing of parallel object compilation Google is being unusually unhelpful so I hope that some one here can provide some insights.

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• Using generics in F# to create an EnumArray type

  - by Matthew

  I've created an F# class to represent an array that allocates one element for each value of a specific enum. I'm using an explicit constructor that creates a dictionary from enum values to array indices, and an Item property so that you can write expressions like: let my_array = new EnumArray<EnumType, int> my_array.[EnumType.enum_value] <- 5 However, I'm getting the following obscure compilation error at the line marked with '// FS0670' below. error FS0670: This code is not sufficiently generic. The type variable ^e when ^e : enum<int> and ^e : equality and ^e : (static member op_Explicit : ^e -> int) could not be generalized because it would escape its scope. I'm at a loss - can anyone explain this error? type EnumArray< 'e, 'v when 'e : enum<int> and 'e : equality and ^e : (static member op_Explicit : ^e -> int) > = val enum_to_int : Dictionary<'e, int> val a : 'v array new() as this = { enum_to_int = new Dictionary<'e, int>() a = Array.zeroCreate (Enum.GetValues(typeof<'e>).Length) } then for (e : obj) in Enum.GetValues(typeof<'e>) do this.enum_to_int.Add(e :?> 'e, int(e :?> 'e)) member this.Item with get (idx : 'e) : 'v = this.a.[this.enum_to_int.[idx]] // FS0670 and set (idx : 'e) (c : 'v) = this.a.[this.enum_to_int.[idx]] <- c

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• Code Coverage tool for BlackBerry

  - by Skrud

  I'm looking for a code coverage tool that I can use with a BlackBerry application. I'm using J2ME-Unit for Unit Testing and I want to see how much of my code is being covered by my tests. I've tried using Cobertura for J2ME but after days of wrestling with it I failed to get any results from it. (I believe that the instrumentation is un-done by the RAPC compilation). And despite this message, the project seems to be dead. I've looked at JInjector but the project seems very incomplete. There is little (if any) documentation and although it claims to be able to work with BlackBerry projects, I haven't seen any places where it has been used for that purpose. I've played with the project quite a bit but to no avail. I've also tried the "Coverage" view in the BlackBerry JDE, even though I use Eclipse for development. The view stays permanently blank, regardless of clicking "Refresh" and running the application from the JDE. I've looked at most of the tools on this SO thread, but they won't work with J2ME/BlackBerry projects. Has anyone had any success with any code coverage tools on the BlackBerry? If so, what tools have you used? How have you used them? If anyone has managed to get JInjector or Cobertura for J2ME to work with a BlackBerry project, what did you have to do to get it working?

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• How to use html.grid control in spark view for asp.net mvc?

  - by Anusha

  class person() { public int Id{get;set;} public string Name{get;set;} } HomeController.cs ActionResult Index() { IList list=new[]{ new person { Id = 1, Name = "Name1" }, new person { Id = 2, Name = "Name2" }, new person { Id = 3, Name = "Name3" } }; ViewData["mygrid"]=list; return view(); } Home\Index.spark !{Html.Grid[[person]]("mygrid", (column=>{ column.For(c=>c.Id); column.For(c=>c.Name); })) Am getting the error Dynamic view compilation failed..error CS1501: No overload for method 'Grid' takes '2' arguments. I have added reference to MvcContrib.dll And added following namespace in the _global.spark file <use namespace="MvcContrib.UI"/> <use namespace="MvcContrib.UI.Grid"/> <use namespace="MvcContrib.UI.Pager"/> <use namespace="MvcContrib.UI.Grid.ActionSyntax"/> <use namespace="Microsoft.Web.Mvc.Controls"/> I want to bind the data to my grid in spark view.Can anybody help.

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• LaTex: how does the include-command work?

  - by HH

  I supposed the include-command copy-pastes code in the compilation, it is wrong because the code stopped working. Please, see the middle part in the code. I only copy-pasted the code to the file and added the include-command. $ cat results/frames.tex 10.31 & 8.50 & 7.40 \\ 10.34 & 8.53 & 7.81 \\ 8.22 & 8.62 & 7.78 \\ 10.16 & 8.53 & 7.44 \\ 10.41 & 8.38 & 7.63 \\ 10.38 & 8.57 & 8.03 \\ 10.13 & 8.66 & 7.41 \\ 8.50 & 8.60 & 7.15 \\ 10.41 & 8.63 & 7.21 \\ 8.53 & 8.53 & 7.12 \\ Latex code \begin{table} \begin{tabular}{ | l | m | r |} \hline $t$ / s & $d_{1}$ / s & $d_{2}$ / s \\ $\Delta h = 0,01 s$ & $\Delta d = 0,01 s$ & $\Delta d = 0,01 s$ \\ \hline % I JUST COPIED THE CODE from here to the file, included. % It stopped working, why? \include{results/frames.tex} \hline $\pi (\frac{d_{1}}{2} - \frac{d_{2}}{2})$ & $2 \pi R h$ & $2 \pi r h$ \\ \hline \end{tabular} \end{table}

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• OleDB connection only working when debugging

  - by Francesc

  I have a C# application that connects to a named SQL Express instance on the local machine using OleDBConnection: _connection = new OleDbConnection(_strConn); _connection.Open(); _strConn is something like this: "Provider=sqloledb;Data Source=.\NAMEDINSTANCE;Initial Catalog=dbname;User Id=sa;Password=password;" If I debug the application, the connection works fine. If I run the application from Windows Explorer (the same debug compilation), I get an "OleDBException: Login timeout expired" in the Open() line after 30 seconds. The strange thing is the exception happens even if I attach the debugger to the exe. I can see that the connection string is correct and everything seems fine. I can't fine any extra information in the SQL Express error log or SQL Activity Monitor either. If it helps, here is the exception: System.Data.OleDb.OleDbException: Login timeout expired at System.Data.OleDb.OleDbConnectionInternal..ctor(OleDbConnectionString constr, OleDbConnection connection) at System.Data.OleDb.OleDbConnectionFactory.CreateConnection(DbConnectionOptions options, Object poolGroupProviderInfo, DbConnectionPool pool, DbConnection owningObject) at System.Data.ProviderBase.DbConnectionFactory.CreateNonPooledConnection(DbConnection owningConnection, DbConnectionPoolGroup poolGroup) at System.Data.ProviderBase.DbConnectionFactory.GetConnection(DbConnection owningConnection) at System.Data.ProviderBase.DbConnectionClosed.OpenConnection(DbConnection outerConnection, DbConnectionFactory connectionFactory) at System.Data.OleDb.OleDbConnection.Open() I imagine that find the issue with the information I give here might be difficult, but I don't know where else to look or what other tests to do, so any ideas on what it could be or what test I could do to find out will be really appreciated.

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• Refresher on Java classes in separate files

  - by JohnFaig

  I need a refresher on moving classes from one file into two files. My sample code is in one file called "external_class_file_main". The program runs fine and the code is shown below: Public class external_class_file_main { public static int get_a_random_number (int min, int max) { int n; n = (int)(Math.random() * (max - min +1)) + min; return (n); } public static void main(String[] args) { int r; System.out.println("Program starting..."); r = get_a_random_number (1, 5); System.out.println("random number = " + r); System.out.println("Program ending..."); } } I move the get_a_random_number class to a separate file called "external_class_file". When I do this, I get the following error: Exception in thread "main" java.lang.Error: Unresolved compilation problem: The method get_a_random_number(int, int) is undefined for the type external_class_file_main at external_class_file_main.main(external_class_file_main.java:20) The "external_class_file_main" now contains: public class external_class_file_main { public static void main(String[] args) { int r; System.out.println("Program starting..."); r = get_a_random_number (1, 5); System.out.println("random number = " + r); System.out.println("Program ending..."); } } The "external_class_file" now contains: public class external_class_file { public static int get_a_random_number (int min, int max) { int n; n = (int)(Math.random() * (max - min +1)) + min; return (n); } }

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• Constraint Validation

  - by tanuja

  I am using javax.validation.Validator and relevant classes for annotation based validation. Configuration<?> configuration = Validation.byDefaultProvider().configure(); ValidatorFactory factory = configuration.buildValidatorFactory(); Validator validator = factory.getValidator(); Set<ConstraintViolation<ValidatableObject>> constraintViolations = validator.validate(o); for (ConstraintViolation<ValidatableObject> value : constraintViolations) { List< Class< ? extends ConstraintValidator< ? extends Annotation,?>>> list = value.getConstraintDescriptor().getConstraintValidatorClasses(); } I get a compilation error stating: Type mismatch: cannot convert from List< Class< ? extends ConstraintValidator< capture#4-of ?,? to List< Class< ? extends ConstraintValidator< ? extends Annotation,? What am I missing?

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• template specialization of a auto_ptr<T>

  - by Chris Kaminski

  Maybe I'm overcomplicating things, but then again, I do sort of like clean interfaces. Let's say I want a specialization of auto_ptr for an fstream - I want a default fstream for the generic case, but allow a replacement pointer? tempate <> class auto_ptr<fstream> static fstream myfStream; fstream* ptr; public: auto_ptr() { // set ptr to &myfStream; } reset(fstream* newPtr) { // free old ptr if not the static one. ptr = newPtr }; } Would you consider something different or more elegant? And how would you keep something like the above from propagating outside this particular compilation unit? [The actual template is a boost::scoped_ptr.] EDIT: It's a contrived example. Ignore the fstream - it's about providing a default instance of object for an auto_ptr. I may not want to provide a specialized instance, but would like to keep the auto_ptr semantics for this static default object. class UserClass { public: auto_ptr<fstream> ptr; UserClass() { } } I may not provide an dynamic object at construction time - I still want it to have a meaningful default. Since I'm not looking at ownership-transfer semantics, it really shouldn't matter that my pointer class is pointing to a statically allocated object, no?

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• How can I strip Python logging calls without commenting them out?

  - by cdleary

  Today I was thinking about a Python project I wrote about a year back where I used logging pretty extensively. I remember having to comment out a lot of logging calls in inner-loop-like scenarios (the 90% code) because of the overhead (hotshot indicated it was one of my biggest bottlenecks). I wonder now if there's some canonical way to programmatically strip out logging calls in Python applications without commenting and uncommenting all the time. I'd think you could use inspection/recompilation or bytecode manipulation to do something like this and target only the code objects that are causing bottlenecks. This way, you could add a manipulator as a post-compilation step and use a centralized configuration file, like so: [Leave ERROR and above] my_module.SomeClass.method_with_lots_of_warn_calls [Leave WARN and above] my_module.SomeOtherClass.method_with_lots_of_info_calls [Leave INFO and above] my_module.SomeWeirdClass.method_with_lots_of_debug_calls Of course, you'd want to use it sparingly and probably with per-function granularity -- only for code objects that have shown logging to be a bottleneck. Anybody know of anything like this? Note: There are a few things that make this more difficult to do in a performant manner because of dynamic typing and late binding. For example, any calls to a method named debug may have to be wrapped with an if not isinstance(log, Logger). In any case, I'm assuming all of the minor details can be overcome, either by a gentleman's agreement or some run-time checking. :-)

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• How do I install websocket module for Node.js on Debian VPS?

  - by Ollie Shaw

  I currently am renting a VPS from Dreamhost which runs Debian. I am still learning command line on this OS, but fast! I have successfully installed Node.js, now I want to install the websocket module found here: https://github.com/Worlize/WebSocket-Node From the root user, I have run the following command: npm install websocket The error thrown is: [websocket v1.0.7] Native code compile failed!! On Windows, native extensions require Visual Studio and Python. On Unix, native extensions require Python, make and a C++ compiler. Start npm with --websocket:verbose to show compilation output (if any). What commands should I issue to install this websocket module and its requirements? Thanks very much! Edit: When I run sudo apt-get install gcc make I get this message: Reading package lists... Done Building dependency tree Reading state information... Done gcc is already the newest version. gcc set to manually installed. make is already the newest version. 0 upgraded, 0 newly installed, 0 to remove and 44 not upgraded. And the same error when trying to install WebSocket.

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• Overlapping template partial specialization when wanting an "override" case: how to avoid the error?

  - by user173342

  I'm dealing with a pretty simple template struct that has an enum value set by whether its 2 template parameters are the same type or not. template<typename T, typename U> struct is_same { enum { value = 0 }; }; template<typename T> struct is_same<T, T> { enum { value = 1 }; }; This is part of a library (Eigen), so I can't alter this design without breaking it. When value == 0, a static assert aborts compilation. So I have a special numerical templated class SpecialCase that can do ops with different specializations of itself. So I set up an override like this: template<typename T> struct SpecialCase { ... }; template<typename LT, typename RT> struct is_same<SpecialCase<LT>, SpecialCase<RT>> { enum { value = 1 }; }; However, this throws the error: more than one partial specialization matches the template argument list Now, I understand why. It's the case where LT == RT, which steps on the toes of is_same<T, T>. What I don't know is how to keep my SpecialCase override and get rid of the error. Is there a trick to get around this? edit: To clarify, I need all cases where LT != RT to also be considered the same (have value 1). Not just LT == RT.

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• Problem with linking in gcc

  - by chitra

  I am compiling a program in which a header file is defined in multiple places. Contents of each of the header file is different, though the variable names are the same internal members within the structures are different . Now at the linking time it is picking up from a library file which belongs to a different header not the one which is used during compilation. Due to this I get an error at link time. Since there are so many libraries with the same name I don't know which library is being picked up. I have lot of oems and other customized libraries which are part of this build. I checked out the options in gcc which talks about selecting different library files to be included. But no where I am able to see an option which talks about which libraries are being picked up the linker. If the linker is able to find more than one library file name, then which does the linker pick up is something which I am not able to understand. I don't want to specify any path, rather I want to understand how the linker is resolving the multiple libraries that it is able to locate. I tried putting -v option, but that doesn't list out the path from which the gcc picks up the library. I am using gcc on linux. Any help in this regard is highly appreciated. Regards, Chitra

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• How do I set Perl's @INC for a CGI script?

  - by pistacchio

  I have the follwing, simplest Perl CGI script: use strict; use warnings; use CGI(); use CGI::Carp qw(fatalsToBrowser); use Template; print CGI::header(); foreach(@INC) { print "$_\n"; } When called (http://[..]/cgi-bin/p.cgi) I am given the following error: Can't locate Template.pm in @INC (@INC contains: /usr/lib/perl5/site_perl/5.8.8/i386-linux-thread-multi /usr/lib/perl5/site_perl/5.8.8 /usr/lib/perl5/site_perl /usr/lib/perl5/vendor_perl/5.8.8/i386-linux-thread-multi /usr/lib/perl5/vendor_perl/5.8.8 /usr/lib/perl5/vendor_perl /usr/lib/perl5/5.8.8/i386-linux-thread-multi /usr/lib/perl5/5.8.8 .) at /home/pistacchio/webapps/htdocs/cgi-bin/p.cgi line 8. BEGIN failed--compilation aborted at /home/pistacchio/webapps/htdocs/cgi-bin/p.cgi line 8. I made sure that Template is installed and indeed when running this program from shell it works (loads Template) and outputs: Content-Type: text/html; charset=ISO-8859-1 /home/pistacchio/lib/perl5 /home/pistacchio/lib/perl5/lib/i386-linux-thread-multi /home/pistacchio/lib/perl5/lib /home/pistacchio/lib/perl5/lib/i386-linux-thread-multi /usr/lib/perl5/site_perl/5.8.8/i386-linux-thread-multi /usr/lib/perl5/site_perl/5.8.8 /usr/lib/perl5/site_perl /usr/lib/perl5/vendor_perl/5.8.8/i386-linux-thread-multi /usr/lib/perl5/vendor_perl/5.8.8 /usr/lib/perl5/vendor_perl /usr/lib/perl5/5.8.8/i386-linux-thread-multi /usr/lib/perl5/5.8.8 Template is installed in /home/pistacchio/lib/perl5/lib/i386-linux-thread-multi [pistacchio@web118 i386-linux-thread-multi]$ pwd /home/pistacchio/lib/perl5/lib/i386-linux-thread-multi [pistacchio@web118 i386-linux-thread-multi]$ ls auto perllocal.pod Template Template.pm This directory is correctly listed in env and, as previously posted, in @INC. In @INC it is shown twice, so I even tried to pop it out before calling use Template, but without result. From env: [pistacchio@web118 i386-linux-thread-multi]$ env [..] PERL5LIB=/home/pistacchio/lib/perl5:/home/pistacchio/lib/perl5/lib:/home/pistacchio/lib/perl5/lib/i386-linux-thread-multi [..] Removing use Template gets rid of the problem.

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• Any merit to a lazy-ish juxt function?

  - by NielsK

  In answering a question about a function that maps over multiple functions with the same arguments (A: juxt), I came up with a function that basically took the same form as juxt, but used map: (defn could-be-lazy-juxt [& funs] (fn [& args] (map #(apply %1 %2) funs (repeat args)))) => ((juxt inc dec str) 1) [2 0 "1"] => ((could-be-lazy-juxt inc dec str) 1) (2 0 "1") => ((juxt * / -) 6 2) [12 3 4] => ((could-be-lazy-juxt * / -) 6 2) (12 3 4) As posted in the original question, I have little clue about the laziness or performance of it, but timing in the REPL does suggest something lazy-ish is going on. => (time (apply (juxt + -) (range 1 100))) "Elapsed time: 0.097198 msecs" [4950 -4948] => (time (apply (could-be-lazy-juxt + -) (range 1 100))) "Elapsed time: 0.074558 msecs" (4950 -4948) => (time (apply (juxt + -) (range 10000000))) "Elapsed time: 1019.317913 msecs" [49999995000000 -49999995000000] => (time (apply (could-be-lazy-juxt + -) (range 10000000))) "Elapsed time: 0.070332 msecs" (49999995000000 -49999995000000) I'm sure this function is not really that quick (the print of the outcome 'feels' about as long in both). Doing a 'take x' on the function only limits the amount of functions evaluated, which probably is limited in it's applicability, and limiting the other parameters by 'take' should be just as lazy in normal juxt. Is this juxt really lazy ? Would a lazy juxt bring anything useful to the table, for instance as a compositing step between other lazy functions ? What are the performance (mem / cpu / object count / compilation) implications ? Is that why the Clojure juxt implementation is done with a reduce and returns a vector ? Edit: Somehow things can always be done simpler in Clojure. (defn could-be-lazy-juxt [& funs] (fn [& args] (map #(apply % args) funs)))

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• XSLT: use parameters in xls:sort attributes (dynamic sorting)

  - by fireeyedboy

  How do I apply a parameter to a select and order attribute in a xsl:sort element? I'ld like to do this dynamic with PHP with something like this: $xsl = new XSLTProcessor(); $xslDoc = new DOMDocument(); $xslDoc->load( $this->_xslFilePath ); $xsl->importStyleSheet( $xslDoc ); $xsl->setParameter( '', 'sortBy', 'viewCount' ); $xsl->setParameter( '', 'order', 'descending' ); But I'ld first have to now how to get this to work. I tried the following, but it gives me a 'compilation error' : 'invalid value $order for order'. $sortBy doesn't seem to do anything either: <?xml version="1.0" encoding="utf-8"?> <xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform"> <xsl:output method="xml" indent="yes"/> <xsl:param name="sortBy" select="viewCount"/> <xsl:param name="order" select="descending"/> <xsl:template match="/"> <media> <xsl:for-each select="media/medium"> <xsl:sort select="$sortBy" order="$order"/> // <someoutput> </xsl:for-each> </media> </xsl:template> </xsl:stylesheet>

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• Java ternary operator and boxing Integer/int?

  - by Markus

  I tripped across a really strange NullPointerException the other day caused by an unexpected type-cast in the ternary operator. Given this (useless exemplary) function: Integer getNumber() { return null; } I was expecting the following two code segments to be exactly identical after compilation: Integer number; if (condition) { number = getNumber(); } else { number = 0; } vs. Integer number = (condition) ? getNumber() : 0; . Turns out, if condition is true, the if-statement works fine, while the ternary opration in the second code segment throws a NullPointerException. It seems as though the ternary operation has decided to type-cast both choices to int before auto-boxing the result back into an Integer!?! In fact, if I explicitly cast the 0 to Integer, the exception goes away. In other words: Integer number = (condition) ? getNumber() : 0; is not the same as: Integer number = (condition) ? getNumber() : (Integer) 0; . So, it seems that there is a byte-code difference between the ternary operator and an equivalent if-else-statement (something I didn't expect). Which raises three questions: Why is there a difference? Is this a bug in the ternary implementation or is there a reason for the type cast? Given there is a difference, is the ternary operation more or less performant than an equivalent if-statement (I know, the difference can't be huge, but still)?

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• C# - default parameter values from previous parameter

  - by Sagar R. Kothari

  namespace HelloConsole { public class BOX { double height, length, breadth; public BOX() { } // here, I wish to pass 'h' to remaining parameters if not passed // FOLLOWING Gives compilation error. public BOX (double h, double l = h, double b = h) { Console.WriteLine ("Constructor with default parameters"); height = h; length = l; breadth = b; } } } // // BOX a = new BOX(); // default constructor. all okay here. // BOX b = new BOX(10,20,30); // all parameter passed. all okay here. // BOX c = new BOX(10); // Here, I want = length=10, breadth=10,height=10; // BOX d = new BOX(10,20); // Here, I want = length=10, breadth=20,height=10; Question is : 'To achieve above, Is 'constructor overloading' (as follows) is the only option? public BOX(double h) { height = length = breadth = h; } public BOX(double h, double l) { height = breadth = h; length = l; }

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• Duplicate Symbol Linker Error (C++ help)

  - by Vash265

  Hi. I'm learning some CSP (constraint satisfaction) theory stuff right now, and am using this library to parse XML files. I'm using Xcode as an IDE. My program compiles fine, but when it goes to link the files, I get a duplicate symbol error with the XMLParser_libxml2.hh file. My files are separated as such: A class header file that includes the XMLParser file above A class implementation file that include the class header file A main file that includes the class header file The duplicate symbol is occurring in main.o and classfile.o, but as far as I can tell, I'm not actually adding that .hh file twice. Full error: ld: duplicate symbol bool CSPXMLParser::UTF8String::to<std::basic_string<char, std::char_traits<char>, std::allocator<char> > >(std::basic_string<char, std::char_traits<char>, std::allocator<char> >&) constin /Users/vash265/CSP/Untitled/build/Untitled.build/Debug/Untitled.build/Objects-normal/x86_64/dStructFill.o and /Users/vash265/CSP/Untitled/build/Untitled.build/Debug/Untitled.build/Objects-normal/x86_64/main.o Copying the implementation of the class into the main file and taking the class implementation file out of the compilation target alleviates the error, but it's a disorganized mess this way, and I'll be adding more classes very soon (and it would be nice to have them in separate files). As I've come to understand it, this is caused by the file (XMLParser_libxml2.hh) having both the class and function definition and implementation in one file (and it seems as though this might have been necessary due to the use of templates in that 'header' file). Any ideas on how to get around sticking all my class files in my main.cpp? (I've tried ifdefs, they don't work).

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• Monotouch or Titanium for rapid application development on IPhone?

  - by Ronnie

  As a .Net developer I always dreamed for the possibility to develop with my existing skills (c#) applications for the Iphone. Both programs require a Mac and the Iphone Sdk installed. Appcelerator Titanium was the first app I tried and it is based on exposing some Iphone native api to javascript so that they can be called using that language. Monotouch starts at $399 for beeing able to deploy on the Iphone and not on the Iphone simulator while Titanium is free. Monotouch (Monodevelop) has an Ide that is currently missing in Titanium (but you can use any editor like Textmate, Aptana...) I think both program generate at the end a native precompiled app (also if I am not sure about the size of the final app on the Iphone as I think the .Net framework calls are prelilnked at compilation time in Monotouch). I am also not sure about the full coverage of all the Iphone api and features. Titanium has also the advantage to enable Android app development but as a c# developer I still find Monotouch experience more like the Visual Studio one. Which one would you choose and what are your experiences on Monotouch and Titanium?

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• Common "truisms" needing correction the most

  - by Charles Bretana

  In addition to "I never met a man I didn't like", Will Rogers had another great little ditty I've always remembered. It went: "It's not what you don't know that'll hurt you, it's what you do know that ain't so." We all know or subscribe to many IT "truisms" that mostly have a strong basis in fact, in something in our professional careers, something we learned from others, lessons learned the hard way by ourselves, or by others who came before us. Unfortuntely, as these truisms spread throughout the community, the details—why they came about and the caveats that affect when they apply—tend to not spread along with them. We all have a tendency to look for, and latch on to, small "rules" or principles that we can use to avoid doing a complete exhaustive analysis for every decision. But even though they are correct much of the time, when we sometimes misapply them, we pay a penalty that could be avoided by understooding the details behind them. For example, when user-defined functions were first introduced in SQL Server it became "common knowledge" within a year or so that they had extremely bad performance (because it required a re-compilation for each use) and should be avoided. This "trusim" still increases many database developers' aversion to using UDFs, even though Microsoft's introduction of InLine UDFs, which do not suffer from this issue at all, mitigates this issue substantially. In recent years I have run into numerous DBAs who still believe you should "never" use UDFs, because of this. What other common not-so-"trusims" do you know, which many developers believe, that are not quite as universally true as is commonly understood, and which the developer community would benefit from being better educated about? Please include why it was "true" to start off with, and under what circumstances it's not true. Limit responses to issues that are technical, where the "common" application of a "rule or principle" is in fact correct most of the time, or was correct back when it was first elucidated, but—in the edge cases, or because of not understanding the principle thoroughly, because technology has changed since it first spread, or applying the rule today without understanding the details behind the rule—can easily backfire or cause the opposite of the intended effect.

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• "variable tracking" is eating my compile time!

  - by wowus

  I have an auto-generated file which looks something like this... static void do_SomeFunc1(void* parameter) { // Do stuff. } // Continues on for another 4000 functions... void dispatch(int id, void* parameter) { switch(id) { case ::SomeClass1::id: return do_SomeFunc1(parameter); case ::SomeClass2::id: return do_SomeFunc2(parameter); // This continues for the next 4000 cases... } } When I build it like this, the build time is enormous. If I inline all the functions automagically into their respective cases using my script, the build time is cut in half. GCC 4.5.0 says ~50% of the build time is being taken up by "variable tracking" when I use -ftime-report. What does this mean and how can I speed compilation while still maintaining the superior cache locality of pulling out the functions from the switch? EDIT: Interestingly enough, the build time has exploded only on debug builds, as per the following profiling information of the whole project (which isn't just the file in question, but still a good metric; the file in question takes the most time to build): Debug: 8 minutes 50 seconds Release: 4 minutes, 25 seconds

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• How do I send floats in window messages.

  - by yngvedh

  Hi, What is the best way to send a float in a windows message using c++ casting operators? The reason I ask is that the approach which first occurred to me did not work. For the record I'm using the standard win32 function to send messages: PostWindowMessage(UINT nMsg, WPARAM wParam, LPARAM lParam) What does not work: Using static_cast<WPARAM>() does not work since WPARAM is typedef'ed to UINT_PTR and will do a numeric conversion from float to int, effectively truncating the value of the float. Using reinterpret_cast<WPARAM>() does not work since it is meant for use with pointers and fails with a compilation error. I can think of two workarounds at the moment: Using reinterpret_cast in conjunction with the address of operator: float f = 42.0f; ::PostWindowMessage(WM_SOME_MESSAGE, *reinterpret_cast<WPARAM*>(&f), 0); Using an union: union { WPARAM wParam, float f }; f = 42.0f; ::PostWindowMessage(WM_SOME_MESSAGE, wParam, 0); Which of these are preffered? Are there any other more elegant way of accomplishing this?

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