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  • Why doesn't ADL find function templates?

    - by Huw Giddens
    What part of the C++ specification restricts argument dependent lookup from finding function templates in the set of associated namespaces? In other words, why won't the following compile? namespace ns { struct foo {}; template<int i> void frob(foo const&) {} } int main() { ns::foo f; frob<0>(f); }

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  • Is there any reasonable use of a function returning an anonymous struct?

    - by Akanksh
    Here is an (artificial) example of using a function that returns an anonymous struct and does "something" useful: #include <iostream> template<typename T> T* func( T* t, float a, float b ) { if(!t) { t = new T; t->a = a; t->b = b; } else { t->a += a; t->b += b; } return t; } struct { float a, b; }* foo(float a, float b) { if(a==0) return 0; return func(foo(a-1,b), a, b); } int main() { std::cout << foo(5,6)->a << std::endl; std::cout << foo(5,6)->b << std::endl; void* v = (void*)(foo(5,6)); float* f = (float*)(v); //[1] delete f now because I know struct is floats only. std::cout << f[0] << std::endl; std::cout << f[1] << std::endl; delete[] f; return 0; } There are a few points I would like to discuss: As is apparent, this code leaks, is there anyway I can NOT leak without knowing what the underlying struct definition is? see Comment [1]. I have to return a pointer to an anonymous struct so I can create an instance of the object within the templatized function func, can I do something similar without returning a pointer? I guess the most important, is there ANY (real-world) use for this at all? As the example given above leaks and is admittedly contrived. By the way, what the function foo(a,b) does is, to return a struct containing two numbers, the sum of all numbers from 1 to a and the product of a and b. EDIT: Maybe the line new T could use a boost::shared_ptr somehow to avoid leaks, but I haven't tried that. Would that work?

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  • Can I append to a preprocessor macro?

    - by JCSalomon
    Is there any way in standard C—or with GNU extensions—to append stuff to a macro definition? E.g., given a macro defined as #define quux_list X(foo) X(bar) can I append X(bas) so that it now expands as if I’d defined it #define quux_list X(foo) X(bar) X(bas)? I’m playing with discriminated/tagged unions along these lines: struct quux_foo { int x; }; struct quux_bar { char *s; }; struct quux_bas { void *p; }; enum quux_type {quux_foo, quux_bar, quux_bas}; struct quux { enum quux_type type; union { struct quux_foo foo; struct quux_bar bar; struct quux_bas bas; } t; }; I figure this is a good place for the X-macro. If I define a macro #define quux_table X(foo) X(bar) X(bas) the enumeration & structure can be defined thus, and never get out of sync: #define X(t) quux_ ## t, enum quux_type {quux_table}; #undef X #define X(t) struct quux_ ## t t; struct quux { enum quux_type type; union {quux_table} t; }; #undef X Of course, the quux_* structures can get out of sync, so I’d like to do something like this, only legally: struct quux_foo { int x; }; #define quux_table quux_table X(foo) struct quux_bar { char *s; }; #define quux_table quux_table X(bar) struct quux_bas { void *p; }; #define quux_table quux_table X(bas) (Well, what I really want to be able to do is something like member_struct(quux, foo) { int x; }; but I’m well aware that macros cannot be (re)defined from within macros.) Anyhow, that’s my motivating example. Is there a way to accomplish this? Boost.Preprocessor examples are fine, if you can show me how to make the X-macro technique work with that library.

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  • SML/NJ incomplete match

    - by dimvar
    I wonder how people handle nonexhaustive match warnings in the SML/NJ compiler. For example, I may define a datatype datatype DT = FOO of int | BAR of string and then have a function that I know only takes FOOs fun baz (FOO n) = n + 1 The compiler will give a warning stdIn:1.5-1.24 Warning: match nonexhaustive FOO n = ... val baz = fn : DT - int I don't wanna see warnings for incomplete matches I did on purpose, because then I have to scan through the output to find a warning that might actually be a bug. I can write the function like this fun baz (FOO n) = n + 1 | baz _ = raise Fail "baz" but this clutters the code. What do people usually do in this situation?

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  • Pointer to auto_ptr instead of a classical double pointer

    - by Pin
    Hello. I'm quite new to smart pointers and was trying to refactor some existing code to use auto_ptr. The question I have is about double pointers and their auto_ptr equivalent, if that makes sense. I have a function that accepts a double pointer as its parameter and the function allocates resources for it: void foo ( Image** img ) { ... *img = new Image(); ...} This function is then used like this: Image* img = NULL; foo ( &img ); ... delete img; I want to use auto_ptr to avoid having to call delete explicitly. Is the following correct? void foo ( auto_ptr<Image>* img ); and then auto_ptr<Image> img = NULL; foo ( &img ); Thanks.

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  • java xml pretty printing - preserve empty elements and white pace

    - by javamonkey79
    Basically, I am looking for a java library that will take this: <foo><bar> </bar><baz>yadda</baz></foo> And pretty print it to this: <?xml version="1.0" encoding="UTF-8"?> <foo> <bar> </bar> <baz>yadda</baz> </foo> e.g. preserving whitespace AND blank elements The closest I have got was with dom4j like so: OutputFormat format = OutputFormat.createPrettyPrint(); format.setTrimText( false ); However, this does not honor the whitespace unless the element contains other character data. I'm not opposed to writing something on my own, but I would think this has already been done, why reinvent the wheel?

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  • bash: function + source + declare = boom

    - by Chen Levy
    Here is a problem: In my bash scripts I want to source several file with some checks, so I have: if [ -r foo ] ; then source foo else logger -t $0 -p crit "unable to source foo" exit 1 fi if [ -r bar ] ; then source bar else logger -t $0 -p crit "unable to source bar" exit 1 fi # ... etc ... Naively I tried to create a function that do: function save_source() { if [ -r $1 ] ; then source $1 else logger -t $0 -p crit "unable to source $1" exit 1 fi } safe_source foo safe_source bar # ... etc ... But there is a snag there. If one of the files foo, bar, etc. have a global such as -- declare GLOBAL_VAR=42 -- it will effectively become: function save_source() { # ... declare GLOBAL_VAR=42 # ... } thus a global variable becomes local. The question: An alias in bash seems too weak for this, so must I unroll the above function, and repeat myself, or is there a more elegant approach? ... and yes, I agree that Python, Perl, Ruby would make my file easier, but when working with legacy system, one doesn't always have the privilege of choosing the best tool.

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  • How can I specifiy JUnit test dependencies?

    - by Egon Willighagen
    Our toolkit has over 15000 JUnit tests, and many tests are known to fail if some other test fails. For example, if the method X.foo() uses functionality from Y.foo() and YTest.testFoo() fails, then XTest.testFoo() will fail too. Obviously, XTest.testFoo() can also fail because of problems specific to X.foo(). While this is fine and I still want both tests run, it would be nice if one could annotate a test dependency with XTest.testFoo() pointing to YTest.testFoo(). This way, one could immediately see what functionality used by X.foo() is also failing, and what not. Is there such annotation available in JUnit or elsewhere? Something like: public YTests { @Test @DependsOn(method=org.example.tests.YTest#testFoo) public void testFoo() { // Assert.something(); } }

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  • Avoiding improper std::string initialization with NULL const char* using g++

    - by pachanga
    A there any g++ options which can detect improper initialization of std::string with NULL const char*? I was in the process of turning some int fields into std::string ones, i.e: struct Foo { int id; Foo() : id(0) {} }; ...turned into: struct Foo { std::string id; Foo() : id(0) {} //oooops! }; I completely overlooked bad 'id' initialization with 0 and g++ gave me no warnings at all. This error was detected in the run time(std::string constructor threw an exception) but I'd really like to detect such stuff in the compile time. Is there any way?

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  • ANDing javascript objects together

    - by Jonas
    I ran across this chunk of code (modified) in our application, and am confused to how it works: function someObject() { this.someProperty = {}; this.foo = { bar: { baz: function() { return "Huh?" } } }; this.getValue = function() { return (this.someProperty && this.foo.bar && this.foo.bar.baz && this.foo.bar.baz()) || null; } } function test() { var o = new someObject(); var val = o.getValue(); alert(val); } when you call the test() function, the text "Huh?" is alerted. I'm not sure how the result of getValue is returning that, I would've thought doing A && B && C && D would have returned true, rather than the value of D.

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  • By-Name-Parameters for Constructors

    - by hotzen
    Hello, coming from my other question is there a way to get by-name-parameters for constructors working? I need a way to provide a code-block which is executed on-demand/lazy/by-name inside an object and this code-block must be able to access the class-methods as if the code-block were part of the class. Following Testcase fails: package test class ByNameCons(code: => Unit) { def exec() = { println("pre-code") code println("post-code") } def meth() = println("method") def exec2(code2: => Unit) = { println("pre-code") code2 println("post-code") } } object ByNameCons { def main(args: Array[String]): Unit = { val tst = new ByNameCons { println("foo") meth() // knows meth() as code is part of ByNameCons } tst.exec() // ByName fails (executed right as constructor) println("--------") tst.exec2 { // ByName works println("foo") //meth() // does not know meth() as code is NOT part of ByNameCons } } } Output: foo method pre-code post-code -------- pre-code foo post-code

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  • Go Channels in Ruby

    - by Julius Eckert
    In the Go programming language, you can send Messages around using a construct called "Channels". http://golang.org/doc/effective_go.html#channels I would love to use something like that in Ruby, especially for IPC. Pseudocode of what I want: channel = Channel.new fork do 3.times{ channel.send("foo ") } exit! end Thread.new do 3.times{ channel.send("bar ") } end loop do print channel.recv end # ~> bar foo foo bar bar foo Is there any construct, library or equivalent for Ruby which works like that ? If not: What is the best way to build such an abstraction?

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  • C#: Exception to throw when a certain type was expected

    - by cbp
    I know this sort of code is not best practice, but nevertheless in certain situations I find it is a simpler solution: if (obj.Foo is Xxxx) { // Do something } else if (obj.Foo is Yyyy) { // Do something } else { throw new Exception("Type " + obj.Foo.GetType() + " is not handled."); } Anyone know if there is a built-in exception I can throw in this case?

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  • How to unit test this simple ASP.NET MVC controller

    - by Frank Schwieterman
    Lets say I have a simple controller for ASP.NET MVC I want to test. I want to test that a controller action (Foo, in this case) simply returns a link to another action (Bar, in this case). How would you test this? (either the first or second link) My implementation has the same link twice. One passes the url throw ViewData[]. This seems more testable to me, as I can check the ViewData collection returned from Foo(). Even this way though, I don't know how to validate the url itself without making dependencies on routing. The controller: public class TestController : Controller { public ActionResult Foo() { ViewData["Link2"] = Url.Action("Bar"); return View("Foo"); } public ActionResult Bar() { return View("Bar"); } } the "Foo" view: <%@ Page Title="" Language="C#" Inherits="System.Web.Mvc.ViewPage" MasterPageFile="~/Views/Shared/Site.Master"%> <asp:Content ContentPlaceHolderID="MainContent" runat="server"> <%= Html.ActionLink("link 1", "Bar") %> <a href="<%= ViewData["Link2"]%>">link 2</a> </asp:Content>

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  • Idiomatic Python: 'times' loop

    - by perimosocordiae
    Say I have a function foo that I want to call n times. In Ruby, I would write: n.times { foo } In Python, I could write: for _ in xrange(n): foo() But that seems like a hacky way of doing things. My question: Is there an idiomatic way of doing this in Python?

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  • createChildren Called Before Component's MXML Bracket Logic Is Evaluated

    - by Nalandial
    I have the following MXML: <mx:Script> var someBoolean:Boolean = determineSomeCondition(); </mx:Script> .... <foo:MyComponent somePropertyExpectingIDataRenderer="{ someBoolean ? new Component1ThatImplementsIDataRenderer() : new Component2ThatImplementsIDataRenderer() }"> </foo:MyComponent> I have also overridden the createChildren() function: override protected function createChildren():void { super.createChildren(); //do something with somePropertyExpectingIDataRenderer } My problem is: createChildren() is being called before the squiggly bracket logic is being evaluated, so in createChildren(), somePropertyExpectingIDataRenderer is null. However if I pass the component via MXML like this: <foo:MyComponent> <bar:somePropertyExpectingIDataRenderer> <baz:Component1ThatImplementsIDataRenderer/> </bar:somePropertyExpectingIDataRenderer> </foo:MyComponent> Then when createChildren() is called, that same property isn't null. Is this supposed to happen and if so, what other workarounds should I consider?

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  • Referencing Environment Variables in web.xml

    - by Udi Bar-On
    I'm pre-packaging a JSP web-app that relies on some file path settings found within web.xml. These settings are unknown at packaging time, because they reference a path the customer will set when deploying the entire application (of which the web-app is a management interface). It seems that the easiest way to avoid tokens and file modifications in my installer script, is to ask the user for an install location, set this location as an environment variable (e.g JAVA_HOME), and have web.xml always reference that variable. Is there a way to reference an environment variable value from within web.xml? Google searches lead to the J2EE method of SETTING environment variables from ejb xml files. This is not what I'm looking for. Thanks Udi

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  • How do I replace custom "tags" in a string?

    - by Fake Code Monkey Rashid
    Given the following: $foo = "Yo [user Cobb] I heard you like dreams so I put a dream in yo dream in yo dream so you can dream while you dream while you dream." I'd like to do this: $foo = bar($foo); echo $foo; And get something like this: Yo Cobb I heard you like dreams so I put a dream in yo dream in yo dream so you can dream while you dream while you dream. I'm unsure of how the bar function should work. I think this is doable with regular expressions but I personally find those hard to understand. Using the strpos function is another method but I wonder if there is a better solution. Pseudocode is fine but actual code will be appreciated.

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  • How can I use functools.partial on multiple methods on an object, and freeze parameters out of order

    - by Joseph Garvin
    I find functools.partial to be extremely useful, but I would like to be able to freeze arguments out of order (the argument you want to freeze is not always the first one) and I'd like to be able to apply it to several methods on a class at once, to make a proxy object that has the same methods as the underlying object except with some of its methods parameter being frozen (think of it as generalizing partial to apply to classes). I've managed to scrap together a version of functools.partial called 'bind' that lets me specify parameters out of order by passing them by keyword argument. That part works: >>> def foo(x, y): ... print x, y ... >>> bar = bind(foo, y=3) >>> bar(2) 2 3 But my proxy class does not work, and I'm not sure why: >>> class Foo(object): ... def bar(self, x, y): ... print x, y ... >>> a = Foo() >>> b = PureProxy(a, bar=bind(Foo.bar, y=3)) >>> b.bar(2) Traceback (most recent call last): File "<stdin>", line 1, in <module> TypeError: bar() takes exactly 3 arguments (2 given) I'm probably doing this all sorts of wrong because I'm just going by what I've pieced together from random documentation, blogs, and running dir() on all the pieces. Suggestions both on how to make this work and better ways to implement it would be appreciated ;) One detail I'm unsure about is how this should all interact with descriptors. Code follows. from types import MethodType class PureProxy(object): def __init__(self, underlying, **substitutions): self.underlying = underlying for name in substitutions: subst_attr = substitutions[name] if hasattr(subst_attr, "underlying"): setattr(self, name, MethodType(subst_attr, self, PureProxy)) def __getattribute__(self, name): return getattr(object.__getattribute__(self, "underlying"), name) def bind(f, *args, **kwargs): """ Lets you freeze arguments of a function be certain values. Unlike functools.partial, you can freeze arguments by name, which has the bonus of letting you freeze them out of order. args will be treated just like partial, but kwargs will properly take into account if you are specifying a regular argument by name. """ argspec = inspect.getargspec(f) argdict = copy(kwargs) if hasattr(f, "im_func"): f = f.im_func args_idx = 0 for arg in argspec.args: if args_idx >= len(args): break argdict[arg] = args[args_idx] args_idx += 1 num_plugged = args_idx def new_func(*inner_args, **inner_kwargs): args_idx = 0 for arg in argspec.args[num_plugged:]: if arg in argdict: continue if args_idx >= len(inner_args): # We can't raise an error here because some remaining arguments # may have been passed in by keyword. break argdict[arg] = inner_args[args_idx] args_idx += 1 f(**dict(argdict, **inner_kwargs)) new_func.underlying = f return new_func

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  • mySQL Efficiency Issue - How to find the right balance of normalization...?

    - by Foo
    I'm fairly new to working with relational databases, but have read a few books and know the basics of good design. I'm facing a design decision, and I'm not sure how to continue. Here's a very over simplified version of what I'm building: People can rate photos 1-5, and I need to display the average votes on the picture while keeping track of the individual votes. For example, 12 people voted 1, 7 people voted 2, etc. etc. The normalization freak of me initially designed the table structure like this: Table pictures id* | picture | userID | Table ratings id* | pictureID | userID | rating With all the foreign key constraints and everything set as they shoudl be. Every time someone rates a picture, I just insert a new record into ratings and be done with it. To find the average rating of a picture, I'd just run something like this: SELECT AVG(rating) FROM ratings WHERE pictureID = '5' GROUP by pictureID Having it setup this way lets me run my fancy statistics to. I can easily find who rated a certain picture a 3, and what not. Now I'm thinking if there's a crapload of ratings (which is very possible in what I'm really designing), finding the average will became very expensive and painful. Using a non-normalized version would seem to be more efficient. e.g.: Table picture id | picture | userID | ratingOne | ratingTwo | ratingThree | ratingFour | ratingFive To calculate the average, I'd just have to select a single row. It seems so much more efficient, but so much more uglier. Can someone point me in the right direction of what to do? My initial research shows that I have to "find the right balance", but how do I go about finding that balance? Any articles or additional reading information would be appreciated as well. Thanks.

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  • Export to RSS Feed

    - by citronas
    I'm looking for class that can generate RSS feeds. I'm thinking of a usage like this. RssClass foo = new RssClass(); foo.addEntry("title", URL); foo.Export("myexportpath.rss"); Has anybody seen such a class available for free usage?

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  • Strong Signing, and Updating A Referencing Assembly

    - by Alan
    Hi, I have two, third party assemblies: Foo.dll and ReferencesFoo.dll As noted, ReferencesFoo.dll is an assembly that has a reference to Foo.dll For my application, I need to resign these assemblies. I use ildasm/ilasm in combination along with a signing key to resign them, however, ReferencesFoo.dll still contains (in it's manifest?) the reference to the Foo.dll old public key and public key token. So, how do I sign both dll's with my key, and update the references in ReferencesFoo.dll without getting the source code and recompiling?

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