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  • Are C++ meta-templates required knowledge for programmers?

    - by Robert Gould
    In my experience Meta-templates are really fun (when your compilers are compliant), and can give good performance boosts, and luckily I'm surrounded by seasoned C++ programmers that also grok meta-templates, however occasionally a new developer arrives and can't make heads or tails of some of the meta-template tricks we use (mostly Andrei Alenxandrescu stuff), for a few weeks until he gets initiated appropriately. So I was wondering what's the situation for other C++ programmers out there? Should meta-template programming be something C++ programmers should be "required" to know (excluding entry level students of course), or not? Edit: Note my question is related to production code and not little samples or prototypes

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  • calling template function without <>; type inference

    - by Oops
    Hi, if I have a function template with typename T, where the compiler can set the type by itself, I do not have to write the type explicitely when I call the function like: template < typename T > T min( T v1, T v2 ) { return ( v1 < v2 ) ? v1: v2; } int i1 = 1, i2 = 2; int i3 = min( i1, i2 ); //no explicit <type> but if I have a function template with two different typenames like... template < typename TOut, typename TIn > TOut round( TIn v ) { return (TOut)( v + 0.5 ); } double d = 1.54; int i = round<int>(d); //explicit <int> Is it true that I have to specify at least 1 typename, always? I assume the reason is because C++ can not distinguish functions between different return types, true? but if I use a void function and handover a reference, again I must not explicitely specify the return typename: template < typename TOut, typename TIn > void round( TOut & vret, TIn vin ) { vret = (TOut)(vin + 0.5); } double d = 1.54; int i; round(i, d); //no explicit <int> should the conclusion be to avoid functions with return and more prefer void functions that return via a reference when writing templates? Or is there a possibility to avoid explicitely writing the return type? something like "type inference" for templates... is "type inference" possible in C++0x? I hope I was not too unclear. many thanks in advance Oops

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  • C++: Declaration of template class member specialization (+ Doxygen bonus question!)

    - by Ziv
    When I specialize a (static) member function/constant in a template class, I'm confused as to where the declaration is meant to go. Here's an example of what I what to do - yoinked directly from IBM's reference on template specialization: template<class T> class X { public: static T v; static void f(T); }; template<class T> T X<T>::v = 0; template<class T> void X<T>::f(T arg) { v = arg; } template<> char* X<char*>::v = "Hello"; template<> void X<float>::f(float arg) { v = arg * 2; } int main() { X<char*> a, b; X<float> c; c.f(10); // X<float>::v now set to 20 } The question is, how do I divide this into header/cpp files? The generic implementation is obviously in the header, but what about the specialization? It can't go in the header file, because it's concrete, leading to multiple definition. But if it goes into the .cpp file, is code which calls X::f() aware of the specialization, or might it rely on the generic X::f()? So far I've got the specialization in the .cpp only, with no declaration in the header. I'm not having trouble compiling or even running my code (on gcc, don't remember the version at the moment), and it behaves as expected - recognizing the specialization. But A) I'm not sure this is correct, and I'd like to know what is, and B) my Doxygen documentation comes out wonky and very misleading (more on that in a moment). What seems most natural to me would be something like this, declaring the specialization in the header and defining it in the .cpp: ===XClass.hpp=== #ifndef XCLASS_HPP #define XCLASS_HPP template<class T> class X { public: static T v; static void f(T); }; template<class T> T X<T>::v = 0; template<class T> void X<T>::f(T arg) { v = arg; } /* declaration of specialized functions */ template<> char* X<char*>::v; template<> void X<float>::f(float arg); #endif ===XClass.cpp=== #include <XClass.hpp> /* concrete implementation of specialized functions */ template<> char* X<char*>::v = "Hello"; template<> void X<float>::f(float arg) { v = arg * 2; } ...but I have no idea if this is correct. The most immediate consequence of this issue, as I mentioned, is my Doxygen documentation, which doesn't seem to warm to the idea of member specialization, at least the way I'm defining it at the moment. It will always present only the first definition it finds of a function/constant, and I really need to be able to present the specializations as well. If I go so far as to re-declare the entire class, i.e. in the header: /* template declaration */ template<class T> class X { public: static T v; static void f(T); }; /* template member definition */ template<class T> T X<T>::v = 0; template<class T> void X<T>::f(T arg) { v = arg; } /* declaration of specialized CLASS (with definitions in .cpp) */ template<> class X<float> { public: static float v; static void f(float); }; then it will display the different variations of X as different classes (which is fine by me), but I don't know how to get the same effect when specializing only a few select members of the class. I don't know if this is a mistake of mine, or a limitation of Doxygen - any ideas? Thanks much, Ziv

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  • WPF Template: AdornedElement not showing!

    - by Tau Sick
    I want to add some elements to a TextBox by using a Template with the extra elements and the original TextBox inserted in the right spot. I'm trying to use the AdornedElementPlaceholder just like you would do when making a Validation.ErrorTemplate But the AdornedElement is not showing up. I have simplified the example as much as possible: <TextBox Text="Border me with my Template"> <TextBox.Template> <ControlTemplate TargetType="{x:Type TextBox}"> <Border BorderBrush="Green" BorderThickness="1"> <AdornedElementPlaceholder/> </Border> </ControlTemplate> </TextBox.Template> </TextBox> The result is just a green box around the space that should be my textbox!

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  • how to templatize partial template specializations?

    - by Kyle
    I'm not even sure what title to give this question; hopefully the code will demonstrate what I'm trying to do: #include <string> #include <list> using namespace std; template<typename A> class Alpha { public: A m_alpha_a; }; template<typename B> class Bravo { public: B m_bravo_b; }; template<> class Alpha<string> { public: string m_alpha_string; }; template<typename B> template<> class Alpha<Bravo<B> > { public: Bravo<B> m_bravo_class; // Line A }; int main() { Alpha<int> alpha_int; alpha_int.m_alpha_a= 4; Alpha<string> alpha_string; alpha_string.m_alpha_string = "hi"; Alpha<Bravo<int> > alpha_bravo_int; alpha_bravo_int.m_bravo_class.m_bravo_b = 9; }; I want to write a specialization for Alpha<A> when A is of any type Bravo<B>, but the compiler says invalid explicit specialization before ‘’ token enclosing class templates are not explicitly specialized (Referring to // Line A.) What's the correct syntax to do what I want?

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  • Get C# Templates For VS 2008 Shell

    - by Onorio Catenacci
    I've got VS 2008 Shell Integrated mode; I've got F# 2.0 on that installation. Till now this has worked fine for me because I've been hacking at F# code. Now though, I want to install Intellifactory's WebSharper. It looks like the Intellifactory templates assume that C# templates will be available because while it will create the F# portion of the solution it will not create the Web project in the solution with the complaint A problem was encountered creating the sub project 'Web Application'. The template specified cannot be found. Is there any place where I can get the C# stuff to add to this instance of VS 2008 Shell? Apologies in advance if this is a dup question but I've googled without much luck and I don't seem to find this here either. I've seen that about devenv /installvstemplates but that also fails with a message about needing to elevate privileges (which is odd since I try it under an admin user).

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  • C++ adding friend to a template class in order to typecast

    - by user1835359
    I'm currently reading "Effective C++" and there is a chapter that contains code similiar to this: template <typename T> class Num { public: Num(int n) { ... } }; template <typename T> Num<T> operator*(const Num<T>& lhs, const Num<T>& rhs) { ... } Num<int> n = 5 * Num<int>(10); The book says that this won't work (and indeed it doesn't) because you can't expect the compiler to use implicit typecasting to specialize a template. As a soluting it is suggested to use the "friend" syntax to define the function inside the class. //It works template <typename T> class Num { public: Num(int n) { ... } friend Num operator*(const Num& lhs, const Num& rhs) { ... } }; Num<int> n = 5 * Num<int>(10); And the book suggests to use this friend-declaration thing whenever I need implicit conversion to a template class type. And it all seems to make sense. But why can't I get the same example working with a common function, not an operator? template <typename T> class Num { public: Num(int n) { ... } friend void doFoo(const Num& lhs) { ... } }; doFoo(5); This time the compiler complaints that he can't find any 'doFoo' at all. And if i declare the doFoo outside the class, i get the reasonable mismatched types error. Seems like the "friend ..." part is just being ignored. So is there a problem with my understanding? What is the difference between a function and an operator in this case?

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  • Which jsPerf-test should I consider as standard for checking the performance of javascript template-engines

    - by bhargav
    I am on a search for a javascript template engine that has good performance when used in large js applications and is also very suitable for mobile applications. So I have gone through the various jsPerf-tests for these. There seems to be a lot which show different results and it is confusing to find out which is the standard test. Can some one guide me a standard jsPerf that I can refer to and that should also include following templates dust, underscore, hogan, mustache, handlebars. From what I have observed dot.js is a constant performer with good rendering speed, but is it mature enough for larger applications ? What is this "with" and "no with" that is shown in the jspref tests? Can some one explain. In all the tests I have seen popular templates like mustache, handlebars, dust, hogan,etc seems to be behind performance than other templates, so why people are using them leaving out the top performers,is it because of maturity of these template engines? Thanks in advance

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  • Is it possible to have 'sub-templates' when using MailDefinition

    - by Dan
    I am using the MailDefinition class to create html emails for my site. The only problem I am having is that there is alot of repetition in the string templates. For example the email footer along with all the associated html and css has to be repeated in each template type. Is there a way to have sub-template? or some mechanism for avoiding this repetition?

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  • "Ambiguous template specialization" problem

    - by Setien
    I'm currently porting a heap of code that has previously only been compiled with Visual Studio 2008. In this code, there's an arrangement like this: template <typename T> T convert( const char * s ) { // slow catch-all std::istringstream is( s ); T ret; is >> ret; return ret; } template <> inline int convert<int>( const char * s ) { return (int)atoi( s ); } Generally, there are a lot of specializations of the templated function with different return types that are invoked like this: int i = convert<int>( szInt ); The problem is, that these template specializations result in "Ambiguous template specialization". If it was something besides the return type that differentiated these function specializations, I could obviously just use overloads, but that's not an option. How do I solve this without having to change all the places the convert functions are called?

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  • Re render template when submit a form

    - by Agusti-N
    Hi, i've this problem: I've a view that render a template and then retrive to the user the rendered template. Yesterday i want to add a form. The problem is when i submit this form to the same url that the view render the template, i have to re render the template with previusly data and then show the errors (if they are) in the form with the new renderd data, so i have to re render all the time the previusly information. I've view a lot of examples, but ALL examples have the form in an externar html(separated) How can avoid this ?

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  • Django Template Inheritance -- Missing Images?

    - by user367817
    Howdy, I have got the following file heirarchy: project   other stuff   templates       images           images for site       app1           templates for app1       registration           login template       base.html (base for entire site)       style.css (for base.html) In the login template, I am extending 'base.html.' 'base.html' uses 'style.css' along with all of the images in the 'templates/images' directory. For some reason, none of the CSS styles or images will show up in the login template, even though I'm extending it. Does this missing image issue have something to do with screwed up "media" settings somewhere? I never understood those, but this is a major roadblock in my proof-of-concept, so any help is appreciated. Thanks!

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  • Dynamically render partial templates using mustache

    - by btakita
    Is there a way to dynamically inject partial templates (and have it work the same way in both Ruby & Javascript)? Basically, I'm trying to render different types of objects in a list. The best I can come up with is this: <div class="items"> {{#items}} <div class="item"> {{#is_message}} {{< message}} {{/is_message}} {{^is_message}} {{#is_picture}} {{< picture}} {{/is_picture}} {{^is_picture}} {{/is_picture}} {{/is_message}} </div> {{/items}} </div> For obvious reasons, I'm not super-psyched about this approach. Is there a better way? Also note that the different types of models for the views can have non-similar fields. I suppose I could always go to the lowest common denominator and have the data hash contain the html, however I would rather use the mustache templates.

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  • Django template tag basic question

    - by ninja123
    It looks like this template tag works like a charm for most people: http://blog.localkinegrinds.com/2007/09/06/digg-style-pagination-in-django/ For some reason I get this error: Caught an exception while rendering: 'is_paginated' I use this template tag in my template like so: {% load digg_paginator %} {% digg_paginator %} Where digg_paginator.py is in my app/templatetags folder and the included template context digg_paginator.html is in my app/templates folder. The queryset that needs pagination is called 'destinations'. If i just specify {% digg_paginator %}, how does it know what variable to paginate?? I feel I am missing something important here or just plain stupid :P Someone please help, or explain to me how this should be done. Thanks

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  • Template engine recommendations

    - by alex
    I'm looking for a template engine. Requirements: Runs on a JVM. Java is good; Jython, JRuby and the like, too... Can be used outside of servlets (unlike JSP) Is flexible wrt. to where the templates are stored (JSP and a lot of people require the templates to be stored in the FS). It should provide a template loading interface which one can implement or something like that Easy inclusion of parameterized templates- I really like JSP's tag fragments Good docs, nice code, etc., the usual suspects I've looked at JSP- it's nearly perfect except for the servlet and filesystem coupling, Stringtemplate- I love the template syntax, but it fails on the filesystem coupling, the documentation is lacking and template groups and stuff are confusing, GXP, TAL, etc. Ideas, thoughts? Alex

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  • Django template context not working with imported class

    - by Andy Hume
    I'm using Django's templating on appengine, and am having a problem whereby a class I'm importing from another package is not correctly being made available to the template context. Broadly speaking, this is the code. The prop1 is not available in the template in the first example below, but is in the second. MyClass is identical in both cases. This does not work: from module import MyClass context = MyClass() self.response.out.write(template.render(path, context)) This does: class MyClass(object): def __init__(self): self.prop1 = "prop1" context = MyClass() self.response.out.write(template.render(path, context)) If I log the context in the above code I get: <module.MyClass object at 0x107b1e450> when it's imported, and: <__main__.MyClass object at 0x103759390> when it's defined in the same file. Any clues as to what might cause this kind of behaviour?

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  • AppEngine and Django: including a template file

    - by PythonPower
    As the title suggests, I'm using Google App Engine and Django. I have quite a bit of identical code across my templates and would like to reduce this by including template files. So, in my main application directory I have the python handler file, the main template, and the template I want to include in my main template. I would have thought that including {% include "fileToInclude.html" %} would work on its own but that simply doesn't include anything. I assume I have to set something up, maybe using TEMPLATE_DIRS, but can't figure it out on my own. EDIT: I've tried: TEMPLATE_DIRS = (os.path.join(os.path.dirname(__file__), 'templates'), ) But to no avail. I'll try some other possibilities too.

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  • Creating readable html with django templates

    - by rileymat
    When using Django for html templating how do I create good html markup formatting. I am trying to make use of content blocks. But the content blocks show up at different levels of indentation in different templates. How do I get the content blocks to show indented like it would be if someone was to hand write the html. I am having the same problem with newlines; I can smash all the blocks together in the template. At that point the html looks better, but the templates are unmaintainable. I guess the question is how to you create pretty html markup with the django templating system?

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  • Django: common template subsections

    - by Parand
    What's a good way to handle commonly occurring subsections of templates? For example, there is a sub-header section that's used across 4 different pages. The pages are different enough to not work well with template inheritance (ie. "extends" doesn't fit well). Is "include" the recommended method here? It feels a bit heavyweight, requiring each subsection or snippet to be in its own file. Are there any performance issues in using include or is it smart about forming template from the subsections (ie. if I make extensive use of it, do I pay any penalties)? I think what I'm looking for is something like template tags, but without the programming - a simple way to create a library of html template tags I can sprinkle in other templates.

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  • need a virtual template member workaround

    - by yurib
    Hello, I need to write a program implementing the visitor design pattern. The problem is that the base visitor class is a template class. This means that BaseVisited::accept() takes a template class as a parameter and since it uses 'this' and i need 'this' to point to the correct runtime instance of the object, it also needs to be virtual. I'd like to know if there's any way around this problem. template <typename T> class BaseVisitor { public: BaseVisitor(); T visit(BaseVisited *visited); virtual ~BaseVisitor(); } class BaseVisited { BaseVisited(); template <typename T> virtual void accept(BaseVisitor<T> *visitor) { visitor->visit(this); }; // problem virtual ~BaseVisited(); }

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  • vb.net project template how can I leave the root namesapce empty

    - by Wietze Veld
    I have been tinkering with the VS 2010 template. So far I am able to create a vb.net class library project from my template. However, one small thing is bugging me. In my project template the default assembly name is the same as the default file name. I have left the root namespace empty. But when I create a new project from the template, VS 2010 automatically fills the root namespace with the same name as my assembly name. My template project (vbproj) for the assembly name and root namespace looks like this: <AssemblyName>$safeprojectname$</AssemblyName> <!-- RootNameSpace should always be empty. --> <RootNamespace></RootNamespace> But as said, when I leave this empty it is always overwritten with the assembly name. Even if I create a custom parameter with an empty string as value to replace the root namespace, it is still overridden. Any help is appreciated.

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