friend declaration declares a non-template function [duplicate]
It sounds like you want to change: friend ostream& operator << (ostream& out, const Base<T>& e); To: template<class T> friend ostream& operator << (ostream& out, const Base<T>& e);
templates
Default template argument and partial specialization
The default argument applies to the specialization — and, in fact, a specialization must accept (so to speak) the base template’s default argument(s). Attempting to specify a default in the specialization: template<class A = int, class B=double> class Base {}; template<class B=char> // … …is an error. Likewise, if we change the specialization so that … Read more
How to pass selected, named arguments to Jinja2’s include context?
Jinja2 has an extension that enables the with keyword – it won’t give you the same syntax as Django, and it may not work the way you anticipate but you could do this: {% with articles=articles_list1 %} {% include “list.html” %} {% endwith %} {% with articles=articles_list2 %} {% include “list.html” %} {% endwith %} … Read more
Template function inside template class
Write this: template <class T> template <class U> void MyClass<T>::foo() { /* … */ }
Golang template engine pipelines
There are 2 template packages, text/template and html/template. They have the same interface, but the html/template package is for generating HTML output safe against code injection, and should be used instead of text/template whenever the output is HTML. Since they have the same interface but the html/template provides some extra functionality (contextual escaping of the … Read more
Using ‘void’ template arguments in C++
The short answer is “templates are not string substitution”. void f(void) has meaning only so far as it is an alias for void f() in C++, in order to be backwards compatible with C. The first step is to use variadics, as noted elsewhere. The second step is figuring out how to map void returning … Read more
Handlebars.js if block helper ==
The easiest thing would be to add a custom if_eq helper: Handlebars.registerHelper(‘if_eq’, function(a, b, opts) { if(a == b) // Or === depending on your needs return opts.fn(this); else return opts.inverse(this); }); and then adjust your template: {{#if_eq this “some message”}} … {{else}} … {{/if_eq}} Demo: http://jsfiddle.net/ambiguous/d4adQ/ If your errors entries weren’t simple strings then … Read more
Why don’t I need to specify “typename” before a dependent type in C++20?
One of the new features in C++20 is Down with typename. In C++17, you had to provide the typename keyword in nearly all†dependent contexts to disambiguate a type from a value. But in C++20, this rule is relaxed a lot. In all contexts where you need to have a type, the typename keyword is … Read more
Can we see the templates instantiated by the C++ compiler?
Clang (https://clang.llvm.org/) can pretty-print AST of instantiated template: For your example: test.cpp template < class T> T add(T a, T b){ return a+b; } void tmp() { add<int>(10,2); } Command to pretty-print AST: $ clang++ -Xclang -ast-print -fsyntax-only test.cpp Clang-5.0/Clang 14.0 output: template <class T> T add(T a, T b) { return a + b; … Read more
How do we use void_t for SFINAE?
1. Primary Class Template When you write has_member<A>::value, the compiler looks up the name has_member and finds the primary class template, that is, this declaration: template< class , class = void > struct has_member; (In the OP, that’s written as a definition.) The template argument list <A> is compared to the template parameter list of … Read more