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Questions tagged [variadic-templates]

Variadic templates are templates that take a variable number of parameters.

Some programming languages, like D and C++ since with the C++11 standard, support templates that take a variable number of parameters. Variadic templates are useful in a number of situations, for example, defining type-safe heterogeneous containers such as tuples and expanded metaprogramming library facilities.

http://en.wikipedia.org/wiki/Variadic_templates

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A better LOG() macro using template metaprogramming

A typical LOG() macro-based logging solution may look something like this: #define LOG(msg) \ std::cout << __FILE__ << "(" << __LINE__ << "): " << msg << std::endl This allows programmers to create data rich messages using convenient and…
Marc Eaddy
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What does six dots mean in variadic templates?

The following are some partial specializations for std::is_function from libstdc++'s : /// is_function template struct is_function : public false_type { }; template …
chys
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Non-type variadic function templates in C++11

I saw a blog post which used non-type variadic templates (currently not supported by gcc, only by clang). template struct MultiDimArray { /* ... */ }; The example in the post compiles fine but I failed to get it to…
Motti
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Quick sort at compilation time using C++11 variadic templates

I just implemented the quick sort algorithm by using C++11 variadic templates to evaluate it at compilation time. However, I encounter a performance issue when the data set is too large. #include using namespace std; template
Yuncy
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Get types of C++ function parameters

Is there a standard way to get the types of a function's arguments and pass around these types as a template parameter pack? I know that this is possible in C++ because it has been done before. I was hoping that with C++14 or the upcoming C++1z,…
Navin
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Calling a function for each variadic template argument and an array

So I have some type X: typedef ... X; and a template function f: class void f(X& x_out, const T& arg_in); and then a function g: void g(const X* x_array, size_t x_array_size); I need to write a variadic template function h that does…
Andrew Tomazos
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using declaration in variadic template

This question is inspired in the following solution to multiple inheritance overloading pseudo-ambiguity, which is a nice way to implement lambda visitors for boost::variant as proposed in this answer: I want to do something like the…
lurscher
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Lowest common ancestor in a linear lineage of types

Intro Let's suppose that we have a linear hierarchy of types like the following: Then what I want is a mechanism to return the lowest common ancestor out of an arbitrary number of types in that lineage. Attempted…
Nikos Athanasiou
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Can I implement max(A, max(B, max(C, D))) using fold expressions?

While trying to play around with C++17 fold expressions, I tried to implement max sizeof where result is maximum of the sizeof of types. I have an ugly fold version that uses variable and a lambda, but I am unable to think of a way to use fold…
NoSenseEtAl
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Are variadic constructors supposed to hide the implicitly generated ones?

Are variadic constructors supposed to hide the implicitly generated ones, i.e. the default constructor and the copy constructor? struct Foo { template Foo(Args&&... x) { std::cout << "inside the variadic…
fredoverflow
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Can parameter pack function arguments be defaulted?

This is a point about which gcc 4.9.2 and clang 3.5.2 are in sharp disagreement. The program: template int foo(int i = 0, Ts &&... args) { return i + sizeof...(Ts); } int main() { return foo(); } compiles without comment…
Mike Kinghan
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C++11 variadic std::function parameter

A function named test takes std::function<> as its parameter. template void test(std::function f) { // ... } But, if I do the following: void foo(int n) { /* ... */ } // ... test(foo); Compiler(gcc 4.6.1)…
Daniel K.
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Parameter pack expansion with lambda in C++20

Case 1: Consider the following pack expansion in lambda noexcept specifier: template auto g() { ([]() noexcept(B) {}, ...); } Clang and MSVC accept this code, but GCC rejects with: error: expansion pattern '' contains no…
康桓瑋
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Lambdas in variadic templates

Using Microsoft Visual C++ 2013 (12.0), I am encountering compile-time errors when using a lambda in a constructor in a variadic template. I have managed to boil it down as shown below (see the lines with the error comments). It appears to be a bug…
Michael Gunter
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Parameter pack must be at the end of the parameter list... When and why?

I don't get the reason for which a parameter pack must be at the end of the parameter list if the latter is bound to a class, while the constraint is relaxed if the parameter list is part of a member method declaration. In other terms, this one…
skypjack
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