Questions tagged [parameter-pack]
171 questions
1
vote
2 answers
c++ Extract parameter type list from function pointer
Im trying to get the argument types from a function pointer
This should be the working end product
std::function::InputArgs)> func = &TestAppObject::TestMethod;
Current…
DarxDev
- 23
- 3
1
vote
3 answers
How can one construct an object from a parameter pack in a C++ template?
Given the following, how can I correctly construct an object of an unknown type from a parameter pack?
template < typename... Types >
auto foo( Types&&... types ) {
auto result = Types{ }; // How should this be done?
// Do stuff with…
cbrng
- 63
- 4
1
vote
3 answers
Can multiple parameter packs be expanded in a single expression?
I want to get a matrix from two parameter packs like the following:
template < typename T1, typename T2 > struct Multi{};
template < int ... n > struct N{};
void Print( int n ){ std::cout << n << std::endl; }
template < int ... n1, int ... n2…
Klaus
- 24,205
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1
vote
1 answer
Why does passing a parameter pack to a function with one template parameter call it multiple times?
Take this code:
template
int foo()
{
std::cout << "foo called" << std::endl;
return 10;
};
template
std::vector bar(Ts... ts)
{
std::vector vec{foo()...};
return vec;
};
int main()
{
…
JensB
- 839
- 4
- 19
1
vote
1 answer
Arrays of Objects without standard constructor using Parameter Packs
I want to fill an std::array of size N with objects without a standard constructor.
std::array myArray;
(It's std::array, 64> in my case, to be specific)
This results in the error
error: use of deleted function ...…
SpiRelli
- 88
- 6
1
vote
1 answer
default template argument and parameter pack
In a classic recursive template specialization I need one type multiple times in the class definition, e.g. for inheriting and using statement, maybe on other places also.
Example:
template < typename ... T >
class C;
template < typename FIRST,…
Klaus
- 24,205
- 7
- 58
- 113
1
vote
1 answer
Strange error while expanding parameter pack containing lambda types
I have a function which looks like foo in the following example:
template
void foo(std::function... functions) {
// does interesting things with these functions
}
Now I want to call this function…
Josef Zoller
- 921
- 2
- 8
- 24
1
vote
0 answers
How the pattern on a function template argument pack works?
Hello I have this example about variadic function templates and patterns:
int& neg(int& x){ x = -x; return x;}
void f(int& x){
std::cout << x << ", ";
}
template
void f(T& x, Args&...args){
f(…
Itachi Uchiwa
- 3,044
- 12
- 26
1
vote
1 answer
How to improve some variadic parameter pack template implementation
I have managed to make a library to help me making request to SqlLite library, specially those related with BLOB files.
The problem came because I feel that the implementation can be improved, but I do not have enought knoledge to achieve it. Any…
Pablo
- 557
- 3
- 16
1
vote
1 answer
Create C-style array form parameter pack
How can I create an array from the parameter pack?
template
void covert(Tpack ...pack){
T *arr = new T[???]; //TODO: how to get Tpack size?
// TODO: how to fill array?
}
sergej.p
- 85
- 1
- 5
1
vote
3 answers
Compare memberwise parameter packs of different lengths
template
struct type {};
template
struct are_compatibles;
template
struct are_compatibles, type>
: public…
alex-dev
- 13
- 4
1
vote
2 answers
parameter packs parameter type
I have modified the sample from https://en.cppreference.com/w/cpp/language/parameter_pack to save the string in a variable. My code
#include
void tprintf(std::string& str, const std::string& format)
{
str += format;
}
template…
Michael Schäfer
- 177
- 1
- 7
1
vote
0 answers
Undefined reference to static constexpr, if passed as function parameter pack with O0 (works with higher optimization levels)
The following code snippet can only be linked if optimization level was higher than O0:
#include
#include
void vf(std::size_t n, ...) {printf("%zu\n", n);}
template void vt(ARGS&&... args) {vf(…
wiRe
- 51
- 4
1
vote
3 answers
Expand parameter pack into tuple with tuple_cat
Godbolt link: https://godbolt.org/z/18nseEn4G
I have a std::map of various types of vectors (cast to void*) and a T& get method that gives me a reference to an element in one of the vectors in the map.
class Container {
public:
Container() {
…
Acorn
- 1,147
- 12
- 27
1
vote
1 answer
How can I implement a constexpr N-way set_union (deduplicated merge)
I have a bunch of structs holding pre-sorted std::arrays of varying number of size_ts. As a toy example, suppose we've got the following three structs:
struct F_A { static constexpr std::array bounds = { 0, 100, 200, 300 }; };
struct F_B…
stinkmeister
- 11
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