fold expressions, since C++17, are used to reduce the parameter packs of variadic templates over a binary operator.
Questions tagged [fold-expression]
144 questions
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vote
4 answers
Fold Expression in C++17
I'm reading "C++17 - The Complete Guide" book and I came across the example on page 107 and 108 regarding fold expression in C++17:
template
void print(First first, const Args&... args)
{
std::cout << first;
…
Ali
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1
vote
1 answer
I'm trying to create an exception class that uses a parameter pack constructor in c++
I am creating custom exception class called app_exception which is derived from runtime_exception. I want to put multiple arguments in the constructor, but I can't figure out why the code will not compile. I normally use va_start with ..., but I'm…
Arush Agarampur
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1
vote
2 answers
Improving fold function
I have implemented a simple fold function in C++ that accepts a lambda, and can fold multiple vectors at the same time at compile time. I am wondering if it could be simplified in some manner (I have provided both a recursive version and an…
lightxbulb
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1 answer
Evaluating a parameter pack
Is this the only way to evaluate a parameter pack without using folding (since it requires the use of operators)?
#include
template
void eval(Function&& f)
{
// (f(Is)...);
auto op = [&f](int…
lightxbulb
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1
vote
2 answers
Join outputs from fold/variadic expression with && operator
Function all_checked is meant to return true if all calls to parse(...) returned true, and false otherwise.
How can I link all the outputs together so that I effectively get
success = parse(args[0]) && parse(args[1]) && parse(args[2]) && ...;
Right…
Phil-ZXX
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1 answer
Variadic functions and fold expression: Fatal Error while trying to compile in Visual Studio 2017
I was reading this Q/A and some of the answers provided a possible solution for using Fold Expressions in C++17. I thought I'd try this technique within my own code.
This is what I have tried:
Some Header
#pragma once
#include
#include…
Francis Cugler
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About Logical operator using variable parameter in templates
I don't know what's happening in this code.
SimpleFunction(1,2,3) is equal to
1&&(2&&3) //1
1||(2||3) //1
SimpleFunction(1) is equal to
1&&Something //1
1||Something //1
SimpleFunction() is equal to
voidvalue (&&) //1
voidvalue (||) //0
What…
Scha
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1
vote
1 answer
Compiler error with a fold expression in enable_if_t
I have the following code, where I am using a fold expression to evaluate whether all pack parameters are convertible to the first function argument. For some reason it fails to compile on msvc when I make what seems like a very trivial…
lightxbulb
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1
vote
1 answer
Can I use a Fold Expression in this example
I want to know if it is possible to use fold expression (and how to write it) in the example below.
#include
#include
#include
#include
#include
template
std::string padFormat()
{
…
Blood-HaZaRd
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1
vote
2 answers
Are fold expressions fully supported in VS2017?
I found an interesting article and tried its code with MSVS 2017:
#include
#include
template
void for_each(const std::tuple& t, Func&& f, std::index_sequence)…
Alexey Starinsky
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1
vote
2 answers
c++17 fold expression syntatx
I have problem of make code working of fold expression in line 18 and line 23
I want make it such as have this result
"1 2 3 4"
"9 0 -1 -200"
"abc"
" world"
"Empty List"
As if the list is empty you will print "Empty List", if not, if the type is…
user3770234
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1
vote
1 answer
Can this code that expands integer parameter pack be written with just 1 function?
I have code that uses fold expressions to compare function argument against integer parmeters of class template.
Code works AFAIK, but I wonder if it is possible to do what I want without _impl helper function.
Full code(my question is if contains…
NoSenseEtAl
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0
votes
1 answer
C++ fold expressions, how to apply it with a function instead of an operator?
I have a set of messages, some of which have variable sizes but still with fixed maximum sizes. I want to get the maximum size amongst that set of messages.
template< typename... Messages >
struct BinaryMessageList
{
static constexpr size_t…
hlide
- 237
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0
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1 answer
How to expand a NTTP parameter pack with a fold expression
I have a function (bar) that takes a pack of NTTP, hax can I expand the pack using fold expression so that each element of the pack is the template parameter of another function (foo).
#include
#include
#include…
monamimani
- 273
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0
votes
1 answer
C++ varadic template function - only one instance of known parameter pack
I want to use a fold expression but the function will only ever be used with one known parameter pack.
i.e.
template
Foo fn_impl(Arg arg) {
// here, a fold expression involving Types... that returns a Foo
}
Foo fn(Arg arg) {
…
Nebular Noise
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