A library for C++20 that introduced std::ranges namespace, which consists of rangified algorithms from
Questions tagged [std-ranges]
379 questions
3
votes
3 answers
What is std::views::counted?
On https://en.cppreference.com/w/cpp/ranges, std::views::counted is listed in the range adaptors section. However, it is not tagged as range adaptor object.
I guess that why I can't write using the pipe operator like:
std::vector vec = {1,…
GabrielGodefroy
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3
votes
0 answers
When to use specifically the niebloid std::ranges::construct_at instead of std::construct_at?
In the situation that we have two choices of exactly the same functionality.
One is a niebloid, the other is a function.
Are there any guidelines for this in general?
std::construct_at -…
sandthorn
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3
votes
2 answers
Is it possible to make a vector of ranges in cpp20
Let's say I have a a vector>. I want to use ranges::transform in such a way that I get
vector> original_vectors;
using T = decltype(ranges::views::transform(original_vectors[0], [&](int x){
return x;
…
Aditya Jain
- 59
- 6
3
votes
1 answer
why does ranges::view_interface::size require a move constructor
I don't understand where the requirement for moving comes from. I can't find it in forward_range and sized_sentinel...
Basic example:
#include
#include
#include
class vrange: public…
serafean
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3
votes
1 answer
How to define a C++ concept for a range to a std::pair of reference wrappers?
See the code below (also here https://www.godbolt.org/z/hvnvEv1ar). The code fails to compile if I uncomment the constraint for either rng or pair. I feel like I am missing something trivial, but I can't figure out why the constraint is not…
MarkB
- 672
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- 9
3
votes
1 answer
How do I joint iterate over 2 vectors by ref?
I'm trying to iterate over 2 vectors in one go using std::views::join
Here is what I'm trying:
std::vector a {1, 2, 3}, b {4, 5, 6};
for (auto &v : {a, b} | std::views::join)
{
std::cout << v << std::endl;
}
This fails to…
Arsen Zahray
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3
votes
2 answers
ranges and temporary initializer lists
I am trying to pass what I think is a prvalue into a range adapter closure object. It won't compile unless I bind a name to the initializer list and make it an lvalue. What is happening here?
#include
using namespace std;
int…
danielNJ
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3
votes
1 answer
Is std::views::values supposed to work with std::map?
The C++20 ranges library includes some (in my opinion) amazing features. For example I really started to like the std::views::keys and std::views::values range adaptors, that simplify iterating over the keys or values of a map. While previously one…
Jakob Stark
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3
votes
1 answer
C++: Alternative to this range's view construction with same requirements?
To remove manual logic in my code, I use that construct:
std::ranges::drop_view a { std::ranges::take_view(my_range, my_range.size() -X), Y};
with X and Y values I pass at runtime.
Even though I check the algorithms, I could not find a shorter way…
Kroma
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3
votes
0 answers
Why is it undefined behavior to call `std::subrange` in a `std::string` `std::functional` lambda stored in a `std::vector`?
Consider the following code, which contains a templated std::vector type of std::function objects which consume a const & std::range and std::range::iterator. What causes the position std::ranges::iterator_t passed into the std::functional lambda to…
Robbie
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3
votes
2 answers
Is there any standard functionality for creating a flattened view of a map with a container as the mapped_type?
Is there any standard functionality to create a range/view over all pairs? The following code illustrates the view I am looking to create:
std::unordered_map> m{{"Foo", {1,2}}, {"Hello", {4,5}}};
auto view =…
MarkB
- 672
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- 9
3
votes
2 answers
can ranges split be used with a predicate?
Can this double loop be rewritten using ranges views split() ?
#include
#include
struct MyPair
{
int a;
char b;
};
vector path = {{1,'a'},{1,'z'},{2,'b'},{2,'y'}};
vector > spans;
for (int i=0; i <…
Ludovic Aubert
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3
votes
1 answer
ranges views size does not compile
#include
#include
#include
#include
#include
using namespace std;
int main()
{
vector ints = {1,2,3,4,5};
auto v = ints | views::take_while([](int i){return i<3;}) ;
for (int i :…
Ludovic Aubert
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3
votes
2 answers
Can't make my example using std::ranges::copy_if(R&& r, O result, Pred pred, Proj proj = {}) compile
I've reduced the code failing to compile to the one below:
[Demo]
#include // copy_if
#include // cout
#include // back_inserter
#include
#include
#include
struct A
{
std::string…
rturrado
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3
votes
2 answers
how to use a vector of keys to filter values from a map and produce a set using c++ ranges syntax
I am new to Eric Niebler's ranges-v3 library and I would like to solve the following simple problem:
I have a std::map containing the following:
std::map map = {
{"THIS", 1}, {"IS", 2}, {"A", 3}, {"TEST", 4}, {"WITH", 5},…
johnco3
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