1,463
questions
4
votes
1
answer
154
views
Why doesn't std::array's operator[] retain the value category of the array?
I'd have expected that if an std::array is an rvalue, then calling operator[] returns an rvalue as well. But it doesn't seem to be the case (cppreference), there are no value-category overloads.
For ...
- 29.5k
0
votes
1
answer
70
views
A hash function that maintains mathematical equality (especially for sets)
I'm working on a little math-based programming language (written in Rust) that uses sets instead of types. In it, a variable or value belongs to a set of values (eg. x : {1, 2, 3} or msg : Str). The ...
- 5
1
vote
1
answer
41
views
How to implement ordered fan-in (proper message passing for my language)?
I'm the creator of https://github.com/nevalang/neva
It's a dataflow programming where you have nodes that do message passing through ports. I use go channels to implement that. However, I faced an ...
- 81
2
votes
2
answers
98
views
Why does `std::integral_constant` have a `::type` that refers to itself?
I'm reading the documentation on std::integral_constant, and apparently it includes using type that refers to itself.
template <typename T, T Value>
struct integral_constant
{
using type = ...
- 94.4k
4
votes
1
answer
130
views
Why does the standard require only input iterators for std::distance, rather than forward iterators?
I was perplexed to see that the template parameter requirement for std::distance is a LegacyInputIterator rather than a LegacyForwardIterator.
Since input-only iterators don't have the multi-pass ...
- 2,214
3
votes
1
answer
167
views
Why there is no std::numbers::sqrtpi_v?
I have a std::normal_distribution<RealType> normal_distribution and want to use its normalization constant in a constexpr. Unfortunately, I cannot use normal_distribution.stddev() * std::sqrt(2 *...
- 18.1k
3
votes
0
answers
44
views
Why is the overload for both the == and <=> operator required to overload all comparison operators? [duplicate]
I was going through this guide on operator overloading in C++.
If I try to implement all the comparison operators using the <=> operator:
friend auto operator<=>(const Some_class& lhs, ...
- 367
1
vote
3
answers
176
views
Why don't STL containers have methods for general funcitons?
I understand that there are general functions on iterators that accomplish everything you would want to do, such as std::find, std::count etc. but why don't the standard containers such as std::vector ...
- 86
3
votes
1
answer
288
views
Why `std::string_view` is not modifiable?
I start experiment with std::string_view.
It has a very ugly feature. You cannot say:
std::string_view<const char> and std::string_view<char> like the awesome std::span.
So, you cannot ...
- 2,124
1
vote
1
answer
187
views
Why did C++03 allow data members with the same name as the class?
Between the C++98 standard and the C++03 standard, an interesting change was made:
struct S {
int S;
};
This code is valid in C++03 and newer, but was ill-formed in C++98.
Specifically, [class....
- 37.8k
2
votes
1
answer
80
views
Why is initialization of inline/non-inline variables indeterminately sequenced?
int x = f();
inline int y = x;
It is unspecified whether y is zero or the value of x.
Note that x has ordered initialization and y has partially-ordered initialization (see [basic.start.dynamic] p1).
...
- 37.8k
2
votes
1
answer
126
views
Why can't C++ overload resolution deduced nested template types?
This purported duplicate explains the mechanism of why this isn't allowed and shows a corner case where it can't work, but fails to address the question of why C++ refuses to allow it in the cases ...
- 78.1k
0
votes
2
answers
109
views
Why is it illegal to call offsetof() on pointer member?
From there I know that it is illegal in C to call offsetof on a pointer, but why is it undefined behaviour? Standard implementation
#define offsetof(TYPE, MEMBER) ((size_t) &((TYPE *)0)->MEMBER)...
user20158758
0
votes
2
answers
54
views
Why is List<Subtype> able to be assigned to List<Supertype> here?
I understand that Java is generally invariant since it does not want to deal with issues of co/contra-variance.
So in general,
List<Parent> a = new ArrayList<Child>();
will require a type-...
- 1,217
5
votes
2
answers
219
views
Why are views required to be (move-)assignable?
The std::ranges::view concept in C++23 requires a view to be movable, which includes move-assignability. I understand why we want a view to be move-constructible, but why is the assignment necessary?
...
- 2,713