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cpp_utility/0eQsx6ip1DwJpli1_257_0.txt | Delete | |
cpp_utility/cpp_classes_0_0.txt | ##### [ cppreference.com ](/)
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cpp_utility/constexprarraysize_66_0.txt | #define ARRAY_SIZE(a) type_size( \
type<std::remove_cvref_t<decltype(a)>>) | |
cpp_utility/constexprarraysize_99_0.txt | Getting to the point where we can access the size of a range as a constant
expression - whether that size is part of the type (as it is for C arrays and
` std::array ` ) or a variable part of a ` constexpr ` object (as it would be
for a wide variety of ranges) - would require multiple language changes. | |
cpp_utility/76362_61_0.txt | [
](/dyumin) | |
cpp_utility/constexprarraysize_55_0.txt | template <typename T> struct type_t { using type = T; };
template <typename T> inline constexpr type_t<T> type{}; | |
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cpp_utility/76362_18_0.txt | * [ The ReadME Project GitHub community articles ](https://github.com/readme) | |
cpp_utility/0eQsx6ip1DwJpli1_181_0.txt |  | |
cpp_utility/constexprarraysize_110_0.txt | [ c++ ](/tags/c/) [ c++20 ](/tags/c-20/) [ ranges ](/tags/ranges/) [ optional
](/tags/optional/) [ concepts ](/tags/concepts/) [ c++17 ](/tags/c-17/) [
spaceship ](/tags/spaceship/) [ c++23 ](/tags/c-23/) [ span ](/tags/span/) [ d
](/tags/d/) | |
cpp_utility/0eQsx6ip1DwJpli1_236_0.txt | Copy link | |
cpp_utility/76362_34_0.txt | Query | |
cpp_utility/CanIconstexpranstdar_34_0.txt | Profile photo for Fr
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Why can't std::map be constexpr?
It can. | |
cpp_utility/cpp_tag_2_1.txt | parison "cpp/utility")
[ three_way_comparable three_way_comparable_with
](/w/cpp/utility/compare/three_way_comparable "cpp/utility/compare/three way
comparable") (C++20) (C++20)
[ strong_ordering ](/w/cpp/utility/compare/strong_ordering
"cpp/utility/compare/strong ordering") (C++20)
[ weak_ordering ](/w/cpp/u... | |
cpp_utility/0eQsx6ip1DwJpli1_109_0.txt | David Krauss < [ pot...@gmail.com ]() > writes: | |
cpp_utility/76362_3_0.txt | [ ](https://github.com/) | |
cpp_utility/constexprarraysize_45_0.txt | std::vector<int> v5 = {1, 2, 3, 4, 5};
f(std::span<int, 5>(v5)); // well-formed | |
cpp_utility/0eQsx6ip1DwJpli1_139_0.txt | ### Gabriel Dos Reis | |
cpp_utility/CanIconstexpranstdar_48_0.txt | You can take control of HTML5, CSS3, and JavaScript in a completely visual canvas — and let Webflow translate your design into clean, semantic code that’s ready to publish to the web, or hand off | |
cpp_utility/0eQsx6ip1DwJpli1_0_0.txt | [
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cpp_utility/0eQsx6ip1DwJpli1_123_0.txt | Sign in to forward | |
cpp_utility/76362_122_0.txt | [ 
](/shafik) [
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](/EugeneZelenko) | |
cpp_utility/0eQsx6ip1DwJpli1_284_0.txt | Show original message | |
cpp_utility/constexprarraysize_79_0.txt | constexpr std::array<int, 5> some_const_array = {1, 2, 3, 4, 5};
constexpr std::span<int> dynamic_span = some_const_array; // ok
static_assert(dynamic_span.size() == 5); // ok | |
cpp_utility/constexprarraysize_18_0.txt | template <typename T, size_t N>
constexpr size_t array_size(T (&)[N]) {
return N;
} | |
cpp_utility/76362_19_0.txt | Repositories | |
cpp_utility/cpp_classes_4_1.txt | nt ](/w/cpp/utility/breakpoint "cpp/utility/breakpoint") (C++26)
[ Three-way comparison ](/w/cpp/utility#Three-way_comparison "cpp/utility")
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cpp_utility/0eQsx6ip1DwJpli1_285_0.txt | Either email addresses are anonymous for this group or you need the view
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cpp_utility/cpp_classes_1_0.txt | ##### [ cppreference.com ](/)
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cpp_utility/76362_57_0.txt | [ dyumin ](/dyumin) opened this issue Dec 25, 2023 · 3 comments | |
cpp_utility/constexprarraysize_85_0.txt | std::vector<std::span<int, 5>> bunch_of_spans;
bunch_of_spans.push_back(c_array);
bunch_of_spans.push_back(cpp_array);
bunch_of_spans.push_back(dynamic_span); | |
cpp_utility/0eQsx6ip1DwJpli1_171_0.txt | Show original message | |
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cpp_utility/0eQsx6ip1DwJpli1_175_0.txt | > On 10/13/13 4:55 PM, Gabriel Dos Reis wrote:
>
> | |
cpp_utility/constexprarraysize_97_0.txt |
### Recap __ | |
cpp_utility/0eQsx6ip1DwJpli1_124_0.txt | Delete | |
cpp_utility/constexprarraysize_62_0.txt | // this is fine, s.size() is a constant expression
static_assert(s.size() == 5); | |
cpp_utility/76362_120_0.txt | No branches or pull requests | |
cpp_utility/constexprarraysize_101_0.txt | __ [ c++ ](/tags/c/) [ constexpr ](/tags/constexpr/) [ span ](/tags/span/) | |
cpp_utility/0eQsx6ip1DwJpli1_215_0.txt | to std-dis...@isocpp.org, thomas....@gmail.com | |
cpp_utility/constexprarraysize_19_0.txt |
This beats the C macro approach both by not being a macro and by not giving
bogus answers for ` vector<T> ` . But it has possibly-surprising limitations: | |
cpp_utility/76362_102_0.txt | Copy link | |
cpp_utility/CanIconstexpranstdar_44_0.txt | If your array is owned by an std::unique_ptr then the std::unique_ptr has ownership, and you should not be using another smart pointer to provide access to the object. | |
cpp_utility/0eQsx6ip1DwJpli1_147_0.txt | You do not have permission to delete messages in this group | |
cpp_utility/0eQsx6ip1DwJpli1_170_0.txt | Sign in to report message | |
cpp_utility/0eQsx6ip1DwJpli1_67_0.txt | Unfortunately, during the Chicago meeting it was decided that a
conforming implementation is no longer permitted to add constexpr to
other functions, see | |
cpp_utility/CanIconstexpranstdar_11_0.txt | Profile photo for Kurt Guntheroth
Kurt Guntheroth
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Why can't std::map be constexpr?
std::map cannot be constexpr because the compiler cannot evaluate std::map memb... | |
cpp_utility/0eQsx6ip1DwJpli1_265_0.txt | Le samedi 12 octobre 2013 17:05:21 UTC+2, Daniel Krügler a écrit : | |
cpp_utility/76362_69_0.txt | int main()
{
return Array[3];
} | |
cpp_utility/0eQsx6ip1DwJpli1_188_0.txt | Sign in to forward | |
cpp_utility/constexprarraysize_35_0.txt | C++20 will have a new type ` std::span ` ( [ cppref
](https://en.cppreference.com/w/cpp/container/span) , I’ve written about `
span ` before [ here ](/c++/2018/12/03/span-best-span/) ), which is a
contiguous view on ` T ` . ` span ` comes in two flavors: dynamic extent and
fixed extent. Roughly speaking: | |
cpp_utility/constexprarraysize_78_0.txt |
Would this even be a sufficient rule? Still no! It still wouldn’t work for the
example I showed earlier: | |
cpp_utility/CanIconstexpranstdar_28_0.txt | Sponsored by JetBrains
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I have been programming since grade schoolUpvoted by
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cpp_utility/0eQsx6ip1DwJpli1_245_0.txt | >
>
>
>
> N3691 is supposed to be identical to N3690, other than the cover sheet. If
> it's not, that's unintended, and you should let the project editor know.
> (N3690 is the Committee Draft, N3691 is the Working Draft). In this
> instance, I don't see what you're referring to: in both documents, page 764
> contains a... | |
cpp_utility/0eQsx6ip1DwJpli1_46_0.txt | return compile_time_sort_imp ( seq , idx );
} | |
cpp_utility/constexprarraysize_36_0.txt | // fixed-extent: always has size Extent, only needs
// to store a single pointer
template <typename T, size_t Extent = dynamic_extent>
struct span {
T* ptr; | |
cpp_utility/0eQsx6ip1DwJpli1_154_0.txt | David Krauss < [ pot...@gmail.com ]() > writes: | |
cpp_utility/constexprarraysize_63_0.txt | // ... but this still wouldn't work!
std::span<int, 5> fixed = s; | |
cpp_utility/0eQsx6ip1DwJpli1_114_0.txt | A decade later, the world looks very different; it is hard to live with
history, but that is the price we pay for progress. | |
cpp_utility/cpp_tag_2_0.txt | ##### [ cppreference.com ](/)
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cpp_utility/0eQsx6ip1DwJpli1_160_0.txt | unread, | |
cpp_utility/0eQsx6ip1DwJpli1_263_0.txt | Either email addresses are anonymous for this group or you need the view
member email addresses permission to view the original message | |
cpp_utility/0eQsx6ip1DwJpli1_41_0.txt | constepxr std :: array < int , 4 > sorted_indices = compile_time_sort
< 4 , 6 , 1 , 9 >(); // don't compile | |
cpp_utility/cpp_classes_0_3.txt | ---|---|---
### [ [ edit ](/mwiki/index.php?title=cpp/utility/pair&action=edit§ion=2
"Edit section: Member types") ] Member types
Member type | Definition
---|---
` first_type ` | ` T1 `
` second_type ` | ` T2 `
### [ [ edit ](/mwiki/index.php?title=cpp/utility/pair&action=edit§ion=3
"E... | |
cpp_utility/76362_85_0.txt | [ https://godbolt.org/z/M5YG1739x ](https://godbolt.org/z/M5YG1739x) | |
cpp_utility/0eQsx6ip1DwJpli1_71_0.txt |  | |
cpp_utility/76362_29_0.txt | Include my email address so I can be contacted | |
cpp_utility/0eQsx6ip1DwJpli1_76_0.txt | Sign in to reply to author | |
cpp_utility/0eQsx6ip1DwJpli1_83_0.txt | Sign in to report message | |
cpp_utility/constexprarraysize_89_0.txt |
That is, the conversion to ` span ` happens on the way into the function. For
` dynamic_span ` , it’s still a constant expression here - so either we can
still treat it as a constant expression for constraint purposes (as with the
function parameter constraints approach in P1733) or we can add an overloaded
constructo... | |
cpp_utility/constexprarraysize_47_0.txt | void f(std::span<int, 5>); | |
cpp_utility/0eQsx6ip1DwJpli1_37_0.txt | int main ()
{
constexpr int i1 = foo ();
constexpr int i2 = bar ();
//constepxr int i3 = baz(); // don't compile
} | |
cpp_utility/CanIconstexpranstdar_46_0.txt | There’s v | |
cpp_utility/0eQsx6ip1DwJpli1_220_0.txt | >> Hello,
> I'm playing around with the relaxed constraints on constexpr functions with
> clang + libc++ trunk and noticed something strange with std::array : Because
> std::array lacks a constexpr "reference operator[]" (23.3.2.1.3), it is
> impossible to instantiate an std::array in a constepxr function and write in... | |
cpp_utility/constexprarraysize_54_0.txt | In the case I’m describing here, the size is encoded in the type. So if we
change the way we query the size to query based on the type of the object
instead of the value of the object, we can side-step these problems: | |
cpp_utility/0eQsx6ip1DwJpli1_81_0.txt | Copy link | |
cpp_utility/CanIconstexpranstdar_25_0.txt | Of course you cannot make it to be a constexpr. I believe the error message already gave you some hints. Simply, a constexpr variable is not a runtime variable and it is reduced just to its value at compile time. Hence to make compiler work manageable constexpr is required to be of literal type : C++ named requirements... | |
cpp_utility/constexprarraysize_16_0.txt |
Macro notwithstanding, this works fine in all contexts. In C++, it
unfortunately also compiles for any types with overloaded ` operator[] ` and
gives a nonsense result. Can we provide a type-safe way to do better? | |
cpp_utility/CanIconstexpranstdar_23_0.txt | When you instantiate a std::array, you have to provide an element type and the total array size in elements. Both the element type and size become part of the type for the newly-instantiated std::array. These details | |
cpp_utility/76362_84_0.txt | consteval function works fine (constexpr function is not though) | |
cpp_utility/constexprarraysize_21_0.txt |
All compilers reject ` s1 ` (gcc still accepted it when I started writing this
post, but [ that bug ](https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66477) has
been fixed. That’s some timing!) | |
cpp_utility/0eQsx6ip1DwJpli1_262_0.txt | Show original message | |
cpp_utility/0eQsx6ip1DwJpli1_273_0.txt | unread, | |
cpp_utility/cpp_tag_1_1.txt | lity/breakpoint "cpp/utility/breakpoint") (C++26)
[ Three-way comparison ](/w/cpp/utility#Three-way_comparison "cpp/utility")
[ three_way_comparable three_way_comparable_with
](/w/cpp/utility/compare/three_way_comparable "cpp/utility/compare/three way
comparable") (C++20) (C++20)
[ strong_ordering ](/w/cpp/uti... | |
cpp_utility/0eQsx6ip1DwJpli1_290_0.txt | I just want to say again that with the current draft we can use and modify
plain C-array in constexpr function but not std::array, it should be a defect,
no ? | |
cpp_utility/CanIconstexpranstdar_9_0.txt | constexpr int f(int const *p) { return *p; }
int main() {
constexpr int x = 42;
constexpr int y = f(&x); // Okay.
constexpr int const *p = &x; // Error.
int const *q = &x; // Okay.
}
Note how the address of the local variable x can be used to compute a consta | |
cpp_utility/constexprarraysize_108_0.txt | ](/c++/2020/03/30/span-comparisons/) | |
cpp_utility/constexprarraysize_98_0.txt | Basically, the best way to get the size of an array to be used as a constant
expression is still to use a macro - in C++, we can make that macro more type
safe than the initial C version, but still a macro. | |
cpp_utility/0eQsx6ip1DwJpli1_186_0.txt | Sign in to reply to author | |
cpp_utility/0eQsx6ip1DwJpli1_271_0.txt |  | |
cpp_utility/0eQsx6ip1DwJpli1_250_0.txt | ### thomas....@gmail.com | |
cpp_utility/constexprarraysize_64_0.txt |
` s ` ’s size is a constant expression, but it’s not tied to its type - these
type- based approaches wouldn’t work. | |
cpp_utility/0eQsx6ip1DwJpli1_194_0.txt | Show original message | |
cpp_utility/0eQsx6ip1DwJpli1_7_0.txt | [ Sign in
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cpp_utility/76362_33_0.txt | Name | |
cpp_utility/0eQsx6ip1DwJpli1_184_0.txt | Oct 14, 2013, 3:06:27 PM 10/14/13 | |
cpp_utility/constexprarraysize_34_0.txt | Before getting into more detail about the problem itself, let’s take a look at
why this matters. The following is just one motivating example. I picked it
because it’s probably the easiest to look at, but just keep in mind that this
is far from the only reason we might care about this sort of thing. | |
cpp_utility/CanIconstexpranstdar_22_0.txt | For example, I can pass around an arbitrary data structure in C++ by simply taking its address and casting to void *. I can pass the resulting pointer quite efficiently to a function that accepts a void *; however, that function is quite limited in what it can do with that pointer. | |
cpp_utility/CanIconstexpranstdar_10_0.txt | Related questions
Why can't std::map be constexpr?
How do I use the C++20 constexpr std::vector?
Is std::vector faster than std::array?
Why is there std::array<> in C++11? What are the benefits of it?
When should one use std::array instead std::vector? What does std::array offer that std::vector lacks?
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