Structured binding on constWhat is the difference between const int*, const int * const, and int const *?String literal in templates - different behavior of compilersstructured binding with [[maybe_unused]]Capturing array of vectors in lambda makes elements constExplicit destructor call with decltypeWhy “int & const” compiles fine with MSVC?Discards qualifiers unknown cause (std::bind() / lambda)Visual accept std::string from std::byte iteratorC++17 - Binding rvalue reference to non-const lvalue refShall structured binding to a copy of a const c-array be const?
Bob has never been a M before
In Star Trek IV, why did the Bounty go back to a time when whales are already rare?
THT: What is a squared annular “ring”?
Can I rely on this github repository files?
Does the Mind Blank spell prevent the target from being frightened?
How do I implement a file system driver driver in Linux?
Can I use my Chinese passport to enter China after I acquired another citizenship?
How do you respond to a colleague from another team when they're wrongly expecting that you'll help them?
How to color a curve
How will losing mobility of one hand affect my career as a programmer?
Reply 'no position' while the job posting is still there
Query about absorption line spectra
Can a significant change in incentives void an employment contract?
What is the grammatical term for “‑ed” words like these?
Have I saved too much for retirement so far?
Journal losing indexing services
Is it possible to have a strip of cold climate in the middle of a planet?
Can I Retrieve Email Addresses from BCC?
Engineer refusing to file/disclose patents
We have a love-hate relationship
When quoting, must I also copy hyphens used to divide words that continue on the next line?
What (else) happened July 1st 1858 in London?
If a character with the Alert feat rolls a crit fail on their Perception check, are they surprised?
Difference between -| and |- in TikZ
Structured binding on const
What is the difference between const int*, const int * const, and int const *?String literal in templates - different behavior of compilersstructured binding with [[maybe_unused]]Capturing array of vectors in lambda makes elements constExplicit destructor call with decltypeWhy “int & const” compiles fine with MSVC?Discards qualifiers unknown cause (std::bind() / lambda)Visual accept std::string from std::byte iteratorC++17 - Binding rvalue reference to non-const lvalue refShall structured binding to a copy of a const c-array be const?
Is the following code supposed to compile?
void foo()
const std::pair<int, int> x = 1, 2;
auto [a, b] = x;
static_assert(std::is_const_v<decltype(a)>);
static_assert(std::is_const_v<decltype(b)>);
MSVC says "yes!".
GCC says "oh no, man!".
Clang says "no way!".
So, is this an MSVC bug?
The standard is not straightforward here (I had a quick look), but considering the rules for auto, I suppose, a and b should be copied discarding cv-qualifier.
c++ c++17 structured-bindings
asked 6 hours ago
Biagio FestaBiagio Festa
5,18821239
add a comment |
Is the following code supposed to compile?
void foo()
const std::pair<int, int> x = 1, 2;
auto [a, b] = x;
static_assert(std::is_const_v<decltype(a)>);
static_assert(std::is_const_v<decltype(b)>);
MSVC says "yes!".
GCC says "oh no, man!".
Clang says "no way!".
So, is this an MSVC bug?
The standard is not straightforward here (I had a quick look), but considering the rules for auto, I suppose, a and b should be copied discarding cv-qualifier.
c++ c++17 structured-bindings
asked 6 hours ago
Biagio FestaBiagio Festa
5,18821239
add a comment |
Is the following code supposed to compile?
void foo()
const std::pair<int, int> x = 1, 2;
auto [a, b] = x;
static_assert(std::is_const_v<decltype(a)>);
static_assert(std::is_const_v<decltype(b)>);
MSVC says "yes!".
GCC says "oh no, man!".
Clang says "no way!".
So, is this an MSVC bug?
The standard is not straightforward here (I had a quick look), but considering the rules for auto, I suppose, a and b should be copied discarding cv-qualifier.
c++ c++17 structured-bindings
asked 6 hours ago
Biagio FestaBiagio Festa
5,18821239
Is the following code supposed to compile?
void foo()
const std::pair<int, int> x = 1, 2;
auto [a, b] = x;
static_assert(std::is_const_v<decltype(a)>);
static_assert(std::is_const_v<decltype(b)>);
MSVC says "yes!".
GCC says "oh no, man!".
Clang says "no way!".
So, is this an MSVC bug?
The standard is not straightforward here (I had a quick look), but considering the rules for auto, I suppose, a and b should be copied discarding cv-qualifier.
c++ c++17 structured-bindings
c++ c++17 structured-bindings
asked 6 hours ago
Biagio FestaBiagio Festa
5,18821239
asked 6 hours ago
Biagio FestaBiagio Festa
5,18821239
asked 6 hours ago
Biagio FestaBiagio Festa
5,18821239
asked 6 hours ago
Biagio FestaBiagio Festa
5,18821239
asked 6 hours ago
Biagio FestaBiagio Festa
5,18821239
5,18821239
add a comment |
add a comment |
2 Answers
2
active
oldest
votes
Is the following code supposed to compile?
It is not. This is an MSVC bug.
A structured binding declaration introduces a new name (for specification only), e, that is declared like:
auto e = x;
The type of e is called E, and since the initializer is tuple-like, the types of the bindings are given by tuple_element_t<i, E>. In this case E is pair<int, int>, so the two types are just int. The rule for decltype of a structured binding is to give the referenced type, so decltype(a) and decltype(b) are both int.
The important part here is that a and b (the structured bindings) come from the invented variable (e), and not its initializer (x). e is not const because you just declared it auto. What we're doing is copying x, and then taking bindings into this (non-const) copy.
answered 6 hours ago
BarryBarry
185k21325600
add a comment |
The static assertions should fail (so this would be an MSVC bug I guess). Why? Because it's basically the same as the case of:
void foo()
const int x_1 = 1;
const int x_2 = 2;
auto a = x_1;
auto b = x_2;
static_assert(std::is_const_v<decltype(a)>);
static_assert(std::is_const_v<decltype(b)>);
which does indeed fail on MSVC as well.
In C++ expression types decay on assignment: the auto sees an int, not a const int. Structured binding simply lets you do more than a single auto binding at a time.
answered 6 hours ago
einpoklumeinpoklum
36.1k28132260
add a comment |
Your Answer
StackExchange.ifUsing("editor", function ()
StackExchange.using("externalEditor", function ()
StackExchange.using("snippets", function ()
StackExchange.snippets.init();
);
);
, "code-snippets");
StackExchange.ready(function()
var channelOptions =
tags: "".split(" "),
id: "1"
;
initTagRenderer("".split(" "), "".split(" "), channelOptions);
StackExchange.using("externalEditor", function()
// Have to fire editor after snippets, if snippets enabled
if (StackExchange.settings.snippets.snippetsEnabled)
StackExchange.using("snippets", function()
createEditor();
);
else
createEditor();
);
function createEditor()
StackExchange.prepareEditor(
heartbeatType: 'answer',
autoActivateHeartbeat: false,
convertImagesToLinks: true,
noModals: true,
showLowRepImageUploadWarning: true,
reputationToPostImages: 10,
bindNavPrevention: true,
postfix: "",
imageUploader:
brandingHtml: "Powered by u003ca class="icon-imgur-white" href="https://imgur.com/"u003eu003c/au003e",
contentPolicyHtml: "User contributions licensed under u003ca href="https://creativecommons.org/licenses/by-sa/3.0/"u003ecc by-sa 3.0 with attribution requiredu003c/au003e u003ca href="https://stackoverflow.com/legal/content-policy"u003e(content policy)u003c/au003e",
allowUrls: true
,
onDemand: true,
discardSelector: ".discard-answer"
,immediatelyShowMarkdownHelp:true
);
);
Sign up or log in
StackExchange.ready(function ()
StackExchange.helpers.onClickDraftSave('#login-link');
);
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
StackExchange.ready(
function ()
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fstackoverflow.com%2fquestions%2f55329651%2fstructured-binding-on-const%23new-answer', 'question_page');
);
Post as a guest
Required, but never shown
2 Answers
2
active
oldest
votes
2 Answers
2
active
oldest
votes
active
oldest
votes
active
oldest
votes
Is the following code supposed to compile?
It is not. This is an MSVC bug.
A structured binding declaration introduces a new name (for specification only), e, that is declared like:
auto e = x;
The type of e is called E, and since the initializer is tuple-like, the types of the bindings are given by tuple_element_t<i, E>. In this case E is pair<int, int>, so the two types are just int. The rule for decltype of a structured binding is to give the referenced type, so decltype(a) and decltype(b) are both int.
The important part here is that a and b (the structured bindings) come from the invented variable (e), and not its initializer (x). e is not const because you just declared it auto. What we're doing is copying x, and then taking bindings into this (non-const) copy.
answered 6 hours ago
BarryBarry
185k21325600
add a comment |
Is the following code supposed to compile?
It is not. This is an MSVC bug.
A structured binding declaration introduces a new name (for specification only), e, that is declared like:
auto e = x;
The type of e is called E, and since the initializer is tuple-like, the types of the bindings are given by tuple_element_t<i, E>. In this case E is pair<int, int>, so the two types are just int. The rule for decltype of a structured binding is to give the referenced type, so decltype(a) and decltype(b) are both int.
The important part here is that a and b (the structured bindings) come from the invented variable (e), and not its initializer (x). e is not const because you just declared it auto. What we're doing is copying x, and then taking bindings into this (non-const) copy.
answered 6 hours ago
BarryBarry
185k21325600
add a comment |
Is the following code supposed to compile?
It is not. This is an MSVC bug.
A structured binding declaration introduces a new name (for specification only), e, that is declared like:
auto e = x;
The type of e is called E, and since the initializer is tuple-like, the types of the bindings are given by tuple_element_t<i, E>. In this case E is pair<int, int>, so the two types are just int. The rule for decltype of a structured binding is to give the referenced type, so decltype(a) and decltype(b) are both int.
The important part here is that a and b (the structured bindings) come from the invented variable (e), and not its initializer (x). e is not const because you just declared it auto. What we're doing is copying x, and then taking bindings into this (non-const) copy.
answered 6 hours ago
BarryBarry
185k21325600
Is the following code supposed to compile?
It is not. This is an MSVC bug.
A structured binding declaration introduces a new name (for specification only), e, that is declared like:
auto e = x;
The type of e is called E, and since the initializer is tuple-like, the types of the bindings are given by tuple_element_t<i, E>. In this case E is pair<int, int>, so the two types are just int. The rule for decltype of a structured binding is to give the referenced type, so decltype(a) and decltype(b) are both int.
The important part here is that a and b (the structured bindings) come from the invented variable (e), and not its initializer (x). e is not const because you just declared it auto. What we're doing is copying x, and then taking bindings into this (non-const) copy.
answered 6 hours ago
BarryBarry
185k21325600
answered 6 hours ago
BarryBarry
185k21325600
answered 6 hours ago
BarryBarry
185k21325600
answered 6 hours ago
BarryBarry
185k21325600
185k21325600
add a comment |
add a comment |
The static assertions should fail (so this would be an MSVC bug I guess). Why? Because it's basically the same as the case of:
void foo()
const int x_1 = 1;
const int x_2 = 2;
auto a = x_1;
auto b = x_2;
static_assert(std::is_const_v<decltype(a)>);
static_assert(std::is_const_v<decltype(b)>);
which does indeed fail on MSVC as well.
In C++ expression types decay on assignment: the auto sees an int, not a const int. Structured binding simply lets you do more than a single auto binding at a time.
answered 6 hours ago
einpoklumeinpoklum
36.1k28132260
add a comment |
The static assertions should fail (so this would be an MSVC bug I guess). Why? Because it's basically the same as the case of:
void foo()
const int x_1 = 1;
const int x_2 = 2;
auto a = x_1;
auto b = x_2;
static_assert(std::is_const_v<decltype(a)>);
static_assert(std::is_const_v<decltype(b)>);
which does indeed fail on MSVC as well.
In C++ expression types decay on assignment: the auto sees an int, not a const int. Structured binding simply lets you do more than a single auto binding at a time.
answered 6 hours ago
einpoklumeinpoklum
36.1k28132260
add a comment |
The static assertions should fail (so this would be an MSVC bug I guess). Why? Because it's basically the same as the case of:
void foo()
const int x_1 = 1;
const int x_2 = 2;
auto a = x_1;
auto b = x_2;
static_assert(std::is_const_v<decltype(a)>);
static_assert(std::is_const_v<decltype(b)>);
which does indeed fail on MSVC as well.
In C++ expression types decay on assignment: the auto sees an int, not a const int. Structured binding simply lets you do more than a single auto binding at a time.
answered 6 hours ago
einpoklumeinpoklum
36.1k28132260
The static assertions should fail (so this would be an MSVC bug I guess). Why? Because it's basically the same as the case of:
void foo()
const int x_1 = 1;
const int x_2 = 2;
auto a = x_1;
auto b = x_2;
static_assert(std::is_const_v<decltype(a)>);
static_assert(std::is_const_v<decltype(b)>);
which does indeed fail on MSVC as well.
In C++ expression types decay on assignment: the auto sees an int, not a const int. Structured binding simply lets you do more than a single auto binding at a time.
answered 6 hours ago
einpoklumeinpoklum
36.1k28132260
edited 6 hours ago
answered 6 hours ago
einpoklumeinpoklum
36.1k28132260
answered 6 hours ago
einpoklumeinpoklum
36.1k28132260
answered 6 hours ago
einpoklumeinpoklum
36.1k28132260
36.1k28132260
add a comment |
add a comment |
Thanks for contributing an answer to Stack Overflow!
- Please be sure to answer the question. Provide details and share your research!
But avoid …
- Asking for help, clarification, or responding to other answers.
- Making statements based on opinion; back them up with references or personal experience.
To learn more, see our tips on writing great answers.
Sign up or log in
StackExchange.ready(function ()
StackExchange.helpers.onClickDraftSave('#login-link');
);
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
StackExchange.ready(
function ()
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fstackoverflow.com%2fquestions%2f55329651%2fstructured-binding-on-const%23new-answer', 'question_page');
);
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function ()
StackExchange.helpers.onClickDraftSave('#login-link');
);
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function ()
StackExchange.helpers.onClickDraftSave('#login-link');
);
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function ()
StackExchange.helpers.onClickDraftSave('#login-link');
);
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
