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?
Folder comparison
Can somebody explain Brexit in a few child-proof sentences?
Some numbers are more equivalent than others
Structured binding on const
What (else) happened July 1st 1858 in London?
Greatest common substring
Java - What do constructor type arguments mean when placed *before* the type?
Can I sign legal documents with a smiley face?
How do you respond to a colleague from another team when they're wrongly expecting that you'll help them?
Does the Mind Blank spell prevent the target from being frightened?
Are all species of CANNA edible?
How can "mimic phobia" be cured or prevented?
Engineer refusing to file/disclose patents
Greco-Roman egalitarianism
What does this horizontal bar at the first measure mean?
Will adding a BY-SA image to a blog post make the entire post BY-SA?
Could the E-bike drivetrain wear down till needing replacement after 400 km?
Visiting the UK as unmarried couple
How do ground effect vehicles perform turns?
Freedom of speech and where it applies
Should I install hardwood flooring or cabinets first?
Drawing ramified coverings with tikz
Can someone explain how this makes sense electrically?
What linear sensor for a keyboard?
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
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
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
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
5,19321239
5,19321239
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.
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.
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.
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.
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.
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
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.
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.
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.
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.
edited 6 hours ago
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