C++ class constructors qualified as __attribute__((pure)) or __attribute__((const))
Can and should C++ class constructors be declared __attribute__((pure)) if they only can reach data via its parameters? And in which cases should they be qualified as __attribute__((const))?
c++ attributes pure-function
asked Nov 19 '18 at 13:06
NordlöwNordlöw
5,36434184
add a comment |
Can and should C++ class constructors be declared __attribute__((pure)) if they only can reach data via its parameters? And in which cases should they be qualified as __attribute__((const))?
c++ attributes pure-function
asked Nov 19 '18 at 13:06
NordlöwNordlöw
5,36434184
Err, what's the point? When will an average well-formed program going to invoke a c'tor for the same object twice?
– StoryTeller
Nov 19 '18 at 13:09
Ahh, I didn't think of the fact that it creates/allocates a new instance. I guess it's not relevant to qualify constructors then.
– Nordlöw
Nov 19 '18 at 13:11
add a comment |
Can and should C++ class constructors be declared __attribute__((pure)) if they only can reach data via its parameters? And in which cases should they be qualified as __attribute__((const))?
c++ attributes pure-function
asked Nov 19 '18 at 13:06
NordlöwNordlöw
5,36434184
Can and should C++ class constructors be declared __attribute__((pure)) if they only can reach data via its parameters? And in which cases should they be qualified as __attribute__((const))?
c++ attributes pure-function
c++ attributes pure-function
asked Nov 19 '18 at 13:06
NordlöwNordlöw
5,36434184
asked Nov 19 '18 at 13:06
NordlöwNordlöw
5,36434184
asked Nov 19 '18 at 13:06
NordlöwNordlöw
5,36434184
asked Nov 19 '18 at 13:06
NordlöwNordlöw
5,36434184
asked Nov 19 '18 at 13:06
NordlöwNordlöw
5,36434184
5,36434184
Err, what's the point? When will an average well-formed program going to invoke a c'tor for the same object twice?
– StoryTeller
Nov 19 '18 at 13:09
Ahh, I didn't think of the fact that it creates/allocates a new instance. I guess it's not relevant to qualify constructors then.
– Nordlöw
Nov 19 '18 at 13:11
add a comment |
Err, what's the point? When will an average well-formed program going to invoke a c'tor for the same object twice?
– StoryTeller
Nov 19 '18 at 13:09
Ahh, I didn't think of the fact that it creates/allocates a new instance. I guess it's not relevant to qualify constructors then.
– Nordlöw
Nov 19 '18 at 13:11
Err, what's the point? When will an average well-formed program going to invoke a c'tor for the same object twice?
– StoryTeller
Nov 19 '18 at 13:09
Err, what's the point? When will an average well-formed program going to invoke a c'tor for the same object twice?
– StoryTeller
Nov 19 '18 at 13:09
Ahh, I didn't think of the fact that it creates/allocates a new instance. I guess it's not relevant to qualify constructors then.
– Nordlöw
Nov 19 '18 at 13:11
Ahh, I didn't think of the fact that it creates/allocates a new instance. I guess it's not relevant to qualify constructors then.
– Nordlöw
Nov 19 '18 at 13:11
add a comment |
1 Answer
1
active
oldest
votes
GCC warns when you qualify constructors as pure or const. This is because a constructor does not return anything (returns void) and it does not make much sense to have a pure or const attributes on such functions.
See godbolt demo here.
<source>:3:30: warning: 'pure' attribute on function returning 'void' [-Wattributes]
A() __attribute__((pure));
^
<source>:8:31: warning: 'const' attribute on function returning 'void' [-Wattributes]
B() __attribute__((const)); ^
From GCC documentation:
const
...
Because a const function cannot have any side effects it does not make sense for such a function to return void. Declaring such a function is diagnosed.
pure
...
Because a pure function cannot have any side effects it does not make sense for such a function to return void. Declaring such a function is diagnosed.
answered Nov 19 '18 at 13:34
P.WP.W
13.3k31245
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%2f53375307%2fc-class-constructors-qualified-as-attribute-pure-or-attribute-cons%23new-answer', 'question_page');
}
);
Post as a guest
Required, but never shown
1 Answer
1
active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
GCC warns when you qualify constructors as pure or const. This is because a constructor does not return anything (returns void) and it does not make much sense to have a pure or const attributes on such functions.
See godbolt demo here.
<source>:3:30: warning: 'pure' attribute on function returning 'void' [-Wattributes]
A() __attribute__((pure));
^
<source>:8:31: warning: 'const' attribute on function returning 'void' [-Wattributes]
B() __attribute__((const)); ^
From GCC documentation:
const
...
Because a const function cannot have any side effects it does not make sense for such a function to return void. Declaring such a function is diagnosed.
pure
...
Because a pure function cannot have any side effects it does not make sense for such a function to return void. Declaring such a function is diagnosed.
answered Nov 19 '18 at 13:34
P.WP.W
13.3k31245
add a comment |
GCC warns when you qualify constructors as pure or const. This is because a constructor does not return anything (returns void) and it does not make much sense to have a pure or const attributes on such functions.
See godbolt demo here.
<source>:3:30: warning: 'pure' attribute on function returning 'void' [-Wattributes]
A() __attribute__((pure));
^
<source>:8:31: warning: 'const' attribute on function returning 'void' [-Wattributes]
B() __attribute__((const)); ^
From GCC documentation:
const
...
Because a const function cannot have any side effects it does not make sense for such a function to return void. Declaring such a function is diagnosed.
pure
...
Because a pure function cannot have any side effects it does not make sense for such a function to return void. Declaring such a function is diagnosed.
answered Nov 19 '18 at 13:34
P.WP.W
13.3k31245
add a comment |
GCC warns when you qualify constructors as pure or const. This is because a constructor does not return anything (returns void) and it does not make much sense to have a pure or const attributes on such functions.
See godbolt demo here.
<source>:3:30: warning: 'pure' attribute on function returning 'void' [-Wattributes]
A() __attribute__((pure));
^
<source>:8:31: warning: 'const' attribute on function returning 'void' [-Wattributes]
B() __attribute__((const)); ^
From GCC documentation:
const
...
Because a const function cannot have any side effects it does not make sense for such a function to return void. Declaring such a function is diagnosed.
pure
...
Because a pure function cannot have any side effects it does not make sense for such a function to return void. Declaring such a function is diagnosed.
answered Nov 19 '18 at 13:34
P.WP.W
13.3k31245
GCC warns when you qualify constructors as pure or const. This is because a constructor does not return anything (returns void) and it does not make much sense to have a pure or const attributes on such functions.
See godbolt demo here.
<source>:3:30: warning: 'pure' attribute on function returning 'void' [-Wattributes]
A() __attribute__((pure));
^
<source>:8:31: warning: 'const' attribute on function returning 'void' [-Wattributes]
B() __attribute__((const)); ^
From GCC documentation:
const
...
Because a const function cannot have any side effects it does not make sense for such a function to return void. Declaring such a function is diagnosed.
pure
...
Because a pure function cannot have any side effects it does not make sense for such a function to return void. Declaring such a function is diagnosed.
answered Nov 19 '18 at 13:34
P.WP.W
13.3k31245
answered Nov 19 '18 at 13:34
P.WP.W
13.3k31245
answered Nov 19 '18 at 13:34
P.WP.W
13.3k31245
answered Nov 19 '18 at 13:34
P.WP.W
13.3k31245
13.3k31245
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%2f53375307%2fc-class-constructors-qualified-as-attribute-pure-or-attribute-cons%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
Err, what's the point? When will an average well-formed program going to invoke a c'tor for the same object twice?
– StoryTeller
Nov 19 '18 at 13:09
Ahh, I didn't think of the fact that it creates/allocates a new instance. I guess it's not relevant to qualify constructors then.
– Nordlöw
Nov 19 '18 at 13:11