Mixing
How can I accept both rvalue and lvalue non-const parameter type
I'm repeatedly running into the problem of accepting a non-const reference parameter, since it seems taking an rvalue parameter prevents accepting lvalues and vice versa. Here's an example
void read(File &file)// I want to modify file
{
SomeClass someObject;
file.readInto(&someObject);//readInto is a non-const method
// do something with the data populated in someObject
}
But when I try to call read I have a problem if I try two different calling conventions
//this works just fine
File f1 = File::open("some_file_path");
read(f1);
// However this fails
read( File::open("some_file_path") );//because open returns an rvalue
The problem I have is if I change the parameter to a non-const rvalue than I can't pass the lvalue anymore. Am I doomed to always provide an override (or template) that takes the rvalue reference type and simply calls out to the lvalue override?
c++11 rvalue-reference pass-by-rvalue-reference
asked Nov 21 '18 at 22:48
xaviersjsxaviersjs
5211716
add a comment |
I'm repeatedly running into the problem of accepting a non-const reference parameter, since it seems taking an rvalue parameter prevents accepting lvalues and vice versa. Here's an example
void read(File &file)// I want to modify file
{
SomeClass someObject;
file.readInto(&someObject);//readInto is a non-const method
// do something with the data populated in someObject
}
But when I try to call read I have a problem if I try two different calling conventions
//this works just fine
File f1 = File::open("some_file_path");
read(f1);
// However this fails
read( File::open("some_file_path") );//because open returns an rvalue
The problem I have is if I change the parameter to a non-const rvalue than I can't pass the lvalue anymore. Am I doomed to always provide an override (or template) that takes the rvalue reference type and simply calls out to the lvalue override?
c++11 rvalue-reference pass-by-rvalue-reference
asked Nov 21 '18 at 22:48
xaviersjsxaviersjs
5211716
Possible duplicate of How come a non-const reference cannot bind to a temporary object?
– md5i
Nov 22 '18 at 5:01
add a comment |
I'm repeatedly running into the problem of accepting a non-const reference parameter, since it seems taking an rvalue parameter prevents accepting lvalues and vice versa. Here's an example
void read(File &file)// I want to modify file
{
SomeClass someObject;
file.readInto(&someObject);//readInto is a non-const method
// do something with the data populated in someObject
}
But when I try to call read I have a problem if I try two different calling conventions
//this works just fine
File f1 = File::open("some_file_path");
read(f1);
// However this fails
read( File::open("some_file_path") );//because open returns an rvalue
The problem I have is if I change the parameter to a non-const rvalue than I can't pass the lvalue anymore. Am I doomed to always provide an override (or template) that takes the rvalue reference type and simply calls out to the lvalue override?
c++11 rvalue-reference pass-by-rvalue-reference
asked Nov 21 '18 at 22:48
xaviersjsxaviersjs
5211716
I'm repeatedly running into the problem of accepting a non-const reference parameter, since it seems taking an rvalue parameter prevents accepting lvalues and vice versa. Here's an example
void read(File &file)// I want to modify file
{
SomeClass someObject;
file.readInto(&someObject);//readInto is a non-const method
// do something with the data populated in someObject
}
But when I try to call read I have a problem if I try two different calling conventions
//this works just fine
File f1 = File::open("some_file_path");
read(f1);
// However this fails
read( File::open("some_file_path") );//because open returns an rvalue
The problem I have is if I change the parameter to a non-const rvalue than I can't pass the lvalue anymore. Am I doomed to always provide an override (or template) that takes the rvalue reference type and simply calls out to the lvalue override?
c++11 rvalue-reference pass-by-rvalue-reference
c++11 rvalue-reference pass-by-rvalue-reference
asked Nov 21 '18 at 22:48
xaviersjsxaviersjs
5211716
asked Nov 21 '18 at 22:48
xaviersjsxaviersjs
5211716
edited Nov 21 '18 at 23:07
xaviersjs
asked Nov 21 '18 at 22:48
xaviersjsxaviersjs
5211716
asked Nov 21 '18 at 22:48
xaviersjsxaviersjs
5211716
asked Nov 21 '18 at 22:48
xaviersjsxaviersjs
5211716
5211716
Possible duplicate of How come a non-const reference cannot bind to a temporary object?
– md5i
Nov 22 '18 at 5:01
add a comment |
Possible duplicate of How come a non-const reference cannot bind to a temporary object?
– md5i
Nov 22 '18 at 5:01
Possible duplicate of How come a non-const reference cannot bind to a temporary object?
– md5i
Nov 22 '18 at 5:01
Possible duplicate of How come a non-const reference cannot bind to a temporary object?
– md5i
Nov 22 '18 at 5:01
add a comment |
1 Answer
1
active
oldest
votes
Since you updated the question, I suggest doing this:
void read(File& file)
{
SomeClass someObject;
file.radInto(&someObject);
// ...
}
void read(File&& file) { read(file); }
That will handle both lvalues and rvalues with minimal code repetition.
I think your read function should simply take a File&:
void read(File& file) // I want to modify file
{
SomeClass someObject;
file.readInto(&someObject);//Modifies file
// do something with the data populated in someObject
}
Then you can call:
// OK
std::shared_ptr<File> f1 = File::open("some_file_path");
read(*f1);
// OK
read( *File::open("some_file_path") );
Added benefit: the function is not limited to shared_ptr, and works with any File independently of how its memory is managed.
Alternatively, use a forwarding reference:
template <typename T>
void read(T&& file)// I want to modify file
{
SomeClass someObject;
file->readInto(&someObject);//Modifies file
// do something with the data populated in someObject
}
answered Nov 21 '18 at 22:51
Vittorio RomeoVittorio Romeo
58.3k17158300
You're right. I updated the question to delete the shared_ptr part, but the question remains the same.
– xaviersjs
Nov 21 '18 at 23:09
@xaviersjs: I updated my answer.
– Vittorio Romeo
Nov 22 '18 at 10:37
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%2f53421505%2fhow-can-i-accept-both-rvalue-and-lvalue-non-const-parameter-type%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
Since you updated the question, I suggest doing this:
void read(File& file)
{
SomeClass someObject;
file.radInto(&someObject);
// ...
}
void read(File&& file) { read(file); }
That will handle both lvalues and rvalues with minimal code repetition.
I think your read function should simply take a File&:
void read(File& file) // I want to modify file
{
SomeClass someObject;
file.readInto(&someObject);//Modifies file
// do something with the data populated in someObject
}
Then you can call:
// OK
std::shared_ptr<File> f1 = File::open("some_file_path");
read(*f1);
// OK
read( *File::open("some_file_path") );
Added benefit: the function is not limited to shared_ptr, and works with any File independently of how its memory is managed.
Alternatively, use a forwarding reference:
template <typename T>
void read(T&& file)// I want to modify file
{
SomeClass someObject;
file->readInto(&someObject);//Modifies file
// do something with the data populated in someObject
}
answered Nov 21 '18 at 22:51
Vittorio RomeoVittorio Romeo
58.3k17158300
You're right. I updated the question to delete the shared_ptr part, but the question remains the same.
– xaviersjs
Nov 21 '18 at 23:09
@xaviersjs: I updated my answer.
– Vittorio Romeo
Nov 22 '18 at 10:37
add a comment |
Since you updated the question, I suggest doing this:
void read(File& file)
{
SomeClass someObject;
file.radInto(&someObject);
// ...
}
void read(File&& file) { read(file); }
That will handle both lvalues and rvalues with minimal code repetition.
I think your read function should simply take a File&:
void read(File& file) // I want to modify file
{
SomeClass someObject;
file.readInto(&someObject);//Modifies file
// do something with the data populated in someObject
}
Then you can call:
// OK
std::shared_ptr<File> f1 = File::open("some_file_path");
read(*f1);
// OK
read( *File::open("some_file_path") );
Added benefit: the function is not limited to shared_ptr, and works with any File independently of how its memory is managed.
Alternatively, use a forwarding reference:
template <typename T>
void read(T&& file)// I want to modify file
{
SomeClass someObject;
file->readInto(&someObject);//Modifies file
// do something with the data populated in someObject
}
answered Nov 21 '18 at 22:51
Vittorio RomeoVittorio Romeo
58.3k17158300
You're right. I updated the question to delete the shared_ptr part, but the question remains the same.
– xaviersjs
Nov 21 '18 at 23:09
@xaviersjs: I updated my answer.
– Vittorio Romeo
Nov 22 '18 at 10:37
add a comment |
Since you updated the question, I suggest doing this:
void read(File& file)
{
SomeClass someObject;
file.radInto(&someObject);
// ...
}
void read(File&& file) { read(file); }
That will handle both lvalues and rvalues with minimal code repetition.
I think your read function should simply take a File&:
void read(File& file) // I want to modify file
{
SomeClass someObject;
file.readInto(&someObject);//Modifies file
// do something with the data populated in someObject
}
Then you can call:
// OK
std::shared_ptr<File> f1 = File::open("some_file_path");
read(*f1);
// OK
read( *File::open("some_file_path") );
Added benefit: the function is not limited to shared_ptr, and works with any File independently of how its memory is managed.
Alternatively, use a forwarding reference:
template <typename T>
void read(T&& file)// I want to modify file
{
SomeClass someObject;
file->readInto(&someObject);//Modifies file
// do something with the data populated in someObject
}
answered Nov 21 '18 at 22:51
Vittorio RomeoVittorio Romeo
58.3k17158300
Since you updated the question, I suggest doing this:
void read(File& file)
{
SomeClass someObject;
file.radInto(&someObject);
// ...
}
void read(File&& file) { read(file); }
That will handle both lvalues and rvalues with minimal code repetition.
I think your read function should simply take a File&:
void read(File& file) // I want to modify file
{
SomeClass someObject;
file.readInto(&someObject);//Modifies file
// do something with the data populated in someObject
}
Then you can call:
// OK
std::shared_ptr<File> f1 = File::open("some_file_path");
read(*f1);
// OK
read( *File::open("some_file_path") );
Added benefit: the function is not limited to shared_ptr, and works with any File independently of how its memory is managed.
Alternatively, use a forwarding reference:
template <typename T>
void read(T&& file)// I want to modify file
{
SomeClass someObject;
file->readInto(&someObject);//Modifies file
// do something with the data populated in someObject
}
answered Nov 21 '18 at 22:51
Vittorio RomeoVittorio Romeo
58.3k17158300
edited Nov 22 '18 at 10:37
answered Nov 21 '18 at 22:51
Vittorio RomeoVittorio Romeo
58.3k17158300
answered Nov 21 '18 at 22:51
Vittorio RomeoVittorio Romeo
58.3k17158300
answered Nov 21 '18 at 22:51
Vittorio RomeoVittorio Romeo
58.3k17158300
58.3k17158300
You're right. I updated the question to delete the shared_ptr part, but the question remains the same.
– xaviersjs
Nov 21 '18 at 23:09
@xaviersjs: I updated my answer.
– Vittorio Romeo
Nov 22 '18 at 10:37
add a comment |
You're right. I updated the question to delete the shared_ptr part, but the question remains the same.
– xaviersjs
Nov 21 '18 at 23:09
@xaviersjs: I updated my answer.
– Vittorio Romeo
Nov 22 '18 at 10:37
You're right. I updated the question to delete the shared_ptr part, but the question remains the same.
– xaviersjs
Nov 21 '18 at 23:09
You're right. I updated the question to delete the shared_ptr part, but the question remains the same.
– xaviersjs
Nov 21 '18 at 23:09
@xaviersjs: I updated my answer.
– Vittorio Romeo
Nov 22 '18 at 10:37
@xaviersjs: I updated my answer.
– Vittorio Romeo
Nov 22 '18 at 10:37
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%2f53421505%2fhow-can-i-accept-both-rvalue-and-lvalue-non-const-parameter-type%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
Possible duplicate of How come a non-const reference cannot bind to a temporary object?
– md5i
Nov 22 '18 at 5:01