A way to specify the value category of the *this pointer in a member function.
Questions tagged [ref-qualifier]
47 questions
5
votes
1 answer
LValue ref qualified member function being called on an RValue object
I'm trying to figure out why the following snippet calls the LValue cast operator overload:
#include
class Foo
{
public:
Foo(int i = 0) : i(i) {}
operator const int& () const &
{
std::cout << "lvalue\n";
…
Christopher Leong
- 400
- 2
- 17
5
votes
0 answers
Perfect forwarding and ref-qualifiers for member functions
C++11 introduced the ability to ref-qualify member functions, as well as perfect forwarding. But can we mix them together?
Consider this (working) example:
struct bar{
std::string str;
void do_stuff() & {
/* version 1 */
}
…
Bernard
- 5,209
- 1
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- 64
4
votes
0 answers
What is the rationale behind std::make_[un]signed to copy cv but not ref qualifiers
While trying to implement a make_signed_with_fallback for non integral types i noticed that std::make_[un]signed is designed to copy cv but not ref qualifiers and I'm wondering why.
The only explanation I can think of is that copying ref qualifiers…
jesses
- 559
- 3
- 15
4
votes
1 answer
Returning by value or by rvalue reference from rvalue reference qualified member function?
In Effective Modern C++, Item 12, Scott Meyers writes the following class to show how useful overloading member functions on the reference qualifiers can be:
class Widget {
public:
using DataType = std::vector;
…
DataType& data()…
Enlico
- 23,259
- 6
- 48
- 102
4
votes
1 answer
ref-qualifiers for the assignment operator of standard library types
I was wondering, is there a reason the assignment operator of standard types is not lvalue ref-qualified? None of them are.
Because of that, we can write things such as this:
std::string{} = "42";
std::string s = "hello " + std::string{"world"} =…
Marius Bancila
- 16,053
- 9
- 49
- 91
4
votes
2 answers
Trailing return type, declval and reference qualifiers: can they work together?
Consider the following example:
#include
struct A { void f() {} };
struct B { void f() & {} };
struct C { void f() && {} };
template
auto f() -> decltype(std::declval().f())
{}
int main() {
f();
// f(); //…
skypjack
- 49,335
- 19
- 95
- 187
4
votes
1 answer
Reference qualifiers and deleted member methods
Consider the following code:
#include
struct S {
void f(int) = delete;
void f(int) && { }
};
int main() { }
It doesn't compile saying that the member method cannot be overloaded and it makes sense, of course.
On the other side,…
skypjack
- 49,335
- 19
- 95
- 187
3
votes
1 answer
When are ref-qualified member functions necessary
As I understand it, ref-qualified member-functions are used to distinguish between operating on an implicit this as an lvalue versus an rvalue. If we define a member function without the ref-qualification, then both lvalues and rvalues call the same…
John James
- 219
- 1
- 8
3
votes
1 answer
Generating the necessary ref-qualified overloads for a member function
I have this class:
template
class Array {
private:
T array[N];
public:
template
constexpr Array(InitValues... init_values)
: array{ init_values... } {}
…
Alex Vergara
- 1,766
- 1
- 10
- 29
3
votes
0 answers
C++ user-defined conversions, ref-qualifiers and overload resolution
Please, help me understand what's wrong with this piece of code:
#include
#include
class Sample
{
public:
explicit Sample(std::string data):
_data(std::move(data))
{}
operator const std::string &() const & {…
Yurii A
- 369
- 2
- 10
3
votes
2 answers
implicit object parameter and this pointer
With reference to Non-static member functions, under
const-, volatile-, and ref-qualified member functions
it is mentioned:
A non-static member function can be declared with no ref-qualifier,
with an lvalue ref-qualifier (the token & after the…
Vinod
- 925
- 8
- 9
3
votes
0 answers
WG21 rationale for not using ref-qualifiers
Which WG21 documents explain the decision not to include ref-qualifiers in most standard library classes?
An example that would benefit from such inclusion:
template
C1 container_cast(C2&& source)
{
C1 dest;
// if…
Roman Odaisky
- 2,811
- 22
- 26
3
votes
1 answer
Why is void B::f() const & chosen when B::f is called by a temporary object of B?
#include
struct A
{
void f() const &
{
std::cout << "A::f()&" << std::endl;
}
void f() const &&
{
std::cout << "A::f()&&" << std::endl;
}
};
struct B
{
void f() const &
{
…
xmllmx
- 39,765
- 26
- 162
- 323
3
votes
1 answer
Is it a good practice to return the r-value reference from the r-value ref-qualified method?
As I can see the general rule is not to return r-value references from functions at all (except for rare special cases). But what about class methods?
There is an example in the C++ standard library of returning r-value reference from the r-value…
Constructor
- 7,273
- 2
- 24
- 66
3
votes
1 answer
How do I remove code duplication between similar ref-qualified member functions?
Similarly to How do I remove code duplication between similar const and non-const member functions?, I want to remove the code duplication between nearly identical member functions, except for ref qualifiers.
Let's say I have a class that's…
Justin
- 24,288
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- 142