A way to specify the value category of the *this pointer in a member function.
Questions tagged [ref-qualifier]
47 questions
29
votes
2 answers
What does the & (ampersand) at the end of member function signature mean?
I can't remember which talk it was, but recently I watched some talks from CppCon 2017 and there someone mentioned as some kind of side-note, that the only true way of overloading operator= would be in the following fashion:
class test {
public:
…
Martin B.
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27
votes
1 answer
Overload resolution with ref-qualifiers
While working with ref-qualified function overloads, I'm getting different results from GCC (4.8.1) and Clang (2.9 and trunk). Consider the following code:
#include
#include
struct foo
{
int& bar() &
{
std::cout…
K-ballo
- 80,396
- 20
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19
votes
2 answers
Is there any real use case for function's reference qualifiers?
Recently I learned about function's reference qualifiers, e.g.
struct foo
{
void bar() {}
void bar1() & {}
void bar2() && {}
};
Where I might need this feature, is there any real use case for this language feature ?
tommyk
- 3,187
- 7
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- 61
16
votes
2 answers
Why template argument cannot be deduced in this context?
Could anyone explain why compilers (g++, visual c++) fail to deduce the template argument in this case?
struct MyClass
{
void Foo(int x)& {}
void Foo(int x)&& {}
};
template
void CallFoo(void(T::*func)(int)&)
{
//create…
John
- 161
- 2
14
votes
3 answers
To move, or not to move from r-value ref-qualified method?
In the following C++11+ code which return statement construction should be preferred?
#include
struct Bar
{
};
struct Foo
{
Bar bar;
Bar get() &&
{
return std::move(bar); // 1
return bar; // 2
…
Constructor
- 7,273
- 2
- 24
- 66
11
votes
1 answer
Forwarding cv-ref-qualifier for member functions
If there are no another overloadings (say, f(T &) or f(volatile T &&)) of a (member) function template template< typename T > f(T &&);, then T && is so-called forwarding reference, and T is either U, or U & for some cv-qualified type U. But for…
Tomilov Anatoliy
- 15,657
- 10
- 64
- 169
9
votes
1 answer
ref-qualified member functions as template arguments?
This compiles fine in clang 3.3:
template
struct M;
template
struct M { };
template
struct M { };
but fails in gcc…
iavr
- 7,547
- 1
- 18
- 53
8
votes
1 answer
Why can't a destructor have reference qualifiers?
Is there a reason (other than because the standard says so) to why the following code is not allowed?
struct Foo
{
~Foo() && {}
~Foo() & {}
};
I know that it is illegal, but I wanna know why.
I was thinking about the good old avoid unnamed…
Timo
- 9,269
- 2
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- 58
8
votes
1 answer
Explicit ref-qualified conversion operator templates in action
Given the following conversion operators
struct A
{
template explicit operator T&& () &&;
template explicit operator T& () &;
template explicit operator const T& () const&;
};
struct B…
iavr
- 7,547
- 1
- 18
- 53
7
votes
1 answer
Overloading a parent member function without ref-qualifier with a child member function with ref-qualifier in C++
In C++ one cannot overload in one class a member function with ref-qualifier with a member function without ref-qualifier. But at the same time it is possible to inherit one member function from a parent class and overload it in a child class as in…
Fedor
- 17,146
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7
votes
1 answer
Best practice for getters with ref-qualifier
The following code causes undefined behaviour:
class T
{
public:
const std::string& get() const { return s_; }
private:
std::string s_ { "test" };
}
void breaking()
{
const auto& str = T{}.get();
// do sth with "str" <--…
Tim
- 143
- 1
- 5
7
votes
1 answer
call of overloaded with ref-qualifiers member function is ambiguous
I found a strange behaviour, when compliling my code with G++ (gcc 4.8.1 and MinGW 4.8.2 with -std=gnu++1y flag). In spirit of SSCCE I isolating the following snippet:
struct C
{
template< typename X >
auto
f(X &&) const &
{ ; }
…
Tomilov Anatoliy
- 15,657
- 10
- 64
- 169
6
votes
1 answer
rvalue ref-qualifiers for STL containers
Why element access member functions of STL containers, e.g. std::array::operator[] or std::vector::operator[] do not have rvalue ref-qualifier overloads? Of course I can do std::move(generate_vector()[10]), but I'm curious if adding rvalue…
Junekey Jeon
- 1,496
- 1
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- 18
6
votes
1 answer
Is it reasonable to overload operators by ref-qualifier to prevent temporaries?
It just occurred to me that operator+ & co can operate on this for rvalues; i.e. given a class C, it's possible to do this:
class C {
// ...
C operator-( const C& rhs ) const & {
C result = *this;
result -= rhs;
…
Mr. Wonko
- 690
- 9
- 17
5
votes
2 answers
Why is std::string's member operator= not lvalue ref-qualified
I recently learned that member functions can be ref-qualified, which allows me to write
struct S {
S& operator=(S const&) & // can only be used if the implicit object is an lvalue
{
return *this;
}
};
S operator+(S const &, S…
cigien
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