Questions tagged [reference-wrapper]
107 questions
6
votes
1 answer
How to detect std::reference_wrapper in C++ at compile time
Lets say we have some variadic template and need to treat std::reference_wrapper parameters differently.
How can we achieve that?
Sergei Krivonos
- 4,217
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6
votes
1 answer
Why reference_wrapper behaves differently for built-in types?
I have the following use of std::reference_wrapper for a build in type (double) and for a user defined type (std::string).
Why do they behave differently in the case of the stream operator?
#include //reference…
alfC
- 14,261
- 4
- 67
- 118
6
votes
2 answers
Comparing addresses of reference_wrappers
How can I compare two std::reference_wrappers by the references they hold? I want to see if the references of two std::reference_wrappers are equal or not.
Edit: Sorry from confusion. I meant how to get the addresses of referents and compare them.
Shibli
- 5,879
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5
votes
1 answer
Best way to treat std::reference_wrapper as std::reference_wrapper
I have two classes, say 'Base' and 'Derived', where Derived class inherits Base class.
Then a container of references to Derived class instances (std::vector< std::reference_wrapper< Derived > > myContainer ).
And finally, I have a function that…
sajas
- 1,599
- 1
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- 39
5
votes
3 answers
Reserve a vector of reference_wrapper objects, how it is possible?
std::reference_wrapper isn't default constructable. So I can't write any of:
std::vector> vec(10);
std::array, 3> arr;
However, and to my surprise, you can invoke the std::vector::reserve…
101010
- 41,839
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5
votes
1 answer
When is std::reference_wrapper converted to T&?
Consider the following code:
#include
#include
using namespace std;
template
void fun(T t)
{
t+=8;
}
int main()
{
int i = 0;
fun(ref(i));
cout << i << endl;
}
This code prints "8". I assume…
oz1cz
- 5,504
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4
votes
1 answer
Subscript operator for reference_wrapper
I recently learnt that std::reference_wrapper has an overload for the the function call operator in case T is function-like. I wonder whether there is a reason given by the standard committee to not include an array subscript operator in cases…
Albjenow
- 369
- 2
- 12
4
votes
2 answers
Initialize an array of reference_wrapper
Coming from C to C++, I'm trying to understand the world of smart pointers & references. I've got the following:
class Game {
public:
...
private:
...
static GamePiece EmptyPiece;
reference_wrapper _board[N][M] = {…
galah92
- 3,621
- 2
- 29
- 55
4
votes
1 answer
unordered_map value assignation when value type is reference_wrapper
I am experimenting with std::reference_wrapper. I don't understand why the following does work with a std::vector but not for a std::unordered_map:
#include
#include
#include
using namespace std;
int main()
{
…
valentin
- 2,596
- 6
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4
votes
0 answers
Default constructor with std::reference_wrapper as member?
I have this struct:
struct MyStruct
{
MyStruct(const Wrapper &wrapper, /*...*/) :
wrapper(std::cref(wrapper)), /*...*/ {}
std::reference_wrapper wrapper;
/*...*/
};
However, now I want to use a…
justHelloWorld
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4
votes
1 answer
Overloading operator== for const std::reference_wrapper in std::unordered_map
I can't figure out how to get a std::string reference into an std::unordered_map using a std::reference_wrapper. Per the following link I understand I need to overload operator==.
Why can template instances not be deduced in…
dontarius
- 99
- 1
- 8
3
votes
0 answers
Why does reference_wrapper implement operator() in particular?
std::reference_wrapper is a standard library that wraps a reference in a copyable, assignable object.
My view is that it has a weird design and seems like a hack to trick classes that store objects by value to believe that they are copying a value…
alfC
- 14,261
- 4
- 67
- 118
3
votes
3 answers
Why does reference_wrapper comparison not work?
int main()
{
int x = 1;
auto ref = std::ref(x);
if (x < ref)
{
...
}
}
In the above code, I made an int variable and a reference_wrapper variable, and then compared them, and it works well.
However, If I change…
Eunho Choi
- 167
- 6
3
votes
2 answers
Best viable overloaded function between std::reference_wrapper and T
Recently, I've decided to write a class storing a variant with reference_wrapper and vector for having a choice either to own the value or having only a reference of it. That is, std::variant, reference_wrapper
koleydoscope
- 31
- 2
3
votes
1 answer
std::reference_wrapper v.s. int&
I was trying out the std::reference_wrapper with the following snippet
int a = 42, b = 52;
std::tuple> t = std::make_tuple(std::ref(a));
std::get<0>(t) = b;
std::cout << "t[0] = " << std::get<0>(t) << ", a = " << a << ",…
hsiu
- 88
- 5