24 questions
6
votes
1
answer
199
views
Can move constructor with (const T&&) parameter be defaulted?
I see a similar question Default move constructor taking a const parameter, which is 8 years old, with the answer No.
But at the same time, a slightly modified program with the constructor defaulted ...
- 24.1k
4
votes
1
answer
159
views
Defaulting three way comparison operator in recursive data structures
I'd like to use a defaulted three-way comparison operator in a recursive data structure, like this:
struct MyStruct {
int i;
std::vector<MyStruct> v;
std::partial_ordering operator<=>...
- 4,898
2
votes
1
answer
126
views
Clarification about user-provided explicitly-defaulted function being implicitly defined as deleted
As per the document, which says that (emphasis mine):
A function is user-provided if it is user-declared and not explicitly
defaulted or deleted on its first declaration. A user-provided
explicitly-...
- 3,564
0
votes
1
answer
91
views
How to Check if a Constructor is Explicitly-Defaulted [closed]
For example:
struct X {
X(){/***/}
X(const int& ){/***/}
X( int&&){/***/}
X(const X& ) = default;
X( X&&) = default;
X& operator=(const X&...
- 655
8
votes
1
answer
141
views
Why can't most defaulted operators have a placeholder return type, i.e. auto?
C++20 has made it possible to default comparison operators, including the three-way comparison like this. <=> can have a deduced return type, but other operators can't:
struct S {
friend ...
- 43.3k
0
votes
0
answers
1k
views
error: use of deleted function operator=(&&) with std::optional
I got myself an error sprouting from std::optional. Now when trying to reconstruct it, there seems to be something going on with defaulted ctors that I don't yet understand. Consider the following ...
- 5,344
0
votes
1
answer
724
views
Declaration of operator has a different exception specifier
I am trying to "=default" my friend functions but keep getting the following error:
a4.cpp:180:17: error: declaration of ‘bool operator==(const playing_card&, const playing_card&) ...
- 25
2
votes
1
answer
195
views
Why does a defaulted default constructor depend on whether it is declared inside or outside of class?
In the following example, struct A does not have default constructor. So both struct B and struct C inherited from it cannot get compiler-generated default constructor:
struct A {
A(int) {}
};
...
- 24.1k
8
votes
1
answer
151
views
Can special member functions be defaulted if they use typedefs?
Clang compiles this fine, but GCC and MSVC complain that operator= cannot be defaulted:
#include <type_traits>
template<class T>
struct S
{
typedef typename std::enable_if<!std::...
- 212k
5
votes
1
answer
2k
views
Why C++20 allows defaulted comparison to compile even when it is deleted?
Consider the following code:
struct A {
};
struct B {
A a;
bool operator == (const B& other) const = default;
};
clang gives a nice warning :
warning: explicitly defaulted equality ...
- 30.9k
1
vote
2
answers
167
views
Why does copy-and-swap in a base class cause the copy-assignment operator to be implicitly deleted in the derived class?
Tested only in GCC and Clang, the presence of a pass-by-value copy assignment operator in the base class (useful when implementing the copy-and-swap (or copy-and-move) idiom) causes the copy ...
- 304
1
vote
1
answer
527
views
C++ implicit definition of special functions
In the current version of the C++ draft (september 2019), paragraph [class.default.ctor]/4 states:
A default constructor that is defaulted and not defined as deleted is implicitly defined when it is ...
- 1,981
7
votes
2
answers
394
views
Why is the constructor of std::in_place_t defaulted and explicit?
cppreference shows the following definition of std::in_place_t:
struct in_place_t {
explicit in_place_t() = default;
};
inline constexpr std::in_place_t in_place{};
Why have they added an ...
- 1,165
3
votes
3
answers
287
views
C++11 deleted/defaulted constructors
I'm a bit confused about how/why the constructors are called in C++11 and C++17.
#include <iostream>
using namespace std;
//---
template<typename T>
struct StructTest
{
public:
const ...
- 137
1
vote
2
answers
1k
views
What are the pros and cons of always declaring defaulted constructors?
What are the pro and cons of declaring always defaulted constructors for each non user-defined constructor?
Consider a class with a user-defined constuctor which does not need other user-defined ...
- 2,394