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What's difference between forward and move in the constructor of class?


What's difference between forward and move in the constructor of class?

By : user2183986
Date : November 17 2020, 04:01 AM
should help you out If val_t is not an lvalue reference type, then value in constructor is an rvalue reference, and std::forward is equivalent to std::move.
If val_t is an lvalue reference, then so is value. std::forward then returns an lvalue reference and the code compiles. std::move returns an rvalue reference, which cannot be bound to m_value (which is an lvalue reference), and compiler reports an error.
code :


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c++ vector implementation - move constructor - move vs forward

c++ vector implementation - move constructor - move vs forward


By : Amine Kh
Date : March 29 2020, 07:55 AM
seems to work fine Yes, for a type without reference qualifiers T, both std::forward and std::forward are just fancy ways of saying std::move.
Position/Order of move constructor within class matters? Templated cast operator in conjunction with move constructor

Position/Order of move constructor within class matters? Templated cast operator in conjunction with move constructor


By : Rakesh Yadav
Date : March 29 2020, 07:55 AM
With these it helps This looks like a compiler bug, but the case is so simple I am a bit skeptical, so I am looking for a confirmation. Reproducible with both VS2010 and VS2012. The below example does not compile. This error is given: , Your expression
code :
(OtherType<wstring>) ConvertibleToAny()
static_cast<OtherType<wstring>>(ConvertibleToAny())
OtherType<wstring> t(ConvertibleToAny())
ConvertibleToAny [temporary] -> int
ConvertibleToAny [temporary] -> OtherType<wstring> &&
Use a forward-declared class in a virtual function in a template baseclass where the constructor only needs the forward

Use a forward-declared class in a virtual function in a template baseclass where the constructor only needs the forward


By : Mars
Date : March 29 2020, 07:55 AM
may help you . First, as many have stated, the standard fully allows for compilers to instantiate (or chose not to instantiate) to their hearts content in this situation; by a strict interpretation of the standard, this is a code issue, not an MSVC bug. The behavior you are depending on is platform specific and therefore non-standard; while this is not a "bug" per se, it's distinctly non-portable.
However, it's interesting to understand why GCC and Clang differ from MSVC, which has to do with how vtables are set up in each compiler.
code :
class A : public B
C++11 constructor argument: std::move and value or std::forward and rvalue reference

C++11 constructor argument: std::move and value or std::forward and rvalue reference


By : Greg Rank
Date : March 29 2020, 07:55 AM
it helps some times The two variants differ in functionality. The following statements work for the second one–but not for the first one:
code :
Y y;
X x(y);
struct X
{
    Y data_;
    explicit X(const Y& data) : data_(data) { }
    explicit X(Y&& data) : data_(std::move(data)) { }
};

struct X
{
    Y data_;
    explicit X(Y data) : data_(std::move(data)) { }
};
"Use of undefined type" with unique_ptr to forward declared class and defaulted move constructor/assignment

"Use of undefined type" with unique_ptr to forward declared class and defaulted move constructor/assignment


By : B3r
Date : March 29 2020, 07:55 AM
seems to work fine Yes, you need to have access to the full definition of B from wherever you instanciate std::unique_ptr::~unique_ptr, because it needs to call B's destructor.
In your case, that means that A::~A's definition must be moved to a separate A.cpp file, which includes B.h.
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