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

» cpp » 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

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

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

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

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

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.