How Are Move Constructors and Assignment Operators Implicitly Generated in C ?

Implicit Generation of Move Operations in C

In early drafts of the C 11 standard, there was a debate regarding the implicit generation of move constructors and assignment operators. This was due to concerns about potential performance implications and the desire to provide more control to programmers over these operations.

Current Specification

The current specification (N3225) states that move constructors and assignment operators will be implicitly declared as defaulted if:

• The class does not have a user-defined copy constructor
• The class does not have a user-defined copy assignment operator
• The class does not have a user-defined move assignment operator
• The class does not have a user-defined destructor
• The move constructor would not be implicitly defined as deleted

Addressing the Issue

While the default behavior has changed over time, there are several ways to address the lack of implicit move operations in older compilers:

• Manually Implement Move Constructors/Assignment Operators: This is the most straightforward approach, but it requires additional code and can be error-prone if not implemented correctly.
• Use a Macro: Macros can be used to automatically generate move constructors and assignment operators. For example, GManNickG's answer provides a macro that can be used for this purpose.
• Consider a C 11 Compliant Compiler: If possible, upgrade to a compiler that supports the implicit generation of move operations according to the current C 11 specification.

Additional Considerations

It's important to note that implementing move semantics eliminates the need for a swap member function. Additionally, the move constructor and assignment operator should only be used when the class manages its own resources, such as dynamically allocated memory. For classes that solely contain POD types and STL containers, the default copy semantics are usually sufficient.

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