A situation arises in C++ where a compiler-generated special member function (such as a copy constructor, copy assignment operator, move constructor, or move assignment operator) is not automatically created by the compiler. This occurs when the synthesized default implementation would result in code that is either syntactically incorrect or semantically invalid according to the language’s rules. For example, if a class contains a member that cannot be copied or moved (perhaps a reference member or a const member without a user-defined assignment operator), the compiler will not generate the corresponding copy or move operation.
The implicit deletion of these functions is a crucial aspect of C++’s type safety and resource management. It prevents the creation of objects with undefined or erroneous states. By suppressing the default generation, the language forces the programmer to explicitly define the desired behavior, ensuring that objects are correctly constructed, copied, moved, and destroyed. Historically, this mechanism has evolved to provide greater control over object lifetime and value semantics, ultimately leading to more robust and predictable software.
