On 10/27/2017 12:29 AM, Martin Sebor wrote: > > IMO, a good rule of thumb to follow in class design is to have > every class with any user-defined ctor either define a default > ctor that puts the object into a determinate state, or make > the default ctor inaccessible (or deleted in new C++ versions). > If there is a use case for leaving newly constructed objects > of a class in an uninitialized state that's an exception to > the rule that can be accommodated by providing a special API > (or in C++ 11, a defaulted ctor).
Yet another rule of thumb is to make classes that model built-in types behave as close to the built-in types as possible, making it easier to migrate between the custom types and the built-in types (and vice versa), to follow expectations, and to avoid pessimization around e.g., otherwise useless forcing initialization of such types in containers/arrays when you're going to immediately fill in the container/array with real values. BTW, there's a proposal for adding a wide_int class to C++20: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2017/p0539r1.html and I noticed: ~~~ 26.??.2.?? wide_integer constructors [numeric.wide_integer.cons] constexpr wide_integer() noexcept = default; Effects: A Constructs an object with undefined value. ~~~ Thanks, Pedro Alves
