Re: [boost] Proposed SG14 <system_error2> ready for feedback

On 02/28/18 23:10, Niall Douglas via Boost wrote:

7. `std::error_code` enforced its value to always be an `int`. This is problematic for coding systems which might use a `long` and implement coding namespaces within the extended number of bits, or for end users wishing to combine a code with a `void *` in order to transmit payload or additional context. As a result, `status_code` is templated to its domain, and the domain sets its type. A type erased edition of `status_code<D>` is available as `status_code<void>`, this is for obvious reasons non-copyable, non-movable and non-destructible.

A more useful type erased edition is `status_code` which is available if `D::value_type` is trivially copyable, `T` is an integral type, and `sizeof(T) >= sizeof(D::value_type)`. This lets you use `status_code` in all your public interfaces without restrictions. As a pointer to the original category is retained, and trivially copyable types may be legally copied by `memcpy()`, type erased status codes work exactly as normal, except that publicly it does not advertise its type.

While I do see the need for providing extensions, I am not sure if status_code<void> is useful given all its "non-" characteristics. Can you elaborate on its use-cases? I propose that the customizable status_code<D> is renamed to basic_status_code<D>. In keeping with the pre-established practices of std::error_code using int, I furthermore suggest that status_code becomes a non-templated alias for basic_status_code<int>.