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On 04/12/2012 22:28, Dirk Laurie wrote:
2012/12/4 spir <denis.spir@gmail.com>:PS: The more I think at it, the more imposes itself the idea we need 2 nils: one "nullnil" for required data, meaning a real error, "too bad, missing, try again another day"; one "nonenil" for optional data, thus just meaning "not there!".The distinction between "none" and "nil" is available in the C API, with explicit equivalence only on request (lua_isnil, lua_isnone, lua_isnoneornil). In Lua itself, the idiom for customized missing data is a dedicated identifier, e.g. none = {} Do you have an application in mind where you are in Lua all the time and where the "none" idiom would not be sufficient?
no. Indeed, you are right, the solution you give is precisely the one I use when the distinction is _absolutely_ needed (because of semantic or practicle confusion). yes. Because "none-nil" does not exist in the language, noone ever makes the distinction, or nearly. And we get the confusion as well as real errors and sometimes difficult bugs.
I mean, in practice, the problems exist (I don't invent them, they're documented even in C++ with abuse of NULL for app-semantic meaning). And the distinction between required data and optional data also is real.
Denis