Good. Perhaps this is appropriate as a template for others.
On Wednesday, June 29, 2016 at 6:24:35 PM UTC-4, Yaakov Borstein wrote: > > > > On Monday, March 21, 2016 at 1:56:34 AM UTC+2, Jeffrey Sarnoff wrote: >> >> Redis itself is written in C. They document GET key: >> >>> Get the value of key. If the key does not exist the special value nil is >>> returned. >> >> An error is returned if the value stored at key is not a string, because >>> GET <http://redis.io/commands/get> only handles string values. >> >> >> digging deeper >> >>> The client library API should not return an empty string, but a nil >>> object, when the server replies with a Null Bulk String. >> >> For example a Ruby library should return 'nil' while a C library should >>> return NULL (or set a special flag in the reply object), and so forth. >> >> >> Single elements of an Array may be Null. This is used in Redis replies in >>> order to signal that this elements are missing and not empty strings. >> >> This can happen with the SORT command when used with the GET *pattern* >> option >>> when the specified key is missing. >> >> [For example, if the] second element is a Null. The client library >>> should return something like this: ["foo", nil, "bar"] >> >> >> The Redis *nil* indicates a non-present value (missing or unavailable or, >> not extant: a domain|-> range error). >> >> From a semiotic viewpoint, Julia's *nothing* is closer to "absence" than it >> is to "an absent value"; of course >> >> the operational machinery supplies an actual entity to be *nothing* (a >> singleton realization ofthe type Void). >> >> >> A much more contextual fit be the use of Nullable, although that may require >> more of the client; a simpler way >> >> to handle the Redis *nil* without doing something with *nothing* is to use a >> dedicated const symbol or a singleton >> >> to be that sentinel, perhaps: >> >> * const RedisNil = :RedisNil # or* >> >> *type RedisNIL end; RedisNil = RedisNIL()* >> >> >> *Somewhere there are lengthy and informative discussions about Julia and nil >> / NULL / nothing.* >> >> *(I noted this thread to the Redis.jl project).* >> >> >> >> >> >> >> >> On Sunday, March 20, 2016 at 6:45:57 PM UTC-4, jock....@gmail.com wrote: >>> >>> Redis.jl returns nothing when requesting a the value of a key that >>> doesn't exist: >>> >>> using Redis >>> conn = RedisConnection() >>> r = get(conn, "non_existent_key") >>> disconnect(conn) >>> r == nothing # true >>> >>> >>> On Sunday, March 20, 2016 at 1:31:30 AM UTC+11, Milan Bouchet-Valat >>> wrote: >>>> >>>> For now I don't know of a good solution to this pattern, but there's >>>> been some discussion about it: >>>> https://github.com/JuliaLang/julia/issues/15174 >>>> >>>> You should definitely use a Nullable instead of returning nothing. >>>> >>>> >>>> Regards >>>> >>>> Le samedi 19 mars 2016 à 02:58 -0700, Jeffrey Sarnoff a écrit : >>>> > You may be misusing nothing. It is unusual that a function would >>>> > return nothing some of the time and something other times. >>>> > Take a look at http://docs.julialang.org/en/latest/manual/faq/#nothin >>>> > gness-and-missing-values >>>> > If you have additional questions about this, please give an example >>>> > of what get_a(...) is getting and why it would be nothing some of the >>>> > time. >>>> > >>>> > > Hi All >>>> > > >>>> > > >>>> > > I found my self writing code like this a lot: >>>> > > >>>> > > x = get_a(...) >>>> > > >>>> > > if x != nothing >>>> > > y::A = x >>>> > > do_sth(y, ...) >>>> > > end >>>> > > >>>> > > In the above, I have to check for nothing first, and if it is not >>>> > > nothing, then I do a type assert to make sure the type is what I >>>> > > expected. >>>> > > >>>> > > Is there any function or macro in Julia that can help this? >>>> > > >>>> > > I know in F#, I have option.bind, so option.bind f x is equivalent >>>> > > to a pattern match: if x is None - > None; if x is something -> >>>> > > f(something) >>>> > > >>>> > > Also in C#, I have "customers?[0]?.Orders?.Count();" (as long as >>>> > > there is null before ?, it returns null immediately) >>>> > > >>>> > > Does Julia have something similar? >>>> > > >>>> > > >>> >>> > The latest merge resolves the issue of 'nil' in Redis.jl. >
