The C++ "using namespace" and Julia "using module" are not quite the same thing. The C++ namespace is a top level entity that is created and initialized as part of the C++ startup code and the "using" just makes the names of these global entities available within the scope. The Julia "using" imports, and thus creates, the module for the first time, and Julia modules can contain statements that run at initialization, whereas C++ namespaces can only contain declarations.
But if the Julia "using" is within the function, when should the actual import and initialize and execute the statements be done? Every time the function is called is very expensive. Hoist the import out of the function to the top level, but doing this naively (ie putting the hoisted import just before the function) will then affect all code following the function Have a "pseudo" top- level visible only to the function adds a complete new complication to the name management code. But then what happens if the module is imported into two functions, how is its initialization managed? Or the top level and the function? So for now the "simpler is better" approach is to have the user manage importing at the top level only. Cheers Lex On Tuesday, March 3, 2015 at 7:23:33 AM UTC+10, Josh Langsfeld wrote: > > It's discussed in the FAQ so there must be a good reason for it, though no > rationale is mentioned. > > > http://docs.julialang.org/en/latest/manual/faq/#can-i-use-using-or-import-inside-a-function > > On Monday, March 2, 2015 at 3:00:21 PM UTC-5, Patrick O'Leary wrote: >> >> On Saturday, February 28, 2015 at 11:06:38 AM UTC-6, MA Laforge wrote: >>> >>> C++ provides "using namespace X" to "make available" the contents of X >>> to the current scope. This even works on un-named scopes within a function: >>> >> >> (etc.) >> >> I know this is something that's come up before, and I think rejected--I >> think because it causes conflicts with multiple dispatch? But I can't seem >> to find the thread(s). >> >> I can't create a hard conflict in a quick mental search for an example, >> but I can create some level of confusion: >> >> module Foo >> bar::Int = 1 >> end >> >> module Baz >> bar::Float64 = 27.3 >> with module Foo # not current Julia syntax >> bar #which bar is this? >> end >> end >> >
