[swift-evolution] Beef up Imports

[Jordan Rose]

I'm (personally) not such a fan of saying "import just this one thing" or "import everything except this one thing"—you end up trying to use UIImage(named:), and then realizing you haven't imported any of the top-level names. But "import qualified" seems great to me, and "import Foo as Bar" also seems reasonable.

Jordan


> On Dec 28, 2015, at 16:47, Kevin Ballard via swift-evolution <swift-evolution at swift.org> wrote:
> 
> I like the idea here, but I'm not sold on the syntax. I also do explicitly want an `import qualified`. And with qualified imports, I question whether we really need to support renaming in the import syntax here.
>  
> I'm tempted to say we should just crib Haskell's import rules (https://wiki.haskell.org/Import <https://wiki.haskell.org/Import>), with the minor change that importing members by name still makes them accessible via the module name too (in Haskell `import Mod (x, y)` makes `x` and `y` visible but does not make `Mod.x` or `Mod.y` visible). This lets you say things like
>  
> import Mod // imports Mod and all its members
> import Mod () // only provides access to protocol conformances declared in Mod, doesn't actually import anything
> import Mod (x,y) // imports `x` and `y`, which are also accessible as e.g. `Mod.x`, but does not provide `z` or `Mod.z`
> import qualified Mod // imports Mod but all access to members has to go through it, e.g. `Mod.x`
> import qualified Mod (x,y) // imports Mod but only provides access to `Mod.x` and `Mod.y` but not e.g. `Mod.z`
> import Mod hiding (x,y) // imports Mod and its members except for `x` or `y`
> import qualified Mod hiding (x,y) // imports e.g. `Mod.z` but not `Mod.x` or `Mod.y`
> import Mod as Foo // imports Mod and renames the module to Foo, so e.g. `x` and `Foo.x` are accessible
> import Mod as Foo (x,y) // renames Mod to Foo, provides `x`, `y`, `Foo.x`, and `Foo.y`
> import qualified Mod as Foo // renames Mod to Foo, all members are accessible via the module e.g. `Foo.x`
> import qualified Mod as Foo (x,y) // renames Mod to Foo, provides access to `Foo.x` and `Foo.y` but not e.g. `Foo.z`
>  
> Furthermore, you can have multiple import statements from the same module, so you can say something like
>  
> import qualified Mod
> import Mod (x,y)
>  
> to provide access to all of Mod qualified with the name, and additionally import `x` and `y` as unqualified identifiers.
>  
> -Kevin Ballard
> 
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