pre-sip about adding 'annotated imports' feature to scala language.

1. Annotated import
● SIP - ???
● http://bit.ly/TLZYKb
https://github.com/rssh/scala-annotated-import-example
●

2. Annotated import
● Problem:
– Imports not composable
– Set of implicit variables often configured through
import.
● Solution
– Allow annotations before import statement
– @exported import x._ => export x and all
exported imports inside one.

3. Problem Example:
File A
– import com.mongodb.casbah.Imports._
– import com.novus.salat._
– import com.mycompany.salatcontext._
– …..............
● File B
– import com.mongodb.casbah.Imports._
– import com.novus.salat._
– import com.novus.salat.global._
– ….................

4. Problem Example:
File A
– import com.mongodb.casbah.Imports._
– import com.novus.salat._
– import com.mycompany.salatcontext._
– …..............
● File B
– import com.mongodb.casbah.Imports._
– import com.novus.salat._
– import com.novus.salat.global._
– ….................

5. Proposed Solution
● Allow annotations before import
● @exported import X._
– Members of X
– @exported imports from X:

6. Application module config:
package object my.app
{
– @exported import all.required.libraries
– @exported import language._
– // disable some annotations
– class unchecked extends Annotation {}
}

7. Common usage patterns:
– Application writers:
● encapsulate all external dependencies in one package
object
– Library writers:
● Don't use, provide one module which application
writers will use.

8. Import via inheritance:
X <: Y =>
● should exported imports in X be visible in Y
trait X
{
@exported import something.Interesting
}
trait Y { .. use something.Interesting }

9. Import via inheritance
● PRO
– People actually emulate this approach by defining
aliases for imported methods in traits.
● CONTRA
– Complexity, ... impossible to disable simple.
● (provide own imports instead exported will work)

10. Implementation
● Compiler
– Core, Scaladoc, Tests,
– (new SIP-18 style implicit ?)
● Reflection
– Classfile format
– Symbols/Tree API

11. Implementation
● https://github.com/rssh/scala
– Branch annotated-import
● https://github.com/rssh/scala-annotated-import-exa
(scala-annotated-import-example)
● State
– Core : mostly done
– Scaladoc: in progress

12. What needed:
● Pre-SIP review
– http://bit.ly/TLZYKb
● Examples of usage
– (just fork scala-import-annotations-example)
● Welcome to hack.

13. Related things
● @deprecated import ....
– (add warning, should not be hard)
● @generated(generator) import
– Macros API ?

14. Thanks
● Ruslan Shevchenko
– https://github.com/rssh/
– ruslan@shevchenko.kiev.ua
– @rssh1