package daml
Package Members
- package concurrent
A compatible layer for
scala.concurrent
with extra type parameters to controlExecutionContext
s.A compatible layer for
scala.concurrent
with extra type parameters to controlExecutionContext
s. Deliberately uses the same names as the equivalent concepts inscala.concurrent
.The trouble with sc.ExecutionContext is that it is used incoherently. This leads to the problems described in https://failex.blogspot.com/2020/05/global-typeclass-coherence-principles-3.html . The extension layer in this package adds a phantom type parameter to
ExecutionContext
and related types, so that types can be used to discriminate between ExecutionContexts at compile-time, and so Futures can declare which ExecutionContext their operations are in.For Scala 2.12, you must pass
-Xsource:2.13
to scalac for methods and conversions to be automatically found. You must alsoimport scalaz.syntax.bind._
or similar for Future methods likemap
,flatMap
, and so on.There are no constraints on the
EC
type variable; you need only declare types you wish to use for it that are sufficient for describing the domains in which you want ExecutionContexts to be discriminated. These types will never be instantiated, so you can simply declare that they exist. They can be totally separate, or have subtyping relationships; any subtyping relationships they have will be reflected in equivalent subtyping relationships between the resultingExecutionContext
s; if you declaresealed trait Elephant extends Animal
, then automaticallyExecutionContext[Elephant] <: ExecutionContext[Animal]
with scalac preferring the former when available (because it is "more specific"). They can even be singleton types, so you might usex.type
to suggest that the context is associated with the exact value of thex
variable.If you want to, say, refer to both sc.Future and concurrent.Future in the same file, we recommend importing *the containing package* with an alias rather than renaming each individual class you import. For example,
import com.daml.concurrent._ import scala.{concurrent => sc} // OR import scala.concurrent._ import com.daml.{concurrent => dc}
The exact name isn't important, but you should pick a short one that is sufficiently suggestive for you.
You should always be able to remove the substring
Of.Instance.T
from any inferred type; we strongly suggest doing this for clarity.Demonstrations of the typing behavior can be found in FutureSpec and ExecutionContextSpec. This library has no interesting runtime characteristics; you should think of it as exactly like
scala.concurrent
in that regard.