docs/_docs/reference/error-codes/E223.md
This error occurs during capture checking when a capability reference is used inside a class or expression whose capture set does not include that reference.
Capture checking tracks which capabilities (such as mutable references or I/O handles) a piece of code may use.
When a class has a restricted capture set — either explicitly declared by inheriting scala.caps.Pure or implicitly by inheriting a pure type like java.lang.Exception — any references to capabilities outside that set are rejected.
Note: This error requires the experimental capture checking feature to be enabled.
trait Handle:
val id: String
trait PureParent extends caps.Pure
class Processor(val ctx: Handle^) extends PureParent // error
class ImplicitlyPure(ctx: Handle^) extends java.lang.Exception // error
def test(handle: Handle^) =
new PureParent:
val ctx = handle // error
val id = ctx.id
-- [E223] CaptureChecking Error: example.scala:5:20 ----------------------------
5 |class Processor(val ctx: Handle^) extends PureParent // error
| ^
|Reference `Processor.this.ctx` is not included in the allowed capture set {} of the self type of class Processor.
-- [E223] CaptureChecking Error: example.scala:7:21 ----------------------------
7 |class ImplicitlyPure(ctx: Handle^) extends java.lang.Exception // error
| ^
|Reference `ImplicitlyPure.this.ctx` is not included in the allowed capture set {} of the self type of class ImplicitlyPure.
-- [E223] CaptureChecking Error: example.scala:11:8 ----------------------------
11 | val ctx = handle // error
| ^^^^^^^^^^^^^^^^
|Reference `handle` of value ctx is not included in the allowed capture set {} of the self type of anonymous class Object with PureParent {...}.
Classes extending pure types cannot hold any references to capabilities. Restructure your code to either:
trait Handle:
val id: String
trait NonPureParrent
trait PureParent extends NonPureParrent, caps.Pure
class Processor(val ctx: Handle^) extends NonPureParrent
class ImplicitlyPure(ctx: Handle) extends java.lang.Exception
def test(handle: Handle^) =
new PureParent:
val id = handle.id