ScopedValue.Carrier (Java SE 23 & JDK 23)
Description: declaration: module: java.base, package: java.lang, class: ScopedValue, class: Carrier
Keywords: java.lang.ScopedValue.Carrier class

# Class ScopedValue.Carrier

java.lang.Object
java.lang.ScopedValue.Carrier

Enclosing class:
  `ScopedValuePREVIEW<T>`

public static final class ScopedValue.Carrier extends Object
`Carrier` is a preview API of the Java platform.
Programs can only use `Carrier` when preview features are enabled.
Preview features may be removed in a future release, or upgraded to permanent features of the Java platform.
A mapping of scoped values, as keys, to values.

A `Carrier` is used to accumulate mappings so that an operation (a `Runnable` or `ScopedValue.CallableOp`PREVIEW) can be executed with all scoped values in the mapping bound to values. The following example runs an operation with `k1` bound (or rebound) to `v1`, and `k2` bound (or rebound) to `v2`.

        ScopedValue.where(k1, v1).where(k2, v2).run(() -> ... );

A `Carrier` is immutable and thread-safe. The `where` method returns a new `Carrier` object, it does not mutate an existing mapping.

Unless otherwise specified, passing a `null` argument to a method in this class will cause a `NullPointerException` to be thrown.

Since:
  21

- ## Method Summary

  Modifier and Type
  Method
  Description
  `<R, X extends Throwable>
  R`
  `call(ScopedValue.CallableOpPREVIEW<? extends R,X> op)`
  Calls a value-returning operation with each scoped value in this mapping bound to its value in the current thread.
  `<T> T`
  `get(ScopedValuePREVIEW<T> key)`
  Returns the value of a `ScopedValue`PREVIEW in this mapping.
  `void`
  `run(Runnable op)`
  Runs an operation with each scoped value in this mapping bound to its value in the current thread.
  `<T> ScopedValue.CarrierPREVIEW`
  `where(ScopedValuePREVIEW<T> key, T value)`
  Returns a new `Carrier` with the mappings from this carrier plus a new mapping from `key` to `value`.

  ### Methods declared in class java.lang.Object

  `clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

- ## Method Details

  - ### where

    public <T> ScopedValue.CarrierPREVIEW where(ScopedValuePREVIEW<T> key, T value)
    Returns a new `Carrier` with the mappings from this carrier plus a new mapping from `key` to `value`. If this carrier already has a mapping for the scoped value `key` then it will map to the new `value`. The current carrier is immutable, so it is not changed by this method.
    Type Parameters:
      `T` - the type of the value
    Parameters:
      `key` - the `ScopedValue` key
      `value` - the value, can be `null`
    Returns:
      a new `Carrier` with the mappings from this carrier plus the new mapping

  - ### get

    public <T> T get(ScopedValuePREVIEW<T> key)
    Returns the value of a `ScopedValue`PREVIEW in this mapping.
    Type Parameters:
      `T` - the type of the value
    Parameters:
      `key` - the `ScopedValue` key
    Returns:
      the value
    Throws:
      `NoSuchElementException` - if the key is not present in this mapping

  - ### call

    public <R, X extends Throwable> R call(ScopedValue.CallableOpPREVIEW<? extends R,X> op) throws X
    Calls a value-returning operation with each scoped value in this mapping bound to its value in the current thread. When the operation completes (normally or with an exception), each scoped value in the mapping will revert to being unbound, or revert to its previous value when previously bound, in the current thread. If `op` completes with an exception then it propagated by this method.

    Scoped values are intended to be used in a structured manner. If code invoked directly or indirectly by the operation creates a `StructuredTaskScope`PREVIEW but does not closePREVIEW it, then it is detected as a structure violation when the operation completes (normally or with an exception). In that case, the underlying construct of the `StructuredTaskScope` is closed and `StructureViolationException`PREVIEW is thrown.

    Type Parameters:
      `R` - the type of the result of the operation
      `X` - type of the exception thrown by the operation
    Parameters:
      `op` - the operation to run
    Returns:
      the result
    Throws:
      `StructureViolationExceptionPREVIEW` - if a structure violation is detected
      `X` - if `op` completes with an exception
    Since:
      23
    See Also:
      - `ScopedValue.callWhere(ScopedValue, Object, CallableOp)`PREVIEW

  - ### run

    public void run(Runnable op)
    Runs an operation with each scoped value in this mapping bound to its value in the current thread. When the operation completes (normally or with an exception), each scoped value in the mapping will revert to being unbound, or revert to its previous value when previously bound, in the current thread. If `op` completes with an exception then it propagated by this method.

    Scoped values are intended to be used in a structured manner. If code invoked directly or indirectly by the operation creates a `StructuredTaskScope`PREVIEW but does not closePREVIEW it, then it is detected as a structure violation when the operation completes (normally or with an exception). In that case, the underlying construct of the `StructuredTaskScope` is closed and `StructureViolationException`PREVIEW is thrown.

    Parameters:
      `op` - the operation to run
    Throws:
      `StructureViolationExceptionPREVIEW` - if a structure violation is detected
    See Also:
      - `ScopedValue.runWhere(ScopedValue, Object, Runnable)`PREVIEW