Add AnyHashableSendable

Author: stephencelis

README.md

@@ -35,6 +35,7 @@ This library comes with a number of tools that make working with Swift concurren
 testable.
 
   * [`LockIsolated`](#lockisolated)
+  * [`AnyHashableSendable`](#anyhashablesendable)
   * [Streams](#streams)
   * [Tasks](#tasks)
   * [Serial execution](#serial-execution)
@@ -44,6 +45,11 @@ testable.
 The `LockIsolated` type helps wrap other values in an isolated context. It wraps the value in a 
 class with a lock, which allows you to read and write the value with a synchronous interface.
 
+### `AnyHashableSendable`
+
+The `AnyHashableSendable` type is a type-erased wrapper like `AnyHashable` that preserves the
+sendability of the underlying value.
+
 ### Streams
 
 The library comes with numerous helper APIs spread across the two Swift stream types:

Sources/ConcurrencyExtras/AnyHashableSendable.swift

@@ -0,0 +1,23 @@
+/// A type-erased hashable, sendable value.
+///
+/// A sendable version of `AnyHashable` that is useful in working around the limitation that an
+/// existential `any Hashable` does not conform to `Hashable`.
+public struct AnyHashableSendable: Hashable, Sendable {
+  public let base: any Hashable & Sendable
+
+  /// Creates a type-erased hashable, sendable value that wraps the given instance.
+  public init(_ base: some Hashable & Sendable) {
+    self.base = base
+  }
+
+  public static func == (lhs: Self, rhs: Self) -> Bool {
+    func open<T: Equatable>(_ lhs: T) -> Bool {
+      lhs == rhs as? T
+    }
+    return open(lhs)
+  }
+
+  public func hash(into hasher: inout Hasher) {
+    hasher.combine(base)
+  }
+}

Sources/ConcurrencyExtras/Documentation.docc/ConcurrencyExtras.md

@@ -236,6 +236,7 @@ need to make weaker assertions due to non-determinism, but can still assert on s
 ### Data races
 
 - ``LockIsolated``
+- ``AnyHashableSendable``
 
 ### Serial execution