From 24c800fb494fbee6e42bc156dc94232dc08971af Mon Sep 17 00:00:00 2001
From: George Barnett <gbarnett@apple.com>
Date: Wed, 24 Jul 2024 14:47:26 +0100
Subject: [PATCH] Change 'unsafeDowncast' to 'as!' (#186)

Motivation:

The 'unsafeDowncast' can cause a miscompile leading to unexpected
runtime behaviour.

Modifications:

- Use 'as!' instead

Result:

No miscompiles on 5.10
---
 Sources/ConcurrencyHelpers/Lock.swift | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/Sources/ConcurrencyHelpers/Lock.swift b/Sources/ConcurrencyHelpers/Lock.swift
index c3e3686..272a749 100644
--- a/Sources/ConcurrencyHelpers/Lock.swift
+++ b/Sources/ConcurrencyHelpers/Lock.swift
@@ -136,7 +136,8 @@ final class LockStorage<Value>: ManagedBuffer<Value, LockPrimitive> {
         let buffer = Self.create(minimumCapacity: 1) { _ in
             return value
         }
-        let storage = unsafeDowncast(buffer, to: Self.self)
+        // Avoid 'unsafeDowncast' as there is a miscompilation on 5.10.
+        let storage = buffer as! Self
 
         storage.withUnsafeMutablePointers { _, lockPtr in
             LockOperations.create(lockPtr)