LegacyMutex implementation, per this blog post: https://medium.com/@noahlittle199/thread-safety-with-mutex-in-swift-6-575e79f14386

Mutex.swift

import Foundation

final class LegacyMutex<Wrapped>: @unchecked Sendable {
	private var mutex = pthread_mutex_t()
	private var wrapped: Wrapped
	
	init(_ initialValue: Wrapped) {
		pthread_mutex_init(&mutex, nil)
		self.wrapped = initialValue
	}
	deinit {
		pthread_mutex_destroy(&mutex)
	}
	
	func withLock<R>(_ body: @Sendable (inout Wrapped) throws -> R) rethrows -> R {
		pthread_mutex_lock(&mutex)
		defer { pthread_mutex_unlock(&mutex) }
		return try body (&wrapped)
	}
}

How to use?

Here's property declaration:

private let currencyCode: LegacyMutex<String> = .init("CHF")

Reading the value:

let cc = self.currencyCode.withLock{ $0 }

Update the value:

currencyCode.withLock {
	$0 = "RSD"
}