Equivalent on Objective C/Swift of Java ThreadLocal Variables

Question

In Java, we have the ThreadLocal class:

This class provides thread-local variables. These variables differ from their normal counterparts in that each thread that accesses one (via its get or set method) has its own, independently initialized copy of the variable. ThreadLocal instances are typically private static fields in classes that wish to associate state with a thread (e.g., a user ID or Transaction ID).

Example:

private static final ThreadLocal<StringBuilderHelper>
    threadLocalStringBuilderHelper = new ThreadLocal<StringBuilderHelper>() {
        @Override
        protected StringBuilderHelper initialValue() {
            return new StringBuilderHelper();
        }
    };

Is there any equivalent in Objective C or Swift to simulate this behavior? Can i just use on Swift:

static let String = someInitialValue()

and achieve the same goal?

Answer 1

Have a look at NSThread threadDictionary. I believe this is roughly the same thing.

A typical use in Objective-C might be:

NSMutableDictionary *threadData = [[NSThread currentThread] threadDictionary];
threadData[someKey] = someObject; // write

someObject = threadData[someKey]; // read