Stores values local to the current thread of execution meaning that each thread or process that accesses these values get to see their own copy. If the underlying platform does not support threading the practical effect of this class is no different than using a local value.

Setting a value is done by creating an instance of Contextual.Using, passing it the required value, or a function that will return the needed value when necessary, and passing it to a try-resource statement.

If a function is used to set the value then that value will be retrieved the moment the try-resource block is entered. If the same Using is re-used then the value will be refreshed by calling the function again.

When entering a try-resource block any previous value is stored and then restored at the end of the block so nested try-resource blocks are possible.

Retrieving the value is done using get(). Doing so when no try-resource statement is active will result in an assertion exception.

An example:

Contextual<String> stringValue = Contextual<String>();
Contextual<Integer> intValue = Contextual<Integer>();
try (stringValue.Using("foo"),
        intValue.Using(system.milliseconds)) {
    print(stringValue.get()); // prints "foo"
    print(intValue.get());    // prints the current time in ms
    try (stringValue.Using("bar")) {
        print(stringValue.get()); // prints "bar"
        print(intValue.get());    // prints same number as before
    }
}

NB: This example only shows how to use Contextual and does not show anything thread-related.