Select in Objective-C

Objective-C doesn’t have built-in support for channels or select statements like Go does. However, we can simulate similar behavior using Grand Central Dispatch (GCD) and dispatch groups. Here’s an equivalent implementation:

#import <Foundation/Foundation.h>

int main(int argc, const char * argv[]) {
    @autoreleasepool {
        dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
        dispatch_group_t group = dispatch_group_create();
        
        // We'll use two dispatch_group_async calls to simulate two channels
        __block NSString *result1 = nil;
        __block NSString *result2 = nil;
        
        // Simulate the first "channel"
        dispatch_group_async(group, queue, ^{
            [NSThread sleepForTimeInterval:1.0];
            result1 = @"one";
            NSLog(@"received %@", result1);
        });
        
        // Simulate the second "channel"
        dispatch_group_async(group, queue, ^{
            [NSThread sleepForTimeInterval:2.0];
            result2 = @"two";
            NSLog(@"received %@", result2);
        });
        
        // Wait for both "channels" to complete
        dispatch_group_wait(group, DISPATCH_TIME_FOREVER);
        
        return 0;
    }
}

This program simulates the behavior of the original example using Grand Central Dispatch (GCD), which is Objective-C’s primary concurrency framework.

We create two asynchronous tasks using dispatch_group_async. Each task simulates a channel by sleeping for a specified duration and then setting a result.

Here’s a breakdown of the code:

1. We create a dispatch queue and a dispatch group. The queue will manage our concurrent tasks, and the group allows us to wait for all tasks to complete.

2. We define two block variables, result1 and result2, to store the results of our simulated channels.

3. We create two asynchronous tasks using dispatch_group_async. Each task sleeps for a specified duration (1 second for the first, 2 seconds for the second) and then sets its result.

4. We use NSLog to print each result as soon as it’s available, simulating the behavior of the select statement in the original code.

5. Finally, we use dispatch_group_wait to wait for both tasks to complete before the program exits.

To run this program:

1. Save the code in a file named Select.m.
2. Compile it using the following command:

$ clang -framework Foundation Select.m -o Select

3. Run the compiled program:

$ ./Select

The output will be similar to:

2023-06-01 12:34:56.789 Select[1234:56789] received one
2023-06-01 12:34:57.789 Select[1234:56789] received two

Note that the total execution time will be about 2 seconds, as both tasks run concurrently.

While this implementation doesn’t provide the exact same syntax as Go’s select statement, it achieves similar functionality in terms of waiting for multiple asynchronous operations and handling their results as they become available.