Is there a way I can run an asynchronous batch class synchronously?

Question

I know, it should not be done. But theoretically is it possible?

Answer 1

Batchable logic are just normal methods. You can emulate Database.executeBatch using something like this:

public static void executeBatchSync(Database.Batchable<Object> batch, Type iterableType, Integer batchSize) {
    Iterable<Object> iterableObject = batch.start(null);
    Iterator<Object> iter = iterableObject.iterator();
    Object[] temp = (Object[])iterableType.newInstance();
    Integer size = 0;
    while(iter.hasNext()) {
        temp.add(iter.next());
        size++;
        if(size == batchSize) {
            batch.execute(null, temp);
            temp.clear();
            size = 0;
        }
    }
    if(!temp.isEmpty()) {
    batch.execute(null, temp);
    }
    batch.finish(null);
}

Which would be called using something like this:

Utils.executeBatchSync(new MyBatchable(), List<Account>.class, 200);

Note that you'll be subject to normal synchronous limits, but you'd be able to use the class directly. It would probably be better to have your Batchable class call a utility class/method, though, so you don't need to emulate the entire Batchable runtime.

Edit: Please note that there are some major issues with types, so you might have to fiddle with this code to make it run properly with certain data types, or possibly implement multiple variants based on the expected return type of the start method. As I stated above, it's better to have a utility class you can call directly from both the batch and wherever you want to run this logic (for example, a trigger), rather than try to implement this. This answer is mostly an answer to an academic question, rather than something you should implement in production.