Monday, January 12, 2015 [Tweets] [Favorites]

Finite States of America

Soroush Khanlou:

The benefits of using state machines are myriad. First, explicitly storing the states and transitions that are valid in your system leaves fewer nooks and crannies for bugs to hide out in. It is said that bugs are just states that you haven’t defined yet. If your object is defined by four booleans, it can be in 16 different states, all of which require testing. Imagine how many states it can have with integers, or strings! A state machine limits the number of possible configurations your object can be in, and defines them formally.

Having all of the transitions in one place will help you see the user’s flow through the system. What happens if this step takes longer than expected? Clearly-defined transitions make it painfully obvious what happens if an event happens out of order. Since every transition flows through one point, it is trivial to log all of the transitions. You can use that information to determine how your object went off the rails.

Update (2015-01-13): Soroush Khanlou:

As awesome as state machines are, they can often be very high-ceremony to set up. A typical Objective-C library requires a lot of code to set up. I wanted to explore combining a few techniques from the this blog to try and make a low-ceremony state machine, one that doesn’t require setting up all of your states, transitions, and events ahead of time.

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