Why Coders Use Interfaces

Going on a road trip with Auntie Pat Tern and cousin Tim Toady reveals a lot about them as only a road trip can. Tim was called a "whipper snapper" on more than one occasion for criticizing Auntie Pat Tern's driving. "I cannot wait for self-driving cars," he proclaimed while Auntie Pat Tern praised the freedom of the open road and the control she feels while driving a car. Which got me thinking about why interfaces are so important as part of my programming team's design decisions.

Tim Toady prefers to drive arcade games while Auntie Pat Tern craves a 64 1/2 mustang convertible. But they both drive reasonably well in the electric car they have at home and the gas guzzler we rented for our long drive. That's because the interface of gear shift, accelerator, brake, and steering wheel are universally well understood by users.

Accelerate, brake, steer, and shift.
The simplicity of a good interface.

That same interface translates inputs to a multitude of different systems from arcade games to tractor-trailer trucks. When it comes to deciding whether to accelerate or decelerate, the driver/user does not care if the vehicle is electric or gas-powered. A lot of people who drive electric cars even still say "gas pedal".

Autonomous driving vehicles use the same interface as people: shift, accelerate, brake, steer. By using the same interface, a person can take over in an emergency, or maybe just for the fun of driving.

Developers use good interfaces like this to future-proof their code. If the business rules are protected from the mechanism for inputting data thanks to a reliable interface, we can make sure the most important business rules continue to function as expected.

Sure, sometimes the interface has to change a bit with new business automations. When cars got automatic transmissions, the gear shift changed and we lost the clutch. The same happens with code, new automations require small changes to the programming interface, but the goal of an interface is to minimize the need for such changes. Ultimately, we want to put interfaces between systems to give ourselves flexibility to support new automation, like Tim Toady's self driving car, as easily as we support more manual systems, like Auntie Pat Tern's stick shift.