Progressive Disclosure In Swift

In his excellent interview with the Accidental Tech Podcast, Chris Lattner defended the goal of Swift being suitable to both beginner and advanced programmers. He cites progressive disclosure, a design philosophy that is often employed in GUI applications, to make otherwise intimidating interfaces appear approachable. From episode 205 of the show:

The secret to Swift in being easy to learn, easy to use as a teaching vehicle, but also powerful enough to solve the problems that need to be solved, is that the complexity in the language needs to be progressively disclosed.

This resonates particularly with me not only because I strive to make the same kinds of design tradeoffs in my own software, but because this concept is particularly important to the history of the Macintosh. Progressive disclosure as a user accommodation is intrinsic to most Mac and iOS interface design.

An example that anybody who uses a Mac can relate to is the process of deleting files by way of the Trash. There’s a file on your Desktop, and you want to get rid of it. A naive user who has never used a Mac before will soon learn how to drag the icon onto the trash, and how to empty it through a variety of discoverable UI buttons and menus. This is the Mac, it’s easy to use.

After gaining some experience the same user might start to find all that clicking and dragging tedious, so they’ll be delighted to learn that the cryptic symbols on commonly-used menu items represent keyboard shortcuts. To throw away a file and empty the trash, just select the file, press Cmd-Delete, and then Cmd-Shift-Delete. This is the Mac, it’s streamlined for productivity.

When the standard menu items and shortcuts don’t cut it anymore, the same user will be inspired by the variety of nuanced variations that are unlocked by holding the Option key while selecting menu items, and that the incorporation of the Option key into existing keyboard shortcuts often maps perfectly to the same menu item that appears when the key is held down. “Move to Trash” becomes “Delete Immediately,” and “Empty Trash…” becomes “Empty Trash”. The omission of the ellipsis, they have come to discover, indicates an action that will take place immediately, without additional interaction. This is the Mac, it’s kind of complicated, but great for power users.

Finally, finding cause to delete a variety of files from a directory selectively, based on pattern-matching, they discover the Terminal app. They teach themselves the basics of a decades old interactive shell scripting wildcard notation, and are off to the races invoking the “rm” tool with wild abandon. This is the Mac, it’s got god-awful, nasty interfaces for accomplishing just about anything.

I worked at Apple from around 1995 to 2002, so I had the pleasure of witnessing reaction both within and outside the company as we transitioned from Mac OS 9 to Mac OS X. The Terminal, as it happens, was one of the most contentious new features. Mac OS 9 had standalone command-line developer tools such as MPW (Macintosh Programmers Workshop), but it was a sort of point of pride that it didn’t ship with a Terminal app. This wasn’t DOS, for crying out loud! Many people complained that Mac OS X was too complicated, and that the inclusion of a Terminal app was the beginning of the end for the system’s famous usability.

Fifteen years later, people are still performing incredibly simple, incredibly complex tasks with macOS Sierra. It ships with a Terminal and it ships with a Trash icon. This is the Mac, it spans the spectrum from simplicity to complexity. Apple’s turns out to be pretty good at this, so they deserve the benefit of the doubt that they’ll achieve the same type of goal with Swift. It seems like they’re off to a good start.