Elements of Kotlin Version 0.2 by Mark L. Murphy

Author:Mark L. Murphy
Language: eng
Format: mobi, epub
Publisher: CommonsWare
Published: 2019-08-04T19:14:50+00:00

Enums and Sealed Classes

A boolean is a way of modeling a fixed set of states, where there are only two possible states.

Frequently, though, we find ourselves needing to model a fixed set of states that has more than two entries. For example, even with something that is nominally a boolean, we might have “true”, “false”, and “undefined”. The latter state would be for cases where we have not yet gone through any code that positively sets the state to “true” or “false”. For example, for some sort of user preference, perhaps the user has not visited the “settings” screen to state their preference just yet, so their preference is “undefined”.

The more you look, the more you find that might be modeled this way:

The error responses from a server API

The steps in a wizard-style “signup” set of screens

The modes of transportation that a Person object might be taking (walking? biking? driving? flying? skiing? jet-skiing?)

And so on

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