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Can’t wait to use lambdas to make new APIs? Get in line. Kotlin lets you specify a function as `inline` - which means calls will be replaced with the function body. Breathe and make lambda-based APIs with zero overhead. Docs: https://kotlinlang.org/docs/reference/inline-functions.html … #31DaysOfKotlinpic.twitter.com/mIKHA4i4K7

[2/2] Is the state of your enclosing class correct? Use `check` to verify. It will throw an IllegalStateException if the value checked is false. Doc: https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/check.html … #31DaysOfKotlinpic.twitter.com/ulPIe9JHWr

[1/2] Are your function arguments valid? Check before using them, with `require`. If they’re not valid an IllegalArgumentException is thrown. Doc: https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/require.html … #31DaysOfKotlinpic.twitter.com/0zafc2HbT0

In Android, onCreate or other callbacks initialize objects. In Kotlin non-null vals must be initialized. What to do? Enter `lateinit`. It's a promise: initialize me later! Use it to pinky-swear it will "eventually" be null safe Docs: https://kotlinlang.org/docs/reference/properties.html#late-initialized-properties-and-variables … #31DaysOfKotlinpic.twitter.com/wNLmLkM5cL

It’s good to be lazy! Defer the cost of expensive property initialization until they’re actually needed, by using `lazy`. The computed value is then saved and used for any future calls. Lazy: https://kotlinlang.org/docs/reference/delegated-properties.html#lazy … #31DaysOfKotlinpic.twitter.com/tlns367CVY

[3/3] Going further with RecyclerViews, if we have a lot of callbacks from a RecyclerView item, like this one with detail clicks, shares, and delete actions, we can use sealed classes. One callback taking one sealed class can handle all the things! #31DaysOfKotilnpic.twitter.com/TLw9H1B99n

[2/3] You can also use sealed classes in a RecyclerView adapter. They’re a perfect fit for ViewHolders - with a clean set of types to dispatch explicitly to each holder. Used as an expression, the compiler will error if all types aren’t matched. #31DaysOfKotlinpic.twitter.com/T63lnhCHfo

[1/3] Kotlin sealed classes let you easily handle error data. When combined with LiveData you can use one LiveData to represent both the success path and the error path. Way better than using two variables. Docs: https://kotlinlang.org/docs/reference/sealed-classes.html … #31DaysOfKotlinpic.twitter.com/KgqvwkgfPo

Is the number of method overloads getting out of hand? Specify default parameter values in functions. Make the code even more readable with named parameters. Doc: https://kotlinlang.org/docs/reference/functions.html#default-arguments … #31DaysOfKotlinpic.twitter.com/hcaXa3BB5D

In Kotlin, everything is public by default! Well, almost. Kotlin has a rich set of visibility modifiers you can use as well: private, protected, internal. Each of them reduces the visibility in a different way. Docs: https://kotlinlang.org/docs/reference/visibility-modifiers.html … #31DaysOfKotlinpic.twitter.com/e0zvulpOsj

The first #AndroidP developer preview highlights are here! Learn about changes to JobScheduler, #Kotlin execution, Image Decoding (with animation), WiFi Location, Dual Camera app support, and more. Watch the full video with @dagalpin → http://goo.gl/zes4wj pic.twitter.com/YFKFu89E07

Creating classes with one role: to hold data? Mark them as “data” classes. The default implementation of equals() is generated (so are hashCode(), toString(), and copy()) and checks for structural equality. Docs: https://kotlinlang.org/docs/reference/data-classes.html#data-classes … https://kotlinlang.org/docs/reference/equality.html … #31DaysOfKotlinpic.twitter.com/GK4R22l09N

In Kotlin, classes can have mutable and read-only properties, with getters and setters generated by default. You can also implement custom ones if required. Docs: https://kotlinlang.org/docs/reference/properties.html … #31DaysOfKotlinpic.twitter.com/moZccVna32