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kotlinlang

Why a separate `isInitialized` property instead of a null check? Is it to allow for initialization to a nullable value? (since `T` is allowed to be nullable)

It’s just so it covers some edge-cases. Theoretically, when the variable is lazily initialized, the initializer might do something and set variable to `null`. And then that initialization would happen every other time we reference it, since the value will again be `null`. This won’t happen if used correctly but with boolean we keep the implementation very precise. If you check the Kotlin source, they don’t use `isInitialized` but the property value is defined as `Any` and it holds some predefined object (`UNINITIALIZED_VALUE`), and then once it’s initialized, it will cast to `T` (<https://github.com/JetBrains/kotlin/blob/master/libraries/stdlib/src/kotlin/util/Lazy.kt#L76-L85>). For the sake of simplicity, I used boolean value.