Clarify SwiftUI ViewModel state null semantics #268
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This applies the same change made to `state` in icerockdev#209 to `stateNullable` to prevent potential memory churn.
This simplifies code and cleans up call-site use, and makes it explicit when to use each helper. When your Kotlin ViewModel `StateFlow` has non-optional values, use the `state` helper in SwiftUI. When your `StateFlow` has an optional type and might have `null` values, use `stateNullable` in SwiftUI. Note: There isn't compiler help when deciding between `state` and `stateNullable` in SwiftUI. Choosing `state` where `stateNullable` is required will cause a runtime crash due to force unwrapping. Take care to use the correct helper.
When Kotlin/Native exports to Objective-C, all custom classes share a common `KotlinBase` interface (which implements `NSObject` and has `isEqual` available). We take advantage of this in order to add `state` and `stateNullable` helpers without requiring downstream users to define their own `equals` and `mappers`. This simplification makes the library slightly easier to use and perhaps a little more intuitive. Instead of forcing callers through `state(_:equals:mapper:)` for custom types, it's possible to just use the simpler `state(_)` helper.
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This simplifies code and cleans up call-site use, and makes it explicit when to use each helper. When your Kotlin ViewModel
StateFlowhas non-optional values, use thestatehelper in SwiftUI. When yourStateFlowhas an optional type and might havenullvalues, usestateNullablein SwiftUI.Note: There isn't compiler help when deciding between
stateandstateNullablein SwiftUI. ChoosingstatewherestateNullableis required will cause a runtime crash due to force unwrapping. Take care to use the correct helper.This PR also introduces
stateandstateNullablehelpers forKotlinBase. When Kotlin/Native exports to Objective-C, all custom classes share a commonKotlinBaseinterface (which implementsNSObjectand hasisEqualavailable).This simplification makes the library slightly easier to use and perhaps a little more intuitive. Instead of forcing callers through
state(_:equals:mapper:)for custom types and making them define their ownequalsandmapper, it's now possible to just use the simplerstate(_)helper.