Quick Reference

| Topic | File |

|-------|------|

| Null safety operators and patterns | nullsafety.md |

| Coroutines, flows, structured concurrency | coroutines.md |

| Collections, sequences, data classes | collections.md |

| Scope functions, extensions, sealed classes | idioms.md |

| Java interop and common Kotlin mistakes | interop.md |

| Android lifecycle, Compose state | android.md |

| Delegation, inline, reified, multiplatform | advanced.md |

Critical Rules

!! asserts non-null — crashes on null, use only when you've already checked
Platform types from Java are risky — add null checks or use @Nullable/@NonNull annotations
Elvis with return/throw for early exit — val name = user?.name ?: return

viewModelScope auto-cancels on ViewModel clear — don't use GlobalScope in Android
Structured concurrency: child coroutine failure cancels parent — use supervisorScope to isolate
StateFlow needs initial value and never completes — SharedFlow for one-shot events
Inject dispatchers for testability — don't hardcode Dispatchers.IO

first() throws on empty — use firstOrNull() for safe access
Only constructor properties in equals/hashCode — body properties ignored
mutableStateListOf for Compose — wrapping mutableListOf in state won't track changes

Don't nest scope functions — readability drops fast, extract to named functions
Extensions are resolved statically — not polymorphic, receiver type matters at compile time

repeatOnLifecycle(STARTED) for flow collection — launchWhenStarted is deprecated
remember survives recomposition only — use rememberSaveable for config changes
collectAsStateWithLifecycle is the gold standard — lifecycle-aware + Compose state

== is structural equality in Kotlin — === for reference, opposite of Java
SAM conversion only for Java interfaces — Kotlin interfaces need explicit fun interface
@JvmStatic, @JvmOverloads, @JvmField for Java-friendly APIs