Unreal Engine

## Garbage Collection - Raw pointers to UObjects get garbage collected — use `UPROPERTY()` to prevent - `UPROPERTY()` marks for GC tracking — without it, pointer becomes dangling - `TWeakObjectPtr` for optional references — doesn't prevent collection, check `IsValid()` - `NewObject<T>()` for UObjects — never raw `new`, GC won't track it ## UPROPERTY and UFUNCTION - `UPROPERTY()` required for Blueprint access — and for GC tracking - `UFUNCTION()` for Blueprint callable/events — also required for replication - `EditAnywhere` vs `VisibleAnywhere` — edit allows changes, visible is read-only - `BlueprintReadWrite` vs `BlueprintReadOnly` — controls Blueprint access level ## Actor Lifecycle - `BeginPlay` after all components initialized — safe to access components - Constructor runs on CDO (Class Default Object) — don't spawn actors or access world - `PostInitializeComponents` before BeginPlay — for component setup - `EndPlay` for cleanup — called on destroy and level transition ## Tick Performance - Disable tick when not needed — `PrimaryActorTick.bCanEverTick = false` - Use timers instead of tick + counter — `GetWorldTimerManager().SetTimer()` - Tick groups for ordering — `PrePhysics`, `DuringPhysics`, `PostPhysics` - Blueprint tick expensive — move hot logic to C++ ## Replication - Server is authority — clients request, server validates and replicates - `UPROPERTY(Replicated)` for variable sync — implement `GetLifetimeReplicatedProps` - `UFUNCTION(Server)` for client-to-server RPC — must be `Reliable` or `Unreliable` - `HasAuthority()` to check if server — before executing authoritative logic - `Role` and `RemoteRole` for network role checks — `ROLE_Authority` is server ## Asset References - Hard references load with parent — bloats memory, use for always-needed - Soft references (`TSoftObjectPtr`) load on demand — for optional or large assets - `LoadSynchronous()` or `AsyncLoad` for soft refs — don't access until loaded - Blueprint class references: `TSubclassOf<T>` — type-safe class selection ## Memory and Pointers - `TSharedPtr` for non-UObjects — reference counted, auto-deletes - `TUniquePtr` for exclusive ownership — can't copy, moves only - `MakeShared<T>()` for creation — single allocation for object and control block - Never mix raw `new/delete` with smart pointers — choose one pattern ## Common Mistakes - Accessing null actor in Blueprint — use `IsValid()` node before access - PIE (Play In Editor) vs packaged build differ — test shipping build - Hot reload corrupts Blueprints — close editor, build, reopen - `GetWorld()` null in constructor — world doesn't exist yet, use BeginPlay - Spawning in constructor crashes — defer to BeginPlay or later - `FString` for display, `FName` for identifiers — FName is hashed, faster comparison