name: unreal-engine-cpp-pro
description: Expert guide for Unreal Engine 5.x C++ development, covering UObject hygiene, performance patterns, and best practices.
risk: safe
source: self

Unreal Engine C++ Pro

This skill provides expert-level guidelines for developing with Unreal Engine 5 using C++. It focuses on writing robust, performant, and standard-compliant code.

When to Use

Use this skill when:
- Developing C++ code for Unreal Engine 5.x projects
- Writing Actors, Components, or UObject-derived classes
- Optimizing performance-critical code in Unreal Engine
- Debugging memory leaks or garbage collection issues
- Implementing Blueprint-exposed functionality
- Following Epic Games' coding standards and conventions
- Working with Unreal's reflection system (UCLASS, USTRUCT, UFUNCTION)
- Managing asset loading and soft references

Do not use this skill when:
- Working with Blueprint-only projects (no C++ code)
- Developing for Unreal Engine versions prior to 5.x
- Working on non-Unreal game engines
- The task is unrelated to Unreal Engine development

Core Principles

1. UObject & Garbage Collection:

   • Always use UPROPERTY() for UObject* member variables to ensure they are tracked by the Garbage Collector (GC).
   • Use TStrongObjectPtr<> if you need to keep a root reference outside of a UObject graph, but prefer addToRoot() generally.
   • Understand the IsValid() check vs nullptr. IsValid() handles pending kill state safely.

2. Unreal Reflection System:

   • Use UCLASS(), USTRUCT(), UENUM(), UFUNCTION() to expose types to the reflection system and Blueprints.
   • Minimize BlueprintReadWrite when possible; prefer BlueprintReadOnly for state that shouldn't be trampled by logic in UI/Level BPs.

3. Performance First:

   • Tick: Disable Ticking (bCanEverTick = false) by default. Only enable it if absolutely necessary. Prefer timers (GetWorldTimerManager()) or event-driven logic.
   • Casting: Avoid Cast<T>() in hot loops. Cache references in BeginPlay.
   • Structs vs Classes: Use F structs for data-heavy, non-UObject types to reduce overhead.

Naming Conventions (Strict)

Follow Epic Games' coding standard:

• Templates: Prefix with T (e.g., TArray, TMap).
• UObject: Prefix with U (e.g., UCharacterMovementComponent).
• AActor: Prefix with A (e.g., AMyGameMode).
• SWidget: Prefix with S (Slate widgets).
• Structs: Prefix with F (e.g., FVector).
• Enums: Prefix with E (e.g., EWeaponState).
• Interfaces: Prefix with I (e.g., IInteractable).
• Booleans: Prefix with b (e.g., bIsDead).

Common Patterns

1. Robust Component Lookup

Avoid GetComponentByClass in Tick. Do it in PostInitializeComponents or BeginPlay.

void AMyCharacter::PostInitializeComponents() {
    Super::PostInitializeComponents();
    HealthComp = FindComponentByClass<UHealthComponent>();
    check(HealthComp); // Fail hard in dev if missing
}

2. Interface Implementation

Use interfaces to decouple systems (e.g., Interaction system).

// Interface call check
if (TargetActor->Implements<UInteractable>()) {
    IInteractable::Execute_OnInteract(TargetActor, this);
}

3. Async Loading (Soft References)

Avoid hard references (UPROPERTY(EditDefaultsOnly) TSubclassOf<AActor>) for massive assets which force load orders. Use TSoftClassPtr or TSoftObjectPtr.

UPROPERTY(EditAnywhere, BlueprintReadWrite)
TSoftClassPtr<AWeapon> WeaponClassToLoad;

void AMyCharacter::Equip() {
    if (WeaponClassToLoad.IsPending()) {
        WeaponClassToLoad.LoadSynchronous(); // Or use StreamableManager for async
    }
}

Debugging

• Logging: Use UE_LOG with custom categories.
  cpp DEFINE_LOG_CATEGORY_STATIC(LogMyGame, Log, All); UE_LOG(LogMyGame, Warning, TEXT("Health is low: %f"), CurrentHealth);
• Screen Messages:
  cpp if (GEngine) GEngine->AddOnScreenDebugMessage(-1, 5.f, FColor::Red, TEXT("Died!"));
• Visual Logger: extremely useful for AI debugging. Implement IVisualLoggerDebugSnapshotInterface.

Checklist before PR

• [ ] Does this Actor need to Tick? Can it be a Timer?
• [ ] Are all UObject* members wrapped in UPROPERTY?
• [ ] Are hard references (TSubclassOf) causing load chains? Can they be Soft Ptrs?
• [ ] Did you clean up verified delegates in EndPlay?