ue5-cpp-gameplay

Quick Start

• Confirm target class type (AActor, UActorComponent, UObject, USaveGame, etc.).
• Define required Blueprint-facing API before implementation.
• Output both header and source files together.

API Anchors (UE5.6-UE5.8)

• Reflection and UObject anchors:
  • UCLASS, USTRUCT, UENUM, UINTERFACE, GENERATED_BODY()
  • UPROPERTY(...), UFUNCTION(...)
• Core gameplay type anchors:
  • AActor, UActorComponent, UDataAsset, UGameInstanceSubsystem
  • TObjectPtr<> in headers and TSubclassOf<> for class references
• Replication anchors:
  • GetLifetimeReplicatedProps(...)
  • DOREPLIFETIME(...) in Net/UnrealNetwork.h
  • ReplicatedUsing=OnRep_*, UFUNCTION(Server/Client/NetMulticast, ...)
• Gameplay tag anchors:
  • FGameplayTag, FGameplayTagContainer
  • explicit tag request/match checks with safe fallback behavior

Implementation Stage Contract

• Every gameplay C++ task must define:
  • Public header API surface (Blueprint/API visibility)
  • Private runtime implementation path (.cpp)
  • Ownership/lifetime model (constructor, init, teardown)
  • Network authority rules (single-player only or replicated flow)
  • Validation method (compile assumptions, usage examples, edge-case behavior)
• If any item is missing, the implementation spec is incomplete.

Workflow

1) Type and File Shape

• Create type declarations with Unreal macros and UE5 pointer conventions (TObjectPtr in headers).
• Produce paired .h and .cpp with forward declarations in header and concrete includes in source.
• Keep class responsibility narrow and reusable.

2) Public API Design

• Define Blueprint API (BlueprintCallable, BlueprintPure, categories, metadata) before implementation.
• Expose minimal callable surface; keep helper methods non-UFUNCTION unless needed.
• Declare clear input/output contracts and failure behavior.

3) Runtime Implementation

• Implement logic in .cpp with null checks, authority guards, and explicit branch behavior.
• Keep tick usage opt-in; prefer event-driven updates.
• Handle initialization order (BeginPlay, InitializeComponent, or subsystem init) explicitly.

4) Replication and RPC (When Needed)

• Add replicated properties and OnRep_* handlers only for true client-visible state.
• Register properties in GetLifetimeReplicatedProps(...) with DOREPLIFETIME(...).
• Use server-authoritative RPC entry points for client requests.

5) GameplayTags and Data-Driven Hooks

• Use FGameplayTag/FGameplayTagContainer with explicit tag names.
• Validate required tags at runtime and provide fallback for missing tags.
• Prefer DataAsset-driven config for tunables over hard-coded constants.

6) Validation Output

• Ensure output includes both files and required includes.
• Confirm Blueprint exposure, replication behavior, and error-handling paths are documented.
• Provide usage snippet or invocation flow when behavior is non-trivial.

Constraints

• Always provide matching .h and .cpp when creating a class.
• Use non-deprecated APIs compatible with UE5.6-UE5.8.
• Keep includes minimal; use forward declarations in headers.
• Avoid hardcoded asset paths unless explicitly requested.
• Prefer TObjectPtr<> in UPROPERTY object references in headers.
• Keep server-authoritative checks explicit for any network-affecting gameplay action.

Failure Handling

• Symptom: class compiles but is missing from Blueprint.
  • Locate: missing BlueprintType/Blueprintable/BlueprintCallable metadata.
  • Fix: add required reflection specifiers and regenerate project files/build.
• Symptom: unresolved symbol or include cycles.
  • Locate: header include graph and forward declaration misuse.
  • Fix: move heavy includes to .cpp, keep forward declarations in headers.
• Symptom: replicated property does not update on clients.
  • Locate: GetLifetimeReplicatedProps(...) and actor/component replication flags.
  • Fix: register with DOREPLIFETIME(...), ensure owning actor replicates.
• Symptom: OnRep_* never fires.
  • Locate: property write path and net role.
  • Fix: mutate on server authority path and verify property actually changes.
• Symptom: RPC callable but ignored at runtime.
  • Locate: RPC specifier and call site authority.
  • Fix: enforce client->server request path and server-side validation.
• Symptom: GameplayTag logic silently fails.
  • Locate: invalid tag names or missing tag config.
  • Fix: validate tags on startup and guard with explicit fallback behavior.

UE5.6-UE5.8 Compatibility Notes

• Reflection, replication, and GameplayTag APIs above are stable across UE5.6-UE5.8.
• Favor stable core APIs over editor-only helpers when runtime behavior is required.

Escalation

• Escalate when user asks for plugin/module-level refactor beyond a single gameplay class.
• Escalate when solution needs custom engine source modifications.