Compile errors: 'AProjectileBase': undeclared identifier

[Frank_Engels]

I am getting these errors

 c:\users\engelsflm\documents\unreal projects\toontanks\source\toontanks\pawns\PawnBase.h(30) : error C2065: 'AProjectileBase': undeclared identifier
 c:\users\engelsflm\documents\unreal projects\toontanks\source\toontanks\pawns\PawnBase.h(30) : error C2923: 'TSubclassOf': 'AProjectileBase' is not a valid template type argument for parameter 'TClass'
  [2/10] PawnTank.cpp

And I could solve them when I add the following include:
#include "ToonTanks/Actors/ProjectileBase.h"
To the includes of PawnBase.h, but this include is not done in the course.

I do not get it?

Here is my code:
PawnBase.h

#pragma once

#include "CoreMinimal.h"
#include "GameFramework/Pawn.h"
#include "ToonTanks/Actors/ProjectileBase.h"
#include "PawnBase.generated.h"


class UCapsuleComponent;
class ProjectileBase;

UCLASS()
class TOONTANKS_API APawnBase : public APawn
{
	GENERATED_BODY()
private:
    //COMPONENTS
	UPROPERTY(VisibleAnywhere,BluePrintReadOnly, Category = "Components",meta = (AllowPrivateAccess = "true"))
	UCapsuleComponent* CapsuleComp;
	UPROPERTY(VisibleAnywhere,BluePrintReadOnly, Category = "Components",meta = (AllowPrivateAccess = "true"))
	UStaticMeshComponent* BaseMesh;
	UPROPERTY(VisibleAnywhere,BluePrintReadOnly, Category = "Components",meta = (AllowPrivateAccess = "true"))
	UStaticMeshComponent* TurretMesh;
	UPROPERTY(VisibleAnywhere,BluePrintReadOnly, Category = "Components",meta = (AllowPrivateAccess = "true"))
	USceneComponent* ProjectileSpawnPoint;
	//VARIABLES
    UPROPERTY(EditAnywhere, BluePrintReadOnly,Category = "Projectile type",meta = (AllowPrivateAccess = "true"))
	TSubclassOf<AProjectileBase> ProjectileClass;
public:
	// Sets default values for this pawn's properties
	APawnBase();

protected:
	
	void RotateTurret(FVector LookAtTarget);

	void Fire();

	virtual void HandleDestruction();




	
};

PawnBase.cpp

#include "PawnBase.h"
#include "Components/CapsuleComponent.h"
#include "ToonTanks/Actors/ProjectileBase.h"

// Sets default values
APawnBase::APawnBase()
{
 	// Set this pawn to call Tick() every frame.  You can turn this off to improve performance if you don't need it.
	PrimaryActorTick.bCanEverTick = true;

	CapsuleComp =  CreateDefaultSubobject<UCapsuleComponent>(TEXT("Capsule Collider"));
	RootComponent = CapsuleComp;

	BaseMesh = CreateDefaultSubobject<UStaticMeshComponent>(TEXT("Base Mesh"));
	BaseMesh->SetupAttachment(RootComponent);

	TurretMesh = CreateDefaultSubobject<UStaticMeshComponent>(TEXT("Turret Mesh"));
	TurretMesh->SetupAttachment(BaseMesh);

	ProjectileSpawnPoint = CreateDefaultSubobject<USceneComponent>(TEXT("Projectile Spawn Point"));
	ProjectileSpawnPoint->SetupAttachment(TurretMesh);
}

void APawnBase::RotateTurret(FVector LookAtTarget) 
{
	FVector LookAtTargetClean = FVector(LookAtTarget.X,LookAtTarget.Y,TurretMesh->GetComponentLocation().Z);
	FVector StartLocation = TurretMesh->GetComponentLocation();

	FRotator TurretRotation =FVector(LookAtTargetClean - StartLocation).Rotation();
	TurretMesh ->SetWorldRotation(TurretRotation);
}

void APawnBase::Fire() 
{
	if (ProjectileClass)
	{
		FVector SpawnLocation = ProjectileSpawnPoint->GetComponentLocation();
		FRotator SpawnRotation = ProjectileSpawnPoint->GetComponentRotation();
		
		AProjectileBase* TempProjectile = GetWorld()->SpawnActor<AProjectileBase>(ProjectileClass, SpawnLocation,SpawnRotation );
		TempProjectile->SetOwner(this);
	}	
}

void APawnBase::HandleDestruction() 
{
	// --- Universal functionality --- 
	// Play death effects particle, sound and camera shake. 

	// --- Then do Child overrides ---
	// -- PawnTurret - Inform GameMode Turret died -> Then Destroy() self. 

	// -- PawnTank - Inform GameMode Player died -> Then Hide() all components && stop movement input.

}

ProjectileBase.h

#pragma once

#include "CoreMinimal.h"
#include "GameFramework/Actor.h"
#include "ProjectileBase.generated.h"



class UProjectileMovementComponent;

UCLASS()
class TOONTANKS_API AProjectileBase : public AActor
{
	GENERATED_BODY()
private:
	UPROPERTY(VisibleAnywhere, BluePrintReadOnly, Category = "Components", meta = (AllowPrivateAccess = "true"))
	UProjectileMovementComponent* ProjectileMovement;
	UPROPERTY(VisibleAnywhere,BluePrintReadOnly, Category = "Components", meta = (AllowPrivateAccess = "true"))
	UStaticMeshComponent* ProjectileMesh;
	UPROPERTY(EditDefaultsOnly, Category = "Damage")
	TSubclassOf<UDamageType> DamageType;
	UPROPERTY(EditAnywhere,BluePrintReadOnly, Category = "Move", meta = (AllowPrivateAccess = "true"))
	float MovementSpeed = 1300.f;
	UPROPERTY(EditAnywhere,BluePrintReadOnly, Category = "Damage", meta = (AllowPrivateAccess = "true"))
	float Damage = 50;
	
public:	
	// Sets default values for this actor's properties
	AProjectileBase();

protected:
	// Called when the game starts or when spawned
	virtual void BeginPlay() override;



};

ProjectileBase.cpp

#include "ProjectileBase.h"
#include "Components/StaticMeshComponent.h"
#include "GameFramework/ProjectileMovementComponent.h"


// Sets default values
AProjectileBase::AProjectileBase()
{
 	// Set this actor to call Tick() every frame.  You can turn this off to improve performance if you don't need it.
	PrimaryActorTick.bCanEverTick = false;
	ProjectileMesh = CreateDefaultSubobject<UStaticMeshComponent>(TEXT("Projectile Mesh"));
	RootComponent = ProjectileMesh;
	
	ProjectileMovement = CreateDefaultSubobject<UProjectileMovementComponent>(TEXT("Projectile Movement"));
	ProjectileMovement->InitialSpeed =  MovementSpeed;
	ProjectileMovement-> MaxSpeed =  MovementSpeed;
	InitialLifeSpan = 3.0f;

}

// Called when the game starts or when spawned
void AProjectileBase::BeginPlay()
{
	Super::BeginPlay();
	
}

[Frank_Engels]

Found the problem.
The forward declaration of the Class in the PawnBase.h was wrong, I missed the A in front:

class ProjectileBase;

Should be:

class AProjectileBase;