Struct: TResult

template <typename T, typename E>
struct TResult;

Result type that can wrap either T value or E error data.

Useful for return types in functions that can return either valid value or some error. Given implementation tries to match TOptional API as much as possible.

Example

UENUM()
enum class EGuessError : uint8
{
	TooHigh,
	TooLow,
};

USTRUCT()
struct FShiaTheSecretKeeper
{
	GENERATED_BODY()

public:
	FShiaTheSecretKeeper() : Secret(), Password()
	{
	}

	FShiaTheSecretKeeper(FString InSecret, int InPassword) : Secret(InSecret), Password(InPassword)
	{
	}

	TResult<FString, EGuessError> TryGuess(int GuessPassword)
	{
		if (GuessPassword == this->Password)
		{
			return TResult<FString, EGuessError>(this->Secret);
		}
		else if (GuessPassword < this->Password)
		{
			return TResult<FString, EGuessError>(EGuessError::TooLow);
		}
		else
		{
			return TResult<FString, EGuessError>(EGuessError::TooHigh);
		}
	}

private:
	FString Secret = {};
	int Password = {};
};

int Main()
{
	const auto Shia = FShiaTheSecretKeeper("Just do it!", 42);
	const auto Result = Shia.TryGuess(42);
	if (Result.IsOk())
	{
		UE_LOG(LogTemp, Info, TEXT("Guessed! Secret: %s"), *Result.GetOk());
	}
	else
	{
		switch (Result.GetError())
		{
			case EGuessError::TooHigh:
				UE_LOG(LogTemp, Error, TEXT("Too high!"));
				break;

			case EGuessError::TooLow:
				UE_LOG(LogTemp, Error, TEXT("Too low!"));
				break;
		}
	}
}

Methods

• AsError

  public:
  TOptional<E> AsError() const;
  

  ---

  Returns option with cloned error data.

  In case of result wrapping value data, it returns none.

• AsOk

  public:
  TOptional<T> AsOk() const;
  

  ---

  Returns option with cloned value data.

  In case of result wrapping error data, it returns none.

• GetError

  public:
  E& GetError();
  

  ---

  Returns reference to internal error.

  Note

  It panics if result wraps value data.

• GetError

  public:
  const E& GetError() const;
  

  ---

  Returns reference to internal error.

  Note

  It panics if result wraps value data.

• GetOk

  public:
  T& GetOk();
  

  ---

  Returns reference to internal value.

  Note

  It panics if result wraps error data.

• GetOk

  public:
  const T& GetOk() const;
  

  ---

  Returns reference to internal value.

  Note

  It panics if result wraps error data.

• IsError

  public:
  bool IsError() const;
  

  ---

  Tells if result wraps error data.

• IsOk

  public:
  bool IsOk() const;
  

  ---

  Tells if result wraps value data.

• SetError

  public:
  void SetError(
      const E& Error
  );
  

  ---

  Replaces internal data with cloned error data.

  ---

  Arguments

  • Error

    const E& Error
    

    Error to copy from.

• SetError

  public:
  void SetError(
      E&& Error
  );
  

  ---

  Replaces internal data with moved error data.

  ---

  Arguments

  • Error

    E&& Error
    

    Error to consume.

• SetOk

  public:
  void SetOk(
      const T& Value
  );
  

  ---

  Replaces internal data with cloned value data.

  ---

  Arguments

  • Value

    const T& Value
    

    Value to copy from.

• SetOk

  public:
  void SetOk(
      T&& Value
  );
  

  ---

  Replaces internal data with moved value data.

  ---

  Arguments

  • Value

    T&& Value
    

    Value to consume.

• TResult

  public:
  TResult(
      const T& Value
  );
  

  ---

  Copy constructor.

  ---

  Arguments

  • Value

    const T& Value
    

    Value data to copy from.

• TResult

  public:
  TResult(
      T&& Value
  );
  

  ---

  Move constructor.

  ---

  Arguments

  • Value

    T&& Value
    

    Value to consume.

• TResult

  public:
  TResult(
      const E& Error
  );
  

  ---

  Copy constructor.

  ---

  Arguments

  • Error

    const E& Error
    

    Error to copy from.

• TResult

  public:
  TResult(
      E&& Error
  );
  

  ---

  Move constructor.

  ---

  Arguments

  • Error

    E&& Error
    

    Error to consume.

• TResult

  public:
  TResult(
      const TResult& Other
  );
  

  ---

  Copy constructor.

  ---

  Arguments

  • Other

    const TResult& Other
    

    Result to copy from.

• TResult

  public:
  TResult(
      TResult&& Other
  );
  

  ---

  Move constructor.

  ---

  Arguments

  • Other

    TResult&& Other
    

    Result to consume.

• operator bool

  public:
  explicit operator bool() const;
  

  ---

  Cast to boolean.

  Handy shortcut for TResult::IsOk. Useful when used in if statement condition.

• operator!=

  public:
  bool operator!=(
      const TResult& Lhs,
      const TResult& Rhs
  );
  

  ---

  Tells if two results aren't equal.

  Two results must both wrap either value or error, and if they do then their data is compared.

  ---

  Arguments

  • Lhs

    const TResult& Lhs
    

  • Rhs

    const TResult& Rhs
    

• operator<<

  public:
  FArchive& operator<<(
      FArchive& Ar,
      TResult& Result
  );
  

  ---

  Serializes given result.

  ---

  Arguments

  • Ar

    FArchive& Ar
    

  • Result

    TResult& Result
    

• operator=

  public:
  TResult& operator=(
      const TResult& Other
  );
  

  ---

  Copies other result.

  ---

  Arguments

  • Other

    const TResult& Other
    

    Result to copy from.

• operator=

  public:
  TResult& operator=(
      TResult&& Other
  );
  

  ---

  Consumes other result.

  ---

  Arguments

  • Other

    TResult&& Other
    

    Result to consume.

• operator=

  public:
  TResult& operator=(
      const T& Value
  );
  

  ---

  Replaces internal data with cloned value data.

  ---

  Arguments

  • Value

    const T& Value
    

    Value to copy from.

• operator=

  public:
  TResult& operator=(
      T&& Value
  );
  

  ---

  Replaces internal data with moved value data.

  ---

  Arguments

  • Value

    T&& Value
    

    Value to consume.

• operator=

  public:
  TResult& operator=(
      const E& Error
  );
  

  ---

  Replaces internal data with cloned error data.

  ---

  Arguments

  • Error

    const E& Error
    

    Error to copy from.

• operator=

  public:
  TResult& operator=(
      E&& Error
  );
  

  ---

  Replaces internal data with cloned error data.

  ---

  Arguments

  • Error

    E&& Error
    

    Error to consume.

• operator==

  public:
  bool operator==(
      const TResult& Lhs,
      const TResult& Rhs
  );
  

  ---

  Tells if two results are equal.

  Two results must both wrap either value or error, and if they do then their data is compared.

  ---

  Arguments

  • Lhs

    const TResult& Lhs
    

  • Rhs

    const TResult& Rhs
    

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