llvm/llvm/include/llvm/Support/LogicalResult.h

//===- LogicalResult.h - Utilities for handling success/failure -*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//

#ifndef LLVM_SUPPORT_LOGICALRESULT_H
#define LLVM_SUPPORT_LOGICALRESULT_H

#include <cassert>
#include <optional>

namespace llvm {
/// This class represents an efficient way to signal success or failure. It
/// should be preferred over the use of `bool` when appropriate, as it avoids
/// all of the ambiguity that arises in interpreting a boolean result. This
/// class is marked as NODISCARD to ensure that the result is processed. Users
/// may explicitly discard a result by using `(void)`, e.g.
/// `(void)functionThatReturnsALogicalResult();`. Given the intended nature of
/// this class, it generally shouldn't be used as the result of functions that
/// very frequently have the result ignored. This class is intended to be used
/// in conjunction with the utility functions below.
struct [[nodiscard]] LogicalResult { … };

/// Utility function to generate a LogicalResult. If isSuccess is true a
/// `success` result is generated, otherwise a 'failure' result is generated.
inline LogicalResult success(bool IsSuccess = true) { … }

/// Utility function to generate a LogicalResult. If isFailure is true a
/// `failure` result is generated, otherwise a 'success' result is generated.
inline LogicalResult failure(bool IsFailure = true) { … }

/// Utility function that returns true if the provided LogicalResult corresponds
/// to a success value.
inline bool succeeded(LogicalResult Result) { … }

/// Utility function that returns true if the provided LogicalResult corresponds
/// to a failure value.
inline bool failed(LogicalResult Result) { … }

/// This class provides support for representing a failure result, or a valid
/// value of type `T`. This allows for integrating with LogicalResult, while
/// also providing a value on the success path.
template <typename T> class [[nodiscard]] FailureOr : public std::optional<T> { … };

/// Wrap a value on the success path in a FailureOr of the same value type.
template <typename T,
          typename = std::enable_if_t<!std::is_convertible_v<T, bool>>>
inline auto success(T &&Y) { … }

/// This class represents success/failure for parsing-like operations that find
/// it important to chain together failable operations with `||`.  This is an
/// extended version of `LogicalResult` that allows for explicit conversion to
/// bool.
///
/// This class should not be used for general error handling cases - we prefer
/// to keep the logic explicit with the `succeeded`/`failed` predicates.
/// However, traditional monadic-style parsing logic can sometimes get
/// swallowed up in boilerplate without this, so we provide this for narrow
/// cases where it is important.
///
class [[nodiscard]] ParseResult : public LogicalResult { … };
} // namespace llvm

#endif // LLVM_SUPPORT_LOGICALRESULT_H