1//===- LogicalResult.h - Utilities for handling success/failure -*- C++ -*-===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8
9#ifndef LLVM_SUPPORT_LOGICALRESULT_H
10#define LLVM_SUPPORT_LOGICALRESULT_H
11
12#include <cassert>
13#include <optional>
14
15namespace llvm {
16/// This class represents an efficient way to signal success or failure. It
17/// should be preferred over the use of `bool` when appropriate, as it avoids
18/// all of the ambiguity that arises in interpreting a boolean result. This
19/// class is marked as NODISCARD to ensure that the result is processed. Users
20/// may explicitly discard a result by using `(void)`, e.g.
21/// `(void)functionThatReturnsALogicalResult();`. Given the intended nature of
22/// this class, it generally shouldn't be used as the result of functions that
23/// very frequently have the result ignored. This class is intended to be used
24/// in conjunction with the utility functions below.
25struct [[nodiscard]] LogicalResult {
26public:
27 /// If isSuccess is true a `success` result is generated, otherwise a
28 /// 'failure' result is generated.
29 static LogicalResult success(bool IsSuccess = true) {
30 return LogicalResult(IsSuccess);
31 }
32
33 /// If isFailure is true a `failure` result is generated, otherwise a
34 /// 'success' result is generated.
35 static LogicalResult failure(bool IsFailure = true) {
36 return LogicalResult(!IsFailure);
37 }
38
39 /// Returns true if the provided LogicalResult corresponds to a success value.
40 constexpr bool succeeded() const { return IsSuccess; }
41
42 /// Returns true if the provided LogicalResult corresponds to a failure value.
43 constexpr bool failed() const { return !IsSuccess; }
44
45private:
46 LogicalResult(bool IsSuccess) : IsSuccess(IsSuccess) {}
47
48 /// Boolean indicating if this is a success result, if false this is a
49 /// failure result.
50 bool IsSuccess;
51};
52
53/// Utility function to generate a LogicalResult. If isSuccess is true a
54/// `success` result is generated, otherwise a 'failure' result is generated.
55inline LogicalResult success(bool IsSuccess = true) {
56 return LogicalResult::success(IsSuccess);
57}
58
59/// Utility function to generate a LogicalResult. If isFailure is true a
60/// `failure` result is generated, otherwise a 'success' result is generated.
61inline LogicalResult failure(bool IsFailure = true) {
62 return LogicalResult::failure(IsFailure);
63}
64
65/// Utility function that returns true if the provided LogicalResult corresponds
66/// to a success value.
67inline bool succeeded(LogicalResult Result) { return Result.succeeded(); }
68
69/// Utility function that returns true if the provided LogicalResult corresponds
70/// to a failure value.
71inline bool failed(LogicalResult Result) { return Result.failed(); }
72
73/// This class provides support for representing a failure result, or a valid
74/// value of type `T`. This allows for integrating with LogicalResult, while
75/// also providing a value on the success path.
76template <typename T> class [[nodiscard]] FailureOr : public std::optional<T> {
77public:
78 /// Allow constructing from a LogicalResult. The result *must* be a failure.
79 /// Success results should use a proper instance of type `T`.
80 FailureOr(LogicalResult Result) {
81 assert(failed(Result) &&
82 "success should be constructed with an instance of 'T'");
83 }
84 FailureOr() : FailureOr(failure()) {}
85 FailureOr(T &&Y) : std::optional<T>(std::forward<T>(Y)) {}
86 FailureOr(const T &Y) : std::optional<T>(Y) {}
87 template <typename U,
88 std::enable_if_t<std::is_constructible<T, U>::value> * = nullptr>
89 FailureOr(const FailureOr<U> &Other)
90 : std::optional<T>(failed(Other) ? std::optional<T>()
91 : std::optional<T>(*Other)) {}
92
93 operator LogicalResult() const { return success(has_value()); }
94
95private:
96 /// Hide the bool conversion as it easily creates confusion.
97 using std::optional<T>::operator bool;
98 using std::optional<T>::has_value;
99};
100
101/// Wrap a value on the success path in a FailureOr of the same value type.
102template <typename T,
103 typename = std::enable_if_t<!std::is_convertible_v<T, bool>>>
104inline auto success(T &&Y) {
105 return FailureOr<std::decay_t<T>>(std::forward<T>(Y));
106}
107
108/// This class represents success/failure for parsing-like operations that find
109/// it important to chain together failable operations with `||`. This is an
110/// extended version of `LogicalResult` that allows for explicit conversion to
111/// bool.
112///
113/// This class should not be used for general error handling cases - we prefer
114/// to keep the logic explicit with the `succeeded`/`failed` predicates.
115/// However, traditional monadic-style parsing logic can sometimes get
116/// swallowed up in boilerplate without this, so we provide this for narrow
117/// cases where it is important.
118///
119class [[nodiscard]] ParseResult : public LogicalResult {
120public:
121 ParseResult(LogicalResult Result = success()) : LogicalResult(Result) {}
122
123 /// Failure is true in a boolean context.
124 constexpr explicit operator bool() const { return failed(); }
125};
126} // namespace llvm
127
128#endif // LLVM_SUPPORT_LOGICALRESULT_H
129

source code of llvm/include/llvm/Support/LogicalResult.h