1//===--- StringSwitch.h - Switch-on-literal-string Construct --------------===/
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/// \file
9/// This file implements the StringSwitch template, which mimics a switch()
10/// statement whose cases are string literals.
11///
12//===----------------------------------------------------------------------===/
13#ifndef LLVM_ADT_STRINGSWITCH_H
14#define LLVM_ADT_STRINGSWITCH_H
15
16#include "llvm/ADT/StringRef.h"
17#include "llvm/Support/ErrorHandling.h"
18#include <cassert>
19#include <cstring>
20#include <initializer_list>
21#include <optional>
22
23namespace llvm {
24
25/// A switch()-like statement whose cases are string literals.
26///
27/// The StringSwitch class is a simple form of a switch() statement that
28/// determines whether the given string matches one of the given string
29/// literals. The template type parameter \p T is the type of the value that
30/// will be returned from the string-switch expression. For example,
31/// the following code switches on the name of a color in \c argv[i]:
32///
33/// \code
34/// Color color = StringSwitch<Color>(argv[i])
35/// .Case("red", Red)
36/// .Case("orange", Orange)
37/// .Case("yellow", Yellow)
38/// .Case("green", Green)
39/// .Case("blue", Blue)
40/// .Case("indigo", Indigo)
41/// .Cases({"violet", "purple"}, Violet)
42/// .Default(UnknownColor);
43/// \endcode
44///
45/// When multiple matches are found, the value of the first match is returned.
46template<typename T, typename R = T>
47class StringSwitch {
48 /// The string we are matching.
49 const StringRef Str;
50
51 /// The pointer to the result of this switch statement, once known,
52 /// null before that.
53 std::optional<T> Result;
54
55public:
56 explicit StringSwitch(StringRef S)
57 : Str(S), Result() { }
58
59 StringSwitch(StringSwitch &&) = default;
60
61 // StringSwitch is not copyable.
62 StringSwitch(const StringSwitch &) = delete;
63
64 // StringSwitch is not assignable due to 'Str' being 'const'.
65 void operator=(const StringSwitch &) = delete;
66 void operator=(StringSwitch &&) = delete;
67
68 // Case-sensitive case matchers.
69 StringSwitch &Case(StringLiteral S, T Value) {
70 CaseImpl(S, Value);
71 return *this;
72 }
73
74 StringSwitch& EndsWith(StringLiteral S, T Value) {
75 if (!Result && Str.ends_with(Suffix: S)) {
76 Result = std::move(Value);
77 }
78 return *this;
79 }
80
81 StringSwitch& StartsWith(StringLiteral S, T Value) {
82 if (!Result && Str.starts_with(Prefix: S)) {
83 Result = std::move(Value);
84 }
85 return *this;
86 }
87
88 StringSwitch &Cases(std::initializer_list<StringLiteral> CaseStrings,
89 T Value) {
90 // Stop matching after the string is found.
91 for (StringLiteral S : CaseStrings)
92 if (CaseImpl(S, Value))
93 break;
94 return *this;
95 }
96
97 // Case-insensitive case matchers.
98 StringSwitch &CaseLower(StringLiteral S, T Value) {
99 CaseLowerImpl(S, Value);
100 return *this;
101 }
102
103 StringSwitch &EndsWithLower(StringLiteral S, T Value) {
104 if (!Result && Str.ends_with_insensitive(Suffix: S))
105 Result = std::move(Value);
106
107 return *this;
108 }
109
110 StringSwitch &StartsWithLower(StringLiteral S, T Value) {
111 if (!Result && Str.starts_with_insensitive(Prefix: S))
112 Result = std::move(Value);
113
114 return *this;
115 }
116
117 StringSwitch &CasesLower(std::initializer_list<StringLiteral> CaseStrings,
118 T Value) {
119 // Stop matching after the string is found.
120 for (StringLiteral S : CaseStrings)
121 if (CaseLowerImpl(S, Value))
122 break;
123 return *this;
124 }
125
126 [[nodiscard]] R Default(T Value) {
127 if (Result)
128 return std::move(*Result);
129 return Value;
130 }
131
132 /// Declare default as unreachable, making sure that all cases were handled.
133 [[nodiscard]] R DefaultUnreachable(
134 const char *Message = "Fell off the end of a string-switch") {
135 if (Result)
136 return std::move(*Result);
137 llvm_unreachable(Message);
138 }
139
140 [[nodiscard]] operator R() { return DefaultUnreachable(); }
141
142private:
143 // Returns true when a match is found. If `Str` matches the `S` argument,
144 // stores the result.
145 bool CaseImpl(StringLiteral S, T &Value) {
146 if (Result)
147 return true;
148
149 if (Str != S)
150 return false;
151
152 Result = std::move(Value);
153 return true;
154 }
155
156 // Returns true when a match is found. If `Str` matches the `S` argument
157 // (case-insensitive), stores the result.
158 bool CaseLowerImpl(StringLiteral S, T &Value) {
159 if (Result)
160 return true;
161
162 if (!Str.equals_insensitive(RHS: S))
163 return false;
164
165 Result = std::move(Value);
166 return true;
167 }
168};
169
170} // end namespace llvm
171
172#endif // LLVM_ADT_STRINGSWITCH_H
173