StringSwitch.h revision 6c2a7a04da2a6c8829b82cecb355b718f350c4f1 
1//===--- StringSwitch.h - Switch-on-literal-string Construct --------------===/
2//
3//                     The LLVM Compiler Infrastructure
4//
5// This file is distributed under the University of Illinois Open Source
6// License. See LICENSE.TXT for details.
7//===----------------------------------------------------------------------===/
8//
9//  This file implements the StringSwitch template, which mimics a switch()
10//  statements 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 <cassert>
18#include <cstring>
19
20namespace llvm {
21
22/// \brief A switch()-like statement whose cases are string literals.
23///
24/// The StringSwitch class is a simple form of a switch() statement that
25/// determines whether the given string matches one of the given string
26/// literals. The template type parameter \p T is the type of the value that
27/// will be returned from the string-switch expression. For example,
28/// the following code switches on the name of a color in \c argv[i]:
29///
30/// \code
31/// Color color = StringSwitch<Color>(argv[i])
32///   .Case("red", Red)
33///   .Case("orange", Orange)
34///   .Case("yellow", Yellow)
35///   .Case("green", Green)
36///   .Case("blue", Blue)
37///   .Case("indigo", Indigo)
38///   .Cases("violet", "purple", Violet)
39///   .Default(UnknownColor);
40/// \endcode
41template<typename T>
42class StringSwitch {
43  /// \brief The string we are matching.
44  StringRef Str;
45
46  /// \brief The result of this switch statement, once known.
47  T Result;
48
49  /// \brief Set true when the result of this switch is already known; in this
50  /// case, Result is valid.
51  bool ResultKnown;
52
53public:
54  explicit StringSwitch(StringRef Str)
55  : Str(Str), ResultKnown(false) { }
56
57  template<unsigned N>
58  StringSwitch& Case(const char (&S)[N], const T& Value) {
59    if (!ResultKnown && N-1 == Str.size() &&
60        (std::memcmp(S, Str.data(), N-1) == 0)) {
61      Result = Value;
62      ResultKnown = true;
63    }
64
65    return *this;
66  }
67
68  template<unsigned N0, unsigned N1>
69  StringSwitch& Cases(const char (&S0)[N0], const char (&S1)[N1],
70                      const T& Value) {
71    return Case(S0, Value).Case(S1, Value);
72  }
73
74  template<unsigned N0, unsigned N1, unsigned N2>
75  StringSwitch& Cases(const char (&S0)[N0], const char (&S1)[N1],
76                      const char (&S2)[N2], const T& Value) {
77    return Case(S0, Value).Case(S1, Value).Case(S2, Value);
78  }
79
80  template<unsigned N0, unsigned N1, unsigned N2, unsigned N3>
81  StringSwitch& Cases(const char (&S0)[N0], const char (&S1)[N1],
82                      const char (&S2)[N2], const char (&S3)[N3],
83                      const T& Value) {
84    return Case(S0, Value).Case(S1, Value).Case(S2, Value).Case(S3, Value);
85  }
86
87  template<unsigned N0, unsigned N1, unsigned N2, unsigned N3, unsigned N4>
88  StringSwitch& Cases(const char (&S0)[N0], const char (&S1)[N1],
89                      const char (&S2)[N2], const char (&S3)[N3],
90                      const char (&S4)[N4], const T& Value) {
91    return Case(S0, Value).Case(S1, Value).Case(S2, Value).Case(S3, Value)
92      .Case(S4, Value);
93  }
94
95  T Default(const T& Value) {
96    if (ResultKnown)
97      return Result;
98
99    return Value;
100  }
101
102  operator T() {
103    assert(ResultKnown && "Fell off the end of a string-switch");
104    return Result;
105  }
106};
107
108} // end namespace llvm
109
110#endif // LLVM_ADT_STRINGSWITCH_H
111