StringSwitch.h revision 208954 
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//  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 <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, typename R = T>
42class StringSwitch {
43  /// \brief The string we are matching.
44  StringRef Str;
45
46  /// \brief The pointer to the result of this switch statement, once known,
47  /// null before that.
48  const T *Result;
49
50public:
51  explicit StringSwitch(StringRef Str)
52  : Str(Str), Result(0) { }
53
54  template<unsigned N>
55  StringSwitch& Case(const char (&S)[N], const T& Value) {
56    if (!Result && N-1 == Str.size() &&
57        (std::memcmp(S, Str.data(), N-1) == 0)) {
58      Result = &Value;
59    }
60
61    return *this;
62  }
63
64  template<unsigned N0, unsigned N1>
65  StringSwitch& Cases(const char (&S0)[N0], const char (&S1)[N1],
66                      const T& Value) {
67    return Case(S0, Value).Case(S1, Value);
68  }
69
70  template<unsigned N0, unsigned N1, unsigned N2>
71  StringSwitch& Cases(const char (&S0)[N0], const char (&S1)[N1],
72                      const char (&S2)[N2], const T& Value) {
73    return Case(S0, Value).Case(S1, Value).Case(S2, Value);
74  }
75
76  template<unsigned N0, unsigned N1, unsigned N2, unsigned N3>
77  StringSwitch& Cases(const char (&S0)[N0], const char (&S1)[N1],
78                      const char (&S2)[N2], const char (&S3)[N3],
79                      const T& Value) {
80    return Case(S0, Value).Case(S1, Value).Case(S2, Value).Case(S3, Value);
81  }
82
83  template<unsigned N0, unsigned N1, unsigned N2, unsigned N3, unsigned N4>
84  StringSwitch& Cases(const char (&S0)[N0], const char (&S1)[N1],
85                      const char (&S2)[N2], const char (&S3)[N3],
86                      const char (&S4)[N4], const T& Value) {
87    return Case(S0, Value).Case(S1, Value).Case(S2, Value).Case(S3, Value)
88      .Case(S4, Value);
89  }
90
91  R Default(const T& Value) const {
92    if (Result)
93      return *Result;
94
95    return Value;
96  }
97
98  operator R() const {
99    assert(Result && "Fell off the end of a string-switch");
100    return *Result;
101  }
102};
103
104} // end namespace llvm
105
106#endif // LLVM_ADT_STRINGSWITCH_H
107