src/base/LookupTable.h

   1 /*
   2  * Copyright (C) 1996-2018 The Squid Software Foundation and contributors
   3  *
   4  * Squid software is distributed under GPLv2+ license and includes
   5  * contributions from numerous individuals and organizations.
   6  * Please see the COPYING and CONTRIBUTORS files for details.
   7  */
   8
   9 #ifndef SQUID_LOOKUPTABLE_H_
  10 #define SQUID_LOOKUPTABLE_H_
  11
  12 #include "sbuf/Algorithms.h"
  13 #include "sbuf/SBuf.h"
  14
  15 #include <unordered_map>
  16
  17 /**
  18  * a record in the initializer list for a LookupTable
  19  *
  20  * In case it is wished to extend the structure of a LookupTable's initializer
  21  * list, it can be done by using a custom struct which must match
  22  * LookupTableRecord's signature plus any extra custom fields the user may
  23  * wish to add; the extended record type must then be passed as RecordType
  24  * template parameter to LookupTable.
  25  */
  26 template <typename EnumType>
  27 struct LookupTableRecord
  28 {
  29     const char *name;
  30     EnumType id;
  31 };
  32
  33 /**
  34  * SBuf -> case-insensitive enum lookup table
  35  *
  36  * How to use:
  37  * enum enum_type { ... };
  38  * static const LookupTable<enum_type>::Record initializerTable[] = {
  39  *   {"key1", ENUM_1}, {"key2", ENUM_2}, ... {nullptr, ENUM_INVALID_VALUE}
  40  * };
  41  * LookupTable<enum_type> lookupTableInstance(ENUM_INVALID_VALUE, initializerTable);
  42  *
  43  * then in the code:
  44  * SBuf s(string_to_lookup);
  45  * enum_type item = lookupTableInstance.lookup(s);
  46  * if (item != ENUM_INVALID_VALUE) { // do stuff }
  47  *
  48  */
  49
  50 class SBufCaseInsensitiveLess : public std::binary_function<SBuf, SBuf, bool> {
  51 public:
  52     bool operator() (const SBuf &x, const SBuf &y) const {
  53         return x.caseCmp(y) < 0;
  54     }
  55 };
  56
  57 template<typename EnumType, typename RecordType = LookupTableRecord<EnumType>, typename Hasher = CaseInsensitiveSBufHash >
  58 class LookupTable
  59 {
  60 public:
  61     /// element of the lookup table initialization list
  62     typedef RecordType Record;
  63
  64     LookupTable(const EnumType theInvalid, const Record data[]) :
  65         invalidValue(theInvalid)
  66     {
  67         for (auto i = 0; data[i].name != nullptr; ++i) {
  68             lookupTable[SBuf(data[i].name)] = data[i].id;
  69         }
  70     }
  71
  72     EnumType lookup(const SBuf &key) const {
  73         auto r = lookupTable.find(key);
  74         if (r == lookupTable.end())
  75             return invalidValue;
  76         return r->second;
  77     }
  78
  79 private:
  80     typedef std::unordered_map<const SBuf, EnumType, Hasher> lookupTable_t;
  81     lookupTable_t lookupTable;
  82     EnumType invalidValue;
  83 };
  84
  85 #endif /* SQUID_LOOKUPTABLE_H_ */
  86