src/base/LookupTable.h

   1 /*
   2  * Copyright (C) 1996-2020 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 template<typename EnumType, typename RecordType = LookupTableRecord<EnumType>, typename Hasher = CaseInsensitiveSBufHash >
  51 class LookupTable
  52 {
  53 public:
  54     /// element of the lookup table initialization list
  55     typedef RecordType Record;
  56
  57     LookupTable(const EnumType theInvalid, const Record data[]) :
  58         invalidValue(theInvalid)
  59     {
  60         for (auto i = 0; data[i].name != nullptr; ++i) {
  61             lookupTable[SBuf(data[i].name)] = data[i].id;
  62         }
  63     }
  64
  65     EnumType lookup(const SBuf &key) const {
  66         auto r = lookupTable.find(key);
  67         if (r == lookupTable.end())
  68             return invalidValue;
  69         return r->second;
  70     }
  71
  72 private:
  73     typedef std::unordered_map<const SBuf, EnumType, Hasher> lookupTable_t;
  74     lookupTable_t lookupTable;
  75     EnumType invalidValue;
  76 };
  77
  78 #endif /* SQUID_LOOKUPTABLE_H_ */
  79