tools/gn/unique_vector.h

   1 // Copyright 2014 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #ifndef TOOLS_GN_UNIQUE_VECTOR_H_
   6 #define TOOLS_GN_UNIQUE_VECTOR_H_
   7
   8 #include <algorithm>
   9
  10 #include "base/containers/hash_tables.h"
  11
  12 namespace internal {
  13
  14 // This lass allows us to insert things by reference into a hash table which
  15 // avoids copies. The hash function of a UniquifyRef is that of the object it
  16 // points to.
  17 //
  18 // There are two ways it can store data: (1) by (vector*, index) which is used
  19 // to refer to the array in UniqueVector and make it work even when the
  20 // underlying vector is reallocated; (2) by T* which is used to do lookups
  21 // into the hash table of things that aren't in a vector yet.
  22 //
  23 // It also caches the hash value which allows us to query and then insert
  24 // without recomputing the hash.
  25 template<typename T>
  26 class UniquifyRef {
  27  public:
  28   UniquifyRef()
  29       : value_(nullptr),
  30         vect_(nullptr),
  31         index_(static_cast<size_t>(-1)),
  32         hash_val_(0) {
  33   }
  34
  35   // Initialize with a pointer to a value.
  36   explicit UniquifyRef(const T* v)
  37       : value_(v),
  38         vect_(nullptr),
  39         index_(static_cast<size_t>(-1)) {
  40     FillHashValue();
  41   }
  42
  43   // Initialize with an array + index.
  44   UniquifyRef(const std::vector<T>* v, size_t i)
  45       : value_(nullptr),
  46         vect_(v),
  47         index_(i) {
  48     FillHashValue();
  49   }
  50
  51   // Initialize with an array + index and a known hash value to prevent
  52   // re-hashing.
  53   UniquifyRef(const std::vector<T>* v, size_t i, size_t hash_value)
  54       : value_(nullptr),
  55         vect_(v),
  56         index_(i),
  57         hash_val_(hash_value) {
  58   }
  59
  60   const T& value() const { return value_ ? *value_ : (*vect_)[index_]; }
  61   size_t hash_val() const { return hash_val_; }
  62   size_t index() const { return index_; }
  63
  64  private:
  65   void FillHashValue() {
  66     BASE_HASH_NAMESPACE::hash<T> h;
  67     hash_val_ = h(value());
  68   }
  69
  70   // When non-null, points to the object.
  71   const T* value_;
  72
  73   // When value is null these are used.
  74   const std::vector<T>* vect_;
  75   size_t index_;
  76
  77   size_t hash_val_;
  78 };
  79
  80 template<typename T> inline bool operator==(const UniquifyRef<T>& a,
  81                                             const UniquifyRef<T>& b) {
  82   return a.value() == b.value();
  83 }
  84
  85 template<typename T> inline bool operator<(const UniquifyRef<T>& a,
  86                                            const UniquifyRef<T>& b) {
  87   return a.value() < b.value();
  88 }
  89
  90 }  // namespace internal
  91
  92 namespace BASE_HASH_NAMESPACE {
  93
  94 template<typename T> struct hash< internal::UniquifyRef<T> > {
  95   std::size_t operator()(const internal::UniquifyRef<T>& v) const {
  96     return v.hash_val();
  97   }
  98 };
  99
 100 }  // namespace BASE_HASH_NAMESPACE
 101
 102 // An ordered set optimized for GN's usage. Such sets are used to store lists
 103 // of configs and libraries, and are appended to but not randomly inserted
 104 // into.
 105 template<typename T>
 106 class UniqueVector {
 107  public:
 108   typedef std::vector<T> Vector;
 109   typedef typename Vector::iterator iterator;
 110   typedef typename Vector::const_iterator const_iterator;
 111
 112   const Vector& vector() const { return vector_; }
 113   size_t size() const { return vector_.size(); }
 114   bool empty() const { return vector_.empty(); }
 115   void clear() { vector_.clear(); set_.clear(); }
 116   void reserve(size_t s) { vector_.reserve(s); }
 117
 118   const T& operator[](size_t index) const { return vector_[index]; }
 119
 120   const_iterator begin() const { return vector_.begin(); }
 121   iterator begin() { return vector_.begin(); }
 122   const_iterator end() const { return vector_.end(); }
 123   iterator end() { return vector_.end(); }
 124
 125   // Returns true if the item was appended, false if it already existed (and
 126   // thus the vector was not modified).
 127   bool push_back(const T& t) {
 128     Ref ref(&t);
 129     if (set_.find(ref) != set_.end())
 130       return false;  // Already have this one.
 131
 132     vector_.push_back(t);
 133     set_.insert(Ref(&vector_, vector_.size() - 1, ref.hash_val()));
 134     return true;
 135   }
 136
 137   // Like push_back but swaps in the type to avoid a copy.
 138   bool PushBackViaSwap(T* t) {
 139     using std::swap;
 140
 141     Ref ref(t);
 142     if (set_.find(ref) != set_.end())
 143       return false;  // Already have this one.
 144
 145     size_t new_index = vector_.size();
 146     vector_.resize(new_index + 1);
 147     swap(vector_[new_index], *t);
 148     set_.insert(Ref(&vector_, vector_.size() - 1, ref.hash_val()));
 149     return true;
 150   }
 151
 152   // Appends a range of items from an iterator.
 153   template<typename iter> void Append(const iter& begin, const iter& end) {
 154     for (iter i = begin; i != end; ++i)
 155       push_back(*i);
 156   }
 157
 158   // Returns the index of the item matching the given value in the list, or
 159   // (size_t)(-1) if it's not found.
 160   size_t IndexOf(const T& t) const {
 161     Ref ref(&t);
 162     typename HashSet::const_iterator found = set_.find(ref);
 163     if (found == set_.end())
 164       return static_cast<size_t>(-1);
 165     return found->index();
 166   }
 167
 168  private:
 169   typedef internal::UniquifyRef<T> Ref;
 170   typedef base::hash_set<Ref> HashSet;
 171
 172   HashSet set_;
 173   Vector vector_;
 174 };
 175
 176 #endif  // TOOLS_GN_UNIQUE_VECTOR_H_