js/src/gc/IteratorUtils.h

   1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
   2  * vim: set ts=8 sts=2 et sw=2 tw=80:
   3  * This Source Code Form is subject to the terms of the Mozilla Public
   4  * License, v. 2.0. If a copy of the MPL was not distributed with this
   5  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   6
   7 #ifndef gc_IteratorUtils_h
   8 #define gc_IteratorUtils_h
   9
  10 #include "mozilla/Array.h"
  11 #include "mozilla/Maybe.h"
  12
  13 #include <initializer_list>
  14
  15 namespace js {
  16
  17 /*
  18  * Create an iterator that yields the values from IteratorB(a) for all a in
  19  * IteratorA(). Equivalent to nested for loops over IteratorA and IteratorB
  20  * where IteratorB is constructed with a value from IteratorA.
  21  */
  22 template <typename IteratorA, typename IteratorB>
  23 class NestedIterator {
  24   using T = decltype(std::declval<IteratorB>().get());
  25
  26   IteratorA a;
  27   mozilla::Maybe<IteratorB> b;
  28
  29  public:
  30   template <typename... Args>
  31   explicit NestedIterator(Args&&... args) : a(std::forward<Args>(args)...) {
  32     settle();
  33   }
  34
  35   bool done() const { return b.isNothing(); }
  36
  37   T get() const {
  38     MOZ_ASSERT(!done());
  39     return b.ref().get();
  40   }
  41
  42   void next() {
  43     MOZ_ASSERT(!done());
  44     b->next();
  45     if (b->done()) {
  46       b.reset();
  47       a.next();
  48       settle();
  49     }
  50   }
  51
  52   const IteratorB& ref() const { return *b; }
  53
  54   operator T() const { return get(); }
  55
  56   T operator->() const { return get(); }
  57
  58  private:
  59   void settle() {
  60     MOZ_ASSERT(b.isNothing());
  61     while (!a.done()) {
  62       b.emplace(a.get());
  63       if (!b->done()) {
  64         break;
  65       }
  66       b.reset();
  67       a.next();
  68     }
  69   }
  70 };
  71
  72 /*
  73  * An iterator the yields values from each of N of instances of Iterator in
  74  * sequence.
  75  */
  76 template <typename Iterator, size_t N>
  77 class ChainedIterator {
  78   using T = decltype(std::declval<Iterator>().get());
  79
  80   mozilla::Array<Iterator, N> iterators;
  81   size_t index = 0;
  82
  83  public:
  84   template <typename... Args>
  85   MOZ_IMPLICIT ChainedIterator(Args&&... args)
  86       : iterators(Iterator(std::forward<Args>(args))...) {
  87     static_assert(N > 1);
  88     settle();
  89   }
  90
  91   bool done() const { return index == N; }
  92
  93   void next() {
  94     MOZ_ASSERT(!done());
  95     iterators[index].next();
  96     settle();
  97   }
  98
  99   T get() const {
 100     MOZ_ASSERT(!done());
 101     return iterators[index].get();
 102   }
 103
 104   operator T() const { return get(); }
 105   T operator->() const { return get(); }
 106
 107  private:
 108   void settle() {
 109     MOZ_ASSERT(!done());
 110     while (iterators[index].done()) {
 111       index++;
 112       if (done()) {
 113         break;
 114       }
 115     }
 116   }
 117 };
 118
 119 } /* namespace js */
 120
 121 #endif  // gc_IteratorUtils_h