libc/src/__support/fixedvector.h

   1 //===-- A data structure for a fixed capacity data store --------*- C++ -*-===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8
   9 #ifndef LLVM_LIBC_SUPPORT_FIXEDVECTOR_H
  10 #define LLVM_LIBC_SUPPORT_FIXEDVECTOR_H
  11
  12 #include "src/__support/CPP/array.h"
  13
  14 namespace __llvm_libc {
  15
  16 // A fixed size data store backed by an underlying cpp::array data structure. It
  17 // supports vector like API but is not resizable like a vector.
  18 template <typename T, size_t CAPACITY> class FixedVector {
  19   cpp::array<T, CAPACITY> store;
  20   size_t item_count = 0;
  21
  22 public:
  23   constexpr FixedVector() = default;
  24
  25   bool push_back(const T &obj) {
  26     if (item_count == CAPACITY)
  27       return false;
  28     store[item_count] = obj;
  29     ++item_count;
  30     return true;
  31   }
  32
  33   const T &back() const { return store[item_count - 1]; }
  34
  35   T &back() { return store[item_count - 1]; }
  36
  37   bool pop_back() {
  38     if (item_count == 0)
  39       return false;
  40     --item_count;
  41     return true;
  42   }
  43
  44   bool empty() const { return item_count == 0; }
  45
  46   // Empties the store for all practical purposes.
  47   void reset() { item_count = 0; }
  48
  49   // This static method does not free up the resources held by |store|,
  50   // say by calling `free` or something similar. It just does the equivalent
  51   // of the `reset` method. Considering that FixedVector is of fixed storage,
  52   // a `destroy` method like this should not be required. However, FixedVector
  53   // is used in a few places as an alternate for data structures which use
  54   // dynamically allocated storate. So, the `destroy` method like this
  55   // matches the `destroy` API of those other data structures so that users
  56   // can easily swap one data structure for the other.
  57   static void destroy(FixedVector<T, CAPACITY> *store) { store->reset(); }
  58 };
  59
  60 } // namespace __llvm_libc
  61
  62 #endif // LLVM_LIBC_SUPPORT_FIXEDVECTOR_H