src/mscorlib/shared/System/Collections/Generic/ValueListBuilder.cs

   1 // Licensed to the .NET Foundation under one or more agreements.
   2 // The .NET Foundation licenses this file to you under the MIT license.
   3 // See the LICENSE file in the project root for more information.
   4
   5 using System.Buffers;
   6 using System.Diagnostics;
   7 using System.Runtime.CompilerServices;
   8
   9 namespace System.Collections.Generic
  10 {
  11     internal ref partial struct ValueListBuilder<T>
  12     {
  13         private Span<T> _span;
  14         private T[] _arrayFromPool;
  15         private int _pos;
  16
  17         public ValueListBuilder(Span<T> initialSpan)
  18         {
  19             _span = initialSpan;
  20             _arrayFromPool = null;
  21             _pos = 0;
  22         }
  23
  24         public int Length => _pos;
  25
  26         public ref T this[int index]
  27         {
  28             get
  29             {
  30                 Debug.Assert(index < _pos);
  31                 return ref _span[index];
  32             }
  33         }
  34
  35         [MethodImpl(MethodImplOptions.AggressiveInlining)]
  36         public void Append(T item)
  37         {
  38             int pos = _pos;
  39             if (pos >= _span.Length)
  40                 Grow();
  41
  42             _span[pos] = item;
  43             _pos = pos + 1;
  44         }
  45
  46         public ReadOnlySpan<T> AsSpan()
  47         {
  48             return _span.Slice(0, _pos);
  49         }
  50
  51         [MethodImpl(MethodImplOptions.AggressiveInlining)]
  52         public void Dispose()
  53         {
  54             if (_arrayFromPool != null)
  55             {
  56                 ArrayPool<T>.Shared.Return(_arrayFromPool);
  57                 _arrayFromPool = null;
  58             }
  59         }
  60
  61         private void Grow()
  62         {
  63             T[] array = ArrayPool<T>.Shared.Rent(_span.Length * 2);
  64
  65             bool success = _span.TryCopyTo(array);
  66             Debug.Assert(success);
  67
  68             T[] toReturn = _arrayFromPool;
  69             _span = _arrayFromPool = array;
  70             if (toReturn != null)
  71             {
  72                 ArrayPool<T>.Shared.Return(toReturn);
  73             }
  74         }
  75     }
  76 }