49 lines
1.4 KiB
C#
49 lines
1.4 KiB
C#
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using System.Collections;
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namespace OECS;
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/// <summary>
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/// An insertion-ordered set of entities that supports O(1) Add, Remove, and Contains
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/// while iterating in insertion order. Drop-in for cases where both
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/// stable ordering and fast membership checks are needed.
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///
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/// Not thread-safe.
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/// </summary>
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internal sealed class OrderedEntitySet : IReadOnlyCollection<Entity>
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{
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// Entities are stored in a packed list; a secondary dictionary maps
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// each entity to its index for O(1) removal via swap-with-last.
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private readonly List<Entity> _order = new();
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private readonly Dictionary<Entity, int> _index = new();
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public int Count => _order.Count;
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public bool Add(Entity entity)
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{
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if (_index.ContainsKey(entity))
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return false;
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_index[entity] = _order.Count;
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_order.Add(entity);
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return true;
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}
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public bool Remove(Entity entity)
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{
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if (!_index.Remove(entity, out var idx))
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return false;
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int lastIdx = _order.Count - 1;
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if (idx < lastIdx)
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{
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var last = _order[lastIdx];
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_order[idx] = last;
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_index[last] = idx;
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}
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_order.RemoveAt(lastIdx);
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return true;
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}
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public IEnumerator<Entity> GetEnumerator() => _order.GetEnumerator();
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IEnumerator IEnumerable.GetEnumerator() => GetEnumerator();
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}
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