C# HashSet<T>只读解决方案
C# HashSet<T>只读解决方案
提问于 2016-04-23 18:54:43
下面是这个示例代码：
static class Store
{
private static List<String> strList = new List<string>();
private static HashSet<String> strHashSet = new HashSet<string>();
public static List<String> NormalList
{
get { return strList; }
}
public static HashSet<String> NormalHashSet
{
get { return strHashSet; }
}
public static IReadOnlyList<String> ReadonlyList
{
get { return (IReadOnlyList<String>)strList; }
}
public static IReadOnlyCollection<String> ReadonlyHashSet
{
get { return (IReadOnlyCollection<String>)strHashSet; }
}
public static IReadOnlyList<String> Real_ReadonlyList
{
get { return (IReadOnlyList<String>)strList.AsReadOnly(); }
}
public static IReadOnlyCollection<String> Real_ReadonlyHashSet
{
get
{
List<String> tmpList = new List<String>(strHashSet);
return (IReadOnlyList<String>)(tmpList).AsReadOnly();
}
}
}下面是一个测试代码：
// normal behaviour
// you can modify the list and the hashset
Store.NormalList.Add("some string 1");
Store.NormalHashSet.Add("some string 1");
// tricky behaviour
// you can still modify the list and the hashset
((List<String>)Store.ReadonlyList).Add("some string 2");
((HashSet<String>)Store.ReadonlyHashSet).Add("some string 2");
// expected read-only behaviour
// you can NOT modify
// throws InvalidCastException
((List<String>)Store.Real_ReadonlyList).Add("some string 3");
// throws InvalidCastException
((HashSet<String>)Store.Real_ReadonlyHashSet).Add("some string 3");我的问题是：
"Real_ReadonlyHashSet“属性有更好的解决方案吗？
微软有一天会在HashSet上实现“HashSet”方法吗？
回答 5
Stack Overflow用户
回答已采纳
发布于 2016-04-23 19:18:15
这里是代码的全部 of .AsReadOnly()
public ReadOnlyCollection<T> AsReadOnly() {
Contract.Ensures(Contract.Result<ReadOnlyCollection<T>>() != null);
return new ReadOnlyCollection<T>(this);
}如果不使用CodeContracts，甚至没有必要使用第一行。但是，ReadOnlyCollection<T>只支持HashSet<T>不支持的IList<T>。
我要做的是创建您自己的ReadOnlySet<T>类，它接受一个ISet<T>，并且只通过读操作在内部。
更新:这里的是一个完全充实的ReadOnlySet<T>，我很快编写了一个扩展方法，将.AsReadOnly()添加到实现ISet<T>的任何东西上
public static class SetExtensionMethods
{
public static ReadOnlySet<T> AsReadOnly<T>(this ISet<T> set)
{
return new ReadOnlySet<T>(set);
}
}
public class ReadOnlySet<T> : IReadOnlyCollection<T>, ISet<T>
{
private readonly ISet<T> _set;
public ReadOnlySet(ISet<T> set)
{
_set = set;
}
public IEnumerator<T> GetEnumerator()
{
return _set.GetEnumerator();
}
IEnumerator IEnumerable.GetEnumerator()
{
return ((IEnumerable) _set).GetEnumerator();
}
void ICollection<T>.Add(T item)
{
throw new NotSupportedException("Set is a read only set.");
}
public void UnionWith(IEnumerable<T> other)
{
throw new NotSupportedException("Set is a read only set.");
}
public void IntersectWith(IEnumerable<T> other)
{
throw new NotSupportedException("Set is a read only set.");
}
public void ExceptWith(IEnumerable<T> other)
{
throw new NotSupportedException("Set is a read only set.");
}
public void SymmetricExceptWith(IEnumerable<T> other)
{
throw new NotSupportedException("Set is a read only set.");
}
public bool IsSubsetOf(IEnumerable<T> other)
{
return _set.IsSubsetOf(other);
}
public bool IsSupersetOf(IEnumerable<T> other)
{
return _set.IsSupersetOf(other);
}
public bool IsProperSupersetOf(IEnumerable<T> other)
{
return _set.IsProperSupersetOf(other);
}
public bool IsProperSubsetOf(IEnumerable<T> other)
{
return _set.IsProperSubsetOf(other);
}
public bool Overlaps(IEnumerable<T> other)
{
return _set.Overlaps(other);
}
public bool SetEquals(IEnumerable<T> other)
{
return _set.SetEquals(other);
}
public bool Add(T item)
{
throw new NotSupportedException("Set is a read only set.");
}
public void Clear()
{
throw new NotSupportedException("Set is a read only set.");
}
public bool Contains(T item)
{
return _set.Contains(item);
}
public void CopyTo(T[] array, int arrayIndex)
{
_set.CopyTo(array, arrayIndex);
}
public bool Remove(T item)
{
throw new NotSupportedException("Set is a read only set.");
}
public int Count
{
get { return _set.Count; }
}
public bool IsReadOnly
{
get { return true; }
}
}Stack Overflow用户
发布于 2022-06-03 06:36:54
从.NET 5开始，HashSet类现在实现了IReadOnlySet接口。但是没有内置的ReadOnlySet<T>包装器，类似于字典的现有ReadOnlyDictionary类，但是实现一个非常简单：
public class ReadOnlySet<T> : IReadOnlySet<T>
{
private readonly ISet<T> _set;
public ReadOnlySet(ISet<T> set) { ArgumentNullException.ThrowIfNull(set); _set = set; }
public int Count => _set.Count;
public bool Contains(T item) => _set.Contains(item);
public bool IsProperSubsetOf(IEnumerable<T> other) => _set.IsProperSubsetOf(other);
public bool IsProperSupersetOf(IEnumerable<T> other) => _set.IsProperSupersetOf(other);
public bool IsSubsetOf(IEnumerable<T> other) => _set.IsSubsetOf(other);
public bool IsSupersetOf(IEnumerable<T> other) => _set.IsSupersetOf(other);
public bool Overlaps(IEnumerable<T> other) => _set.Overlaps(other);
public bool SetEquals(IEnumerable<T> other) => _set.SetEquals(other);
public IEnumerator<T> GetEnumerator() => _set.GetEnumerator();
IEnumerator IEnumerable.GetEnumerator() => GetEnumerator();
}即将发布的.NET 7还将为IDictionary<TKey,TValue>提供一个新的AsReadOnly扩展方法，因此我们也为ISet<T>提供一个扩展方法：
public static ReadOnlySet<T> AsReadOnly<T>(this ISet<T> set) => new ReadOnlySet<T>(set);用法示例：
HashSet<Item> items = new();
ReadOnlySet<Item> readOnlyItems = items.AsReadOnly();Stack Overflow用户
发布于 2016-04-23 19:25:00
您可以编写自己的IReadOnlyCollection<T>实现，它包装了一个IEnumerable<T>和一个计数：
public sealed class ReadOnlyCollectionFromEnumerable<T>: IReadOnlyCollection<T>
{
readonly IEnumerable<T> _data;
public ReadOnlyCollectionFromEnumerable(IEnumerable<T> data, int count)
{
_data = data;
Count = count;
}
public IEnumerator<T> GetEnumerator()
{
return _data.GetEnumerator();
}
IEnumerator IEnumerable.GetEnumerator()
{
return GetEnumerator();
}
public int Count { get; }
}然后像这样声明您的ReadonlyHashSet属性：
public static IReadOnlyCollection<String> ReadonlyHashSet
{
get { return new ReadOnlyCollectionFromEnumerable<string>(strHashSet, strHashSet.Count); }
}我认为这样可以解决这个问题。
页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/36815062
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