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字典

namespace System.Collections
{
    // 无序的键值对集合，key可为任意非空对象，value可为任意对象
    public interface IDictionary : ICollection
    {
        // 提供读写字典元素的方法
        object? this[object key] { get; set; }

        // 字典的key集合
        ICollection Keys { get; }

        // 字典的value集合
        ICollection Values { get; }

        // 是否包含指定key
        bool Contains(object key);

        // 添加键值对
        void Add(object key, object? value);

        // 移除所有键值对
        void Clear();

        // 是否只读
        bool IsReadOnly { get; }

        // 是否固定大小
        bool IsFixedSize { get; }
 
        // 返回 IDictionaryEnumerator 枚举器
        new IDictionaryEnumerator GetEnumerator();

        // 移除指定key的元素
        void Remove(object key);
    }
}

对应的泛型接口：

// \runtime\src\libraries\System.Private.CoreLib\src\System\Collections\Generic\IDictionary.cs
namespace System.Collections.Generic
{
    public interface IDictionary<TKey, TValue> : ICollection<KeyValuePair<TKey, TValue>>
    {
        TValue this[TKey key] { get; set; }

        ICollection<TKey> Keys { get; }

        ICollection<TValue> Values { get; }

        bool ContainsKey(TKey key);

        void Add(TKey key, TValue value);

        bool Remove(TKey key);

        bool TryGetValue(TKey key, [MaybeNullWhen(false)] out TValue value);
    }
}

字典中的键值对：

// \runtime\src\libraries\System.Private.CoreLib\src\System\Collections\Generic\DictionaryEntry.cs
namespace System.Collections
{
    // 字典的key-value 对
    // 由 IDictionaryEnumerator::GetEntry() 返回
    public struct DictionaryEntry
    {
        private object _key;
        private object? _value;

        public DictionaryEntry(object key, object? value) { _key = key; _value = value; }

        public object Key { get => _key; set => _key = value; }

        public object? Value { get => _value; set => _value = value; }

        public void Deconstruct(out object key, out object? value) { key = Key; value = Value; }

        public override string ToString() => KeyValuePair.PairToString(_key, _value);
    }
}