空列表或字典的内存使用情况？

Question

空列表或字典使用了多少内存？如:

List<double> list = new List<double>();

指针本身在x86和64位x64操作系统上至少占用32位,但是列表本身呢？有0条记录.

问的原因是,你可以通过设置列表来节省一些字节null吗？

(想象一下,你有一个类,其中包含一些List<T>在某些情况下正在使用的类,在其他情况下它不是,在这种情况下有一个boolean喜欢IsEmpty而null不是空列表可能会节省一些操作内存.特别是如果你有成千上万的这样的操作内存中的类,每一位都很重要.)

Answer 1

由dotPeek反编译:

public class List<T> : IList<T>, ICollection<T>, IList, ICollection, IReadOnlyList<T>, IReadOnlyCollection<T>, IEnumerable<T>, IEnumerable
{
    private T[] _items; //4 bytes for x86, 8 for x64
    private int _size; //4 bytes
    private int _version; //4 bytes
    [NonSerialized]
    private object _syncRoot; //4 bytes for x86, 8 for x64
    private static readonly T[] _emptyArray; //one per type
    private const int _defaultCapacity = 4; //one per type
    ...
}

你在x86上总共有20个字节(16个用于List<T>成员,4个用于元数据参考开销)和32个用于x64,包括对对象类型的响应,.net中的每个对象都有.这种计算大致不包括计数.

public class Dictionary<TKey, TValue> : ...
{
    private int[] buckets; //4 bytes for x86, 8 for x64
    private Dictionary<TKey, TValue>.Entry[] entries; //4 bytes for x86, 8 for x64
    private int count; //4 bytes
    private int version; //4 bytes
    private int freeList; //4 bytes
    private int freeCount; //4 bytes
    private IEqualityComparer<TKey> comparer; //4 bytes for x86, 8 for x64
    private Dictionary<TKey, TValue>.KeyCollection keys; //4 bytes for x86, 8 for x64
    private Dictionary<TKey, TValue>.ValueCollection values; //4 bytes for x86, 8 for x64
    private object _syncRoot; //4 bytes for x86, 8 for x64

    private const string VersionName = "Version"; //one per type
    private const string HashSizeName = "HashSize"; //one per type
    private const string KeyValuePairsName = "KeyValuePairs"; //one per type
    private const string ComparerName = "Comparer"; //one per type
}

x86 为44,x64 为72.再次粗略计算,因为需要不同对象的实例.