ObjectIDGenerator与哈希集<T>

ObjectIdGenerator查看引用标识。当检查一个对象是否已经存在时,它只会对两个对象实例执行==调用。这将归结为引用比较,因为此时对象是静态类型的对象。这很好,除非你的对象明确使用。Equals()表示相等。如果两个对象相等。等于()但引用不同,ObjectIDGenerator会将它们视为不同的对象。可能不是你想要的。

显示差异的示例代码:

class Person
{
    public readonly string Name;
    public Person(string name) { Name = name; }
    public override int GetHashCode()
    {
        return Name.GetHashCode();
    }
    public override bool Equals(object obj)
    {
        var other = obj as Person;
        if (other == null)
        {
            return false;
        }
        return StringComparer.Ordinal.Equals(Name, other.Name);
    }
}

public static void Example()
{
    var gen = new ObjectIDGenerator();
    bool isFirst;
    var person1 = new Person("John");
    var person2 = new Person("Bob");
    gen.GetId(person1, out isFirst);    // isFirst = true
    gen.GetId(person1, out isFirst);    // isFirst = false
    gen.GetId(person2, out isFirst);    // isFirst = true
    gen.GetId(new Person("John"), out isFirst); // isFirst = true even though they are .Equals()

    var set = new HashSet<Person>();
    set.Add(person1);
    var contains1 = set.Contains(person1);              // true
    var contains2 = set.Contains(new Person("John"));   // true
}