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使用GetHashCode测试Equals重写中的相等性

gethashcode c#

Armbrat · 技术社区 · 15 年前

是否可以调用GetHashCode作为方法从Equals重写内部测试相等性?

例如,这个代码可以接受吗?

public class Class1
{
  public string A
  {
    get;
    set;
  }

  public string B
  {
    get;
    set;
  }

  public override bool Equals(object obj)
  {
    Class1 other = obj as Class1;
    return other != null && other.GetHashCode() == this.GetHashCode();
  }

  public override int GetHashCode()
  {
    int result = 0;
    result = (result ^ 397) ^ (A == null ? 0 : A.GetHashCode());
    result = (result ^ 397) ^ (B == null ? 0 : B.GetHashCode());
    return result;
  }
}

8 回复 | 直到 12 年前

Eric Lippert 15 年前

public static void Main()
{
    var c1 = new Class1() { A = "apahaa", B = null };
    var c2 = new Class1() { A = "abacaz", B = null };
    Console.WriteLine(c1.Equals(c2));
}

http://blogs.msdn.com/b/ericlippert/archive/2010/03/22/socks-birthdays-and-hash-collisions.aspx

ulrichb 15 年前

equality <=> hashcode equality

equality => hashcode equality

hashcode inequality => inequality

http://msdn.microsoft.com/en-us/library/system.object.gethashcode.aspx

Dan Tao 15 年前

Equals

JaredPar 15 年前

Equals true false

Jim Mischel 15 年前

GetHashCode

public override bool Equals(object obj)
  {
    Class1 other = obj as Class1;
    if (other == null || other.GetHashCode() != this.GetHashCode())
        return false;
    // the hash codes are the same so you have to do a full object compare.
  }

Gabe Timothy Khouri 15 年前

GetHashCode Equals if (this.GetHashCode() != other.GetHashCode()) return false;

Jon Hanna 15 年前

GetHashCode()

private bool IsMatch(KeyType newItem, KeyType storedItem, int newHash, int oldHash)
{
  return ReferenceEquals(newItem, storedItem) // fast, false negatives, no false positives (only applicable to reference types)
    ||
    (
      newHash == oldHash // fast, false positives, no fast negatives
      &&
      _cmp.Equals(newItem, storedItem) // slow for some types, but always correct result.
    );
}

_cmp.Equals int

nawfal Donny V. 12 年前

GetHashCode

if (other.GetHashCode() != this.GetHashCode()
    return false;

Equals

var watch = Stopwatch.StartNew();
for (int i = 0; i < 100000; i++) 
{
    action(); //Equals and GetHashCode called here to test for performance.
}
watch.Stop();
Console.WriteLine(watch.Elapsed.TotalMilliseconds);