[英]Is there any reason not to generate conditional hash codes using GetHashCode in .NET?
在我用作文檔或文檔+頁面標識符的類中,我使用以下GetHashCode實現。 它感覺'正確',但由於我之前沒有真正看到這種方法中特定領域的條件,我想知道是否有理由不這樣做。 當然,ToString方法也具有相同的條件。
public override int GetHashCode ()
{
int hash = 0;
unchecked
{
hash = 17;
hash = hash * 23 + this.ProductManufacturer.Value.GetHashCode();
hash = hash * 23 + this.ProductName.Value.GetHashCode();
hash = hash * 23 + this.ProductVersion.Value.GetHashCode();
hash = hash * 23 + this.Guid.Value.GetHashCode();
if (this.Type != IdentifierType.Document)
{
hash = hash * 23 + this.PageNumber.Value.GetHashCode();
hash = hash * 23 + this.PageCount.Value.GetHashCode();
}
}
return (hash);
}
根據答案和Eric的鏈接更新了代碼 :
public bool Equals (Identifier other)
{
return (this.Equals(other, this.Type));
}
public override bool Equals (object obj)
{
return ((obj is HouseOIdentifier) && (this.Equals(obj as Identifier)));
}
public bool Equals (Identifier other, IdentifierType type)
{
bool result = false;
if (object.ReferenceEquals(this, other))
{
result = true;
}
else if (!object.ReferenceEquals(other, null))
{
result
= (this.Type == other.Type)
&& (this.ProductManufacturer.Key == other.ProductManufacturer.Key)
&& (this.ProductManufacturer.Value == other.ProductManufacturer.Value)
&& (this.ProductName.Key == other.ProductName.Key)
&& (this.ProductName.Value == other.ProductName.Value)
&& (this.ProductVersion.Key == other.ProductVersion.Key)
&& (this.ProductVersion.Value == other.ProductVersion.Value)
&& (this.Guid.Key == other.Guid.Key)
&& (this.Guid.Value == other.Guid.Value)
;
if (type == IdentifierType.Page)
{
result
&= (this.PageNumber.Key == other.PageNumber.Key)
&& (this.PageNumber.Value == other.PageNumber.Value)
&& (this.PageCount.Key == other.PageCount.Key)
&& (this.PageCount.Value == other.PageCount.Value)
;
}
}
return (result);
}
public override int GetHashCode ()
{
int hash = 0;
unchecked // Overflow is fine, just wrap.
{
hash = 17;
hash = hash * 23 + this.Type.GetHashCode();
hash = hash * 23 + this.ProductManufacturer.Key.GetHashCode();
hash = hash * 23 + this.ProductManufacturer.Value.GetHashCode();
hash = hash * 23 + this.ProductName.Key.GetHashCode();
hash = hash * 23 + this.ProductName.Value.GetHashCode();
hash = hash * 23 + this.ProductVersion.Key.GetHashCode();
hash = hash * 23 + this.ProductVersion.Value.GetHashCode();
hash = hash * 23 + this.Guid.Key.GetHashCode();
hash = hash * 23 + this.Guid.Value.GetHashCode();
if (this.Type == HouseOfSynergy.FastForm.Core.Identifier.EnumType.Page)
{
hash = hash * 23 + this.PageNumber.Key.GetHashCode();
hash = hash * 23 + this.PageNumber.Value.GetHashCode();
hash = hash * 23 + this.PageCount.Key.GetHashCode();
hash = hash * 23 + this.PageCount.Value.GetHashCode();
}
}
return (hash);
}
public override string ToString ()
{
return ("whatever");
}
只要等對象具有相同的哈希碼,您的實現就可以了。 這是唯一的要求。 如何計算哈希碼,即是否使用if語句,並不重要。
(另外,如果哈希代碼在對象的生命周期中從未改變過,那將是很好的,因為它幾乎打破了使用哈希代碼的任何數據結構。最理想的是,對象應該是不可變的。)
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