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The Equals() method seems needed.
The .NET documentation for GetHashCode() specifies that it should return the same value for two objects only if the objects are equal according to Equals(). For this reason, if the GetHashCode() method is redefined, the Equals method should also be redefined in order to avoid possible inconsistencies.
Redefinitions of the Equals()/GetHashCode() methods from System.Object must be consistent in the sense that, for instance, if two objects are Equals() then GetHashCode() must yield the same value on both. The validity of such a property is in general undecidable, but most incorrect definitions amount to simple cases, where one of the two methods is missing. However, it is often correct to redefine only one of those methods and the analyzer is aware of many such situations.
Inconsistent definitions of Equals()/GetHashCode() induce unexpected behaviors when objects are put inside most collection classes of the standard .NET library.
| Class Name | Defines hashCode but not equals (C#) | |||
|---|---|---|---|---|
| Significance | reliability | |||
| Mnemonic | CSHARP.IDEF.HCNOEQUALS | |||
| Categories |
|
|||
| Availability | Available for C# only. |
|||
| Enabling | Checks for this warning class are enabled by
default. To disable them, add the following WARNING_FILTER rule to the
project configuration file.
WARNING_FILTER += discard class="Defines hashCode but not equals (C#)" |
Japanese (ja)
public class MyClass
{
static void Main(string[] args)
{
MyClass p1 = new MyClass("hello");
MyClass p2 = new MyClass("hello");
Console.WriteLine("Are hashcode of p1 and hashcode of p2 the same? "+ (p1.GetHashCode() == p2.GetHashCode()));
Console.WriteLine("Are p1 and p2 equal? "+ p1.Equals(p2));
}
public string c;
public MyClass(string c)
{
this.c = c;
}
public override int GetHashCode() // "Defines hashCode but not equals (C#)" warning issued here
{
return c.GetHashCode();
}
}
The programmer should rewrite the code as follow:
public class MyClass
{
static void Main(string[] args)
{
MyClass p1 = new MyClass("hello");
MyClass p2 = new MyClass("hello");
Console.WriteLine("Are hashcode of p1 and hashcode of p2 the same? "+ (p1.GetHashCode() == p2.GetHashCode()));
Console.WriteLine("Are p1 and p2 equal? "+ p1.Equals(p2));
}
public string c;
public MyClass(string c)
{
this.c = c;
}
public override int GetHashCode()
{
return c.GetHashCode();
}
public override boolean Equals(Object other)
{
MyClass other = obj as MyClass;
if (other == null)
return false;
else
return c.Equals(other.c);
}
}
Make Equals() consistent with GetHashCode(). In many cases, this just amounts to provide the missing definition for one of them.
The following configuration file parameters affect checks for this warning class.
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