Hi
In the documentation is stated that the default constructor of
Dictionary<TKey, TValue> will use EqualityComparer.Default, that will use
the IEquatable interface if TKey implements it. That is not the case. If we
set a breakpoint in the IEquatable<TKey>.Equals, it isn't called, and the
Dictionary class seems to be basing its results on GetHashCode of TKey
instances. This program:
public class A : IEquatable<A>
{
private int _i;
public A(int i) { _i = i; }
bool IEquatable<A>.Equals(A other) { return _i.Equals(other._i); }
public static void Main()
{
if (!EqualityComparer<A>.Default.Equals(new A(2), new A(2)))
Console.WriteLine("BUG 1");
Dictionary<A, int> d = new Dictionary<A, int>();
A a = new A(2);
d.Add(a, 3);
int value;
if (!d.TryGetValue(new A(2), out value))
Console.WriteLine("BUG 2");
if (!d.TryGetValue(a, out value))
Console.WriteLine("BUG 3");
d = new Dictionary<A, int>(new EqualityComparer<A>.Default);
d.Add(a, 3);
if (!d.TryGetValue(new A(2), out value))
Console.WriteLine("BUG 4");
}
}
Will print:
BUG2
BUG4
When it shouldn't print anything.
The problem seems to be not in EqualityComparer<>.Default but in Dictionary
that doesn't use it.
Best regards,
Gustavo Guerra
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