Wrap a delegate in an IEqualityComparer
.net, delegates, linq
Solution
Ordinarily, I'd get this resolved by commenting @Sam on the answer (I've done some editing on the original post to clean it up a bit without altering the behavior.)
The following is my riff of @Sam's answer, with a [IMNSHO] critical fix to the default hashing policy:-
class FuncEqualityComparer<T> : IEqualityComparer<T>
{
readonly Func<T, T, bool> _comparer;
readonly Func<T, int> _hash;
public FuncEqualityComparer( Func<T, T, bool> comparer )
: this( comparer, t => 0 ) // NB Cannot assume anything about how e.g., t.GetHashCode() interacts with the comparer's behavior
{
}
public FuncEqualityComparer( Func<T, T, bool> comparer, Func<T, int> hash )
{
_comparer = comparer;
_hash = hash;
}
public bool Equals( T x, T y )
{
return _comparer( x, y );
}
public int GetHashCode( T obj )
{
return _hash( obj );
}
}
Problem
Several Linq.Enumerable functions take an `IEqualityComparer<T>`. Is there a convenient wrapper class that adapts a `delegate(T,T)=>bool` to implement `IEqualityComparer<T>`? It's easy enough to write one (if your ignore problems with defining a correct hashcode), but I'd like to know if there is an out-of-the-box solution. Specifically, I want to do set operations on `Dictionary`s, using only the Keys to define membership (while retaining the values according to different rules).