IEqualityComparer<T>
.The
IEqualityComparer<T>
interface implements two methods: bool Equals(T x, T y)
and int GetHashCode(T obj)
. These methods are both used by LINQ to compare objects in collections.Since i need to compare most of the business objects in my solutions, and don't want to go through the hassle of implementing tens of new classes (one per object) I wanted a generic solution.
Simple enough, I built myself the
GenericComparer<T>
.
public class GenericComparer<T> : IEqualityComparer<T>
{
public GenericComparer(Func<T, T, bool> equals, Func<T, int> getHashCode)
{
this.equals = equals;
this.getHashCode = getHashCode;
}
readonly Func<T, T, bool> equals;
public bool Equals(T x, T y)
{
return equals(x, y);
}
readonly Func<T, int> getHashCode;
public int GetHashCode(T obj)
{
return getHashCode(obj);
}
}
This worked fine. I could finally just set my comparer directly in my LINQ command. All i had to give was the expression to be used in the Equals and GetHashCode methods.
IEnumerable<mytype> result = collection.Distinct(new GenericComparer<mytype>(((mt1, mt2) => mt1.id == mt2.id), (mt => mt.id.GetHashCode())));
Still, it was more code than I would like to see. Since all I want is to receive all unique elements based on a single expression then that's all i should have to write. A simple tweak to the GenericComparer class and I got a simpler comparer
SimpleGenericComparer<T>
.
public class SimpleGenericComparer<T> : IEqualityComparer<T>
{
public SimpleGenericComparer(Func<T, int> getHashCode)
{
this.getHashCode = getHashCode;
}
public bool Equals(T x, T y)
{
return getHashCode(x) == getHashCode(y);
}
readonly Func<T, int> getHashCode;
public int GetHashCode(T obj)
{
return getHashCode(obj);
}
}
Having the Equals method simply compare both objects with the GetHashCode expression i could finaly just give the expression with which the comparison will be made.
IEnumerable<mytype> result = collection.Distinct(new SimpleGenericComparer<mytype>(mt => mt.id.GetHashCode());