Question

I am using the FluentValidation framework in C# which has the following two method overloads:

IRuleBuilder<TObject, TProperty>
    IRuleBuilderOptions<TObject, TProperty> Equal(TProperty toCompare, [IEqualityComparer comparer = null])
    IRuleBuilderOptions<TObject, TProperty> Equal(Expression<Func<TObject,TProperty>> expression, [IEqualityComparer comparer = null])

Basically one of the overloads lets you pass in an actual TProperty to compare, and the other lets you do a lambda that returns a TProperty from a TObject.

When I do the following it works:

RuleFor(r => r.First).Equals(r => r.Second);

It is getting the right overload in this case. When I try and pass in a value for the comparer it defaults to the other overload:

RuleFor(r => r.First).Equals(r => r.Second, new ObjectComparer()); // will not compile

This will not compile because it thinks I’m trying to use the first overload.

Is there a way I can force C# to use the second overload?

Edit:

ObjectComparer is an IEqualityComparer:

public class ObjectComparer : IEqualityComparer<MyClass>
{
     // ...
}

Answer 1

IEqualityComparer<T> does not inherit IEqualityComparer and therefore your class does not implement IEqualityComparer! Implement both of them.