Pass a lambda expression in place of IComparer or IEqualityComparer or any single-method interface?

Question

I happened to have seen some code where this guy passed a lambda expression to a ArrayList.Sort(IComparer here) or a IEnumerable.SequenceEqual(IEnumerable list, IEqualityCom

Answer 1

public class Comparer2 : IComparer, IEqualityComparer
{
    private readonly Expression> _KeyExpr;
    private readonly Func _CompiledFunc
    // Constructor
    public Comparer2(Expression> getKey)
    {
        _KeyExpr = getKey;
        _CompiledFunc = _KeyExpr.Compile();
    } 

    public int Compare(T obj1, T obj2)
    {
        return Comparer.Default.Compare(_CompiledFunc(obj1), _CompiledFunc(obj2));
    }

    public bool Equals(T obj1, T obj2)
    { 
        return EqualityComparer.Default.Equals(_CompiledFunc(obj1), _CompiledFunc(obj2));
    }

    public int GetHashCode(T obj)
    {
         return EqualityComparer.Default.GetHashCode(_CompiledFunc(obj));
    }
}

use it like this

ArrayList.Sort(new Comparer2(p => p.Name));