Question

If you use ‘RemoveAll’ inside a generic class that you intend to be used to hold a collection of any type object, like this:

public class SomeClass<T>
{
     internal List<T> InternalList;

     public SomeClass() { InternalList = new List<T>(); }

     public void RemoveAll(T theValue)
     {
       //  this will work
       InternalList.RemoveAll(x => x.Equals(theValue));

       // the usual form of Lambda Predicate 
       // for RemoveAll will not compile
       // error: Cannot apply operator '==' to operands of Type 'T' and 'T'
       // InternalList.RemoveAll(x => x == theValue);
     }
}

Answer 1

If you want to make the code as flexible as possible, you can use EqualityComparer<T>.Default like this:

public void RemoveAll(T theValue)
{
    //  this will work
    InternalList.RemoveAll(x => EqualityComparer<T>.Default.Equals(x, theValue));
}

That code will work for any type of T (including nullable types and value types), it avoids boxing and it will also handle cases where T implements IEquatable<T> or overrides object.Equals. From the documentation:

The Default property checks whether type T implements the
System.IEquatable(T) interface and, if so, returns an
EqualityComparer(T) that uses that implementation. Otherwise, it
returns an EqualityComparer(T) that uses the overrides of
Object.Equals and Object.GetHashCode provided by T.