Find an item inside a List<T> by providing a sample object instance

Question

Why is there a List<T>.Contains(T) method but no List<T>.Find(T) method? Only the Finds that support predicates are supported. If we have an existing instance of T populated with a property value for its ID (but missing other properties) why can't we search by providing this object instance to the search in List, especially when we have implemented custom IEquatable<T> for T and would like to use what's there. But as it is, we can't, we have to repeat everything that we did in IEquatable implementation in our Find(predicate) call.

Answer 1

You can call the IEquatable<T> member(s) in your Predicate<T>. Then you won't be repeating yourself.

MyClass a = new MyClass(); //sample for finding; IEquatable<MyClass>
List<MyClass> list = GetInstances();

MyClass found = list.Find( mc => mc.Equals(a) );

Answer 2

how about this

list.Any(i => i.ID == searchObj.ID);

Answer 3

EDIT:

I think I understood your question now. You can use the List<T>.IndexOf method for this purpose:

int index = myList.IndexOf(mySample);

if(index != -1)
{
   var item = myList[index];
   // Do something with item.
}

But this would be quite strange, because clearly, your equality definition isn't quite the whole picture - it's a bit of an abuse of equality, IMO.