C# Difference between First() and Find()

Question

So I know that Find() is only a List<T> method, whereas First() is an extension for any IEnumerable<T>. I also know that First() will return the first element if no parameter is passed, whereas Find() will throw an exception. Lastly, I know that First() will throw an exception if the element is not found, whereas Find() will return the type's default value.

I hope that clears up confusion about what I'm actually asking. This is a computer science question and deals with these methods at the computational level. I've come to understand that IEnumerable<T> extensions do not always operate as one would expect under the hood. So here's the Q, and I mean from a "close to the metal" standpoint: What is the difference between Find() and First()?

Here's some code to provide basic assumptions to operate under for this question.

var l = new List<int> { 1, 2, 3, 4, 5 }; var x = l.First(i => i == 3); var y = l.Find(i => i == 3); 

Is there any actual computational difference between how First() and Find() discover their values in the code above?

Note: Let us ignore things like AsParallel() and AsQueryable() for now.

Answer 1

Here's the code for List<T>.Find (from Reflector):

public T Find(Predicate<T> match) {     if (match == null)     {         ThrowHelper.ThrowArgumentNullException(ExceptionArgument.match);     }     for (int i = 0; i < this._size; i++)     {         if (match(this._items[i]))         {             return this._items[i];         }     }     return default(T); } 

And here's Enumerable.First:

public static TSource First<TSource>(this IEnumerable<TSource> source, Func<TSource, bool> predicate) {     if (source == null)     {         throw Error.ArgumentNull("source");     }     if (predicate == null)     {         throw Error.ArgumentNull("predicate");     }     foreach (TSource local in source)     {         if (predicate(local))         {             return local;         }     }     throw Error.NoMatch(); } 

So both methods work roughly the same way: they iterate all items until they find one that matches the predicate. The only noticeable difference is that Find uses a for loop because it already knows the number of elements, and First uses a foreach loop because it doesn't know it.