Can anyone please tell me the difference between the following two lambda expressions:
1. TabView mytab = TabCollection.Where(s => s.TabHeader == h).FirstOrDefault();
2. TabView mytab = TabCollection.FirstOrDefault(s => s.TabHeader == h);
TabCollection is an ObservableCollection of type TabView.
The two statements will provide the same results.
The difference is in how the result is achieved. The second is slightly more efficient, as it does not need to generate an iterator for the Where method, and then get it's enumerator, and can instead directly enumerate the collection until a match is found.
FirstOrDefault starts enumerating the IEnumerable<T> returned from Where, it enumerates it in a deferred, streaming manner. Both versions will still short circuit and stop checking once a match is found.Where does not need to check every item - it will only check items as FirstOrDefault enumerates them, which means it'll only check until a match is found and then stop.TabCollection.Where(s => s.TabHeader == h).FirstOrDefault()
This creates WhereIterator and returns it. Then you starting iteration and return first element of it. That looks like
var iterator = new WhereEnumerableIterator<TSource>(TabCollection, predicate);
using (IEnumerator<TSource> enumerator = iterator.GetEnumerator())
{
if (enumerator.MoveNext())
return enumerator.Current;
}
return default(TSource);
Second one does not create iterator - it simply enumerates over source:
TabCollection.FirstOrDefault(s => s.TabHeader == h);
Same as
foreach (TSource local in TabCollection)
{
if (predicate(local))
return local;
}
return default(TSource);
So, second option is slightly more efficient.
Less code + same results=Better Code. Use the second approach. type less. delay carpal tunnel.Wherequery lazily, so on each iteration or method call it could yield a different result. You could also chain other linq methods if desired(e.g.OrderByorTake(n)) whereas theFirstOrDefault"ends" the query. However, the second approach is a little bit more effficient and - more important - more readable since it's more direct.