What is the difference between these two linq implementations?
- by Mahesh Velaga
I was going through Jon Skeet's Reimplemnting Linq to Objects series. In the implementation of where article, I found the following snippets, but I don't get what is the advantage that we are gettting by splitting the original method into two.
Original Method:
// Naive validation - broken!
public static IEnumerable<TSource> Where<TSource>(
this IEnumerable<TSource> source,
Func<TSource, bool> predicate)
{
if (source == null)
{
throw new ArgumentNullException("source");
}
if (predicate == null)
{
throw new ArgumentNullException("predicate");
}
foreach (TSource item in source)
{
if (predicate(item))
{
yield return item;
}
}
}
Refactored Method:
public static IEnumerable<TSource> Where<TSource>(
this IEnumerable<TSource> source,
Func<TSource, bool> predicate)
{
if (source == null)
{
throw new ArgumentNullException("source");
}
if (predicate == null)
{
throw new ArgumentNullException("predicate");
}
return WhereImpl(source, predicate);
}
private static IEnumerable<TSource> WhereImpl<TSource>(
this IEnumerable<TSource> source,
Func<TSource, bool> predicate)
{
foreach (TSource item in source)
{
if (predicate(item))
{
yield return item;
}
}
}
Jon says - Its for eager validation and then defferring for the rest of the part. But, I don't get it.
Could some one please explain it in a little more detail, whats the difference between these 2 functions and why will the validations be performed in one and not in the other eagerly?
Conclusion/Solution:
I got confused due to my lack of
understanding on which functions are
determined to be iterator-generators.
I assumed that, it is based on
signature of a method like
IEnumerable<T>. But, based on the
answers, now I get it, a method is an
iterator-generator if it uses yield
statements.
