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When ever I think I can use the yield keyword, I take a step back and look at how it will impact my project. I always end up returning a collection instead of yeilding because I feel the overhead of maintaining the state of the yeilding method doesn't buy me much. In almost all cases where I am returning a collection I feel that 90% of the time, the calling method will be iterating over all elements in the collection, or will be seeking a series of elements throughout the entire collection.
I do understand its usefulness in linq, but I feel that only the linq team is writing such complex queriable objects that yield is useful.
Has anyone written anything like or not like linq where yield was useful?
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You use a yield return statement to return each element one at a time. The sequence returned from an iterator method can be consumed by using a foreach statement or LINQ query. Each iteration of the foreach loop calls the iterator method.
The yield keyword is use to do custom stateful iteration over a collection. The yield keyword tells the compiler that the method in which it appears is an iterator block. yield return <expression>; yield break; The yield return statement returns one element at a time.
The yield keyword performs custom and stateful iteration and returns each element of a collection one at a time sans the need of creating temporary collections. The yield keyword, first introduced in C# 2.0, T returns an object that implements the IEnumerable interface.
As written it is thread safe but if you comment out the lock(_sync) in AllValues you should be able to verify that it is not thread safe by running it a few times.
Note that with yield, you are iterating over the collection once, but when you build a list, you'll be iterating over it twice.
Take, for example, a filter iterator:
IEnumerator<T> Filter(this IEnumerator<T> coll, Func<T, bool> func) { foreach(T t in coll) if (func(t)) yield return t; } Now, you can chain this:
MyColl.Filter(x=> x.id > 100).Filter(x => x.val < 200).Filter (etc) You method would be creating (and tossing) three lists. My method iterates over it just once.
Also, when you return a collection, you are forcing a particular implementation on you users. An iterator is more generic.
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