c# - Is yield useful outside of LINQ?

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?

Answer

I recently had to make a representation of mathematical expressions in the form of an Expression class. When evaluating the expression I have to traverse the tree structure with a post-order treewalk. To achieve this I implemented IEnumerable like this:

public IEnumerator> GetEnumerator()
{
    if (IsLeaf)

    {
        yield return this;
    }
    else
    {
        foreach (Expression expr in LeftExpression)
        {
            yield return expr;
        }
        foreach (Expression expr in RightExpression)

        {
            yield return expr;
        }
        yield return this;
    }
}

Then I can simply use a foreach to traverse the expression. You can also add a Property to change the traversal algorithm as needed.