如何返回IEnumerable <T> 对于单个项目

Question

I have a function which can return a list of items or a single item like so below ( pseudocode )

IEnumerable<T> getItems()
{
    if ( someCondition.Which.Yields.One.Item )
    {
        List<T> rc = new List<T>();
        rc.Add(MyRC);

        foreach(var i in rc)
            yield return rc;
    }
    else
    {
        foreach(var i in myList)
            yield return i;
    }
}

The 1st part seems a little kludgy, looking to make it readable

Answer 1

IEnumerable<T> getItems()
{
    if ( someCondition.Which.Yields.One.Item )
    {
        yield return MyRC;
    }
    else
    {
        foreach(var i in myList)
            yield return i;
    }
}

Answer 2

You don't need to do anything:

yield return MyRC;

you normally return the items one by one, not grouped in a collection.

But if it's an IEnumerable<IList<T>> then it's different. Simply return this:

yield return new[] { singleItem };

or if it's an IEnumerable<List<T>> then

yield return new List<T> { singleItem };

Answer 3

It's not clear that you need to use an iterator block in the first place. Do you need/want to defer execution? Do you need/want to evaluate the condition multiple times if the caller iterates over the returned sequence multiple times? If not, just use:

IEnumerable<T> GetItems()
{
    if (someCondition.Which.Yields.One.Item)
    {
        return Enumerable.Repeat(MyRC, 1);
    }
    else
    {
        // You *could* just return myList, but
        // that would allow callers to mess with it.
        return myList.Select(x => x);
    }
}

Answer 4

The List<T> is unnecessary. The yield keyword exists for a reason.

IEnumerable<T> getItems(){
    if ( someCondition.Which.Yields.One.Item )
    {
        yield return MyRC;
    }
   else
    {
        foreach(var i in myList)
            yield return i;
    }
}

Answer 5

What about:

 IEnumerable<T> getItems(){ 
    if ( someCondition.Which.Yields.One.Item ) 
    { 
        yield return MyRC; 
    } 
    else 
    { 
        foreach(var i in myList) 
           yield return i; 
    }