返回多个项目

Question

How can I make a bool function return something alongside the bool? An example would be:

public bool MyBool(List<Item> a, string lookfor)
{

  foreach(Item it in a)
  {

    if(it.itemname == look for)
    {
      //Also return the item that was found!
      return true;
    }

  }
  return false;

}

So basically if something is true, I would also like to return that item alongside the bool. Is that possible?

Answer 1

Basically, two options.

The first, return a result using out parameter modifier ( more info on MSDN )

public bool MyBool(List<Item> a, string lookfor, out Item result)

or the second, return a result packed into Tuple

public Tuple<bool, Item> MyBool(List<Item> a, string lookfor)

Answer 2

You need an out parameter passed in the call, out parameters are expected to be set by the called method. So, for example, you could have something like this

public bool MyBool(List<Item> a, string lookfor, out Item found)
{
    found = a.SingleOrDefault(it => it.itemname == lookfor);
    return found != null;
}

in the calling code you could write

Item it;
if(ClassInstanceWithMethod.MyBool(ListOfItems, "itemToSearchFor", out it))
    Console.WriteLine(it.itemname);

However, I recommend to change the name of this method to something more obvious
(TryGetValue seems to be a perfect fit)

Answer 3

You would use the out keyword on a parameter. Here is a real world example from Dictionary<TKey,TValue>

public bool TryGetValue(TKey key, out TValue value)
{
    int index = this.FindEntry(key);
    if (index >= 0)
    {
        value = this.entries[index].value;
        return true;
    }
    value = default(TValue);
    return false;
}