从列表中删除项目并同时获取项目

Question

In C# I am trying to get an item from a list at a random index. When it has been retrieved I want it to be removed so that it can't be selected anymore. It seems as if I need a lot of operations to do this, isn't there a function where I can simply extract an item from the list? the RemoveAt(index) function is void. I would like one with a return value.

What I am doing:

List<int> numLst = new List<int>();
numLst.Add(1);
numLst.Add(2);

do
{
  int index = rand.Next(numLst.Count);
  int extracted = numLst[index]; 
  // do something with extracted value...
  numLst.removeAt(index);
}
while(numLst.Count > 0);

What I would like to do:

List<int> numLst = new List<int>();
numLst.Add(1);
numLst.Add(2);

do
{
  int extracted = numLst.removeAndGetItem(rand.Next(numLst.Count)); 
  // do something with this value...
}
while(numLst.Count > 0);

Does such a "removeAndGetItem" function exist?

Answer 1

No, as it's a breach of pure function etiquette, where a method either has a side effect, or returns a useful value (ie not just indicating an error state) - never both.

If you want the function to appear atomic, you can acquire a lock on the list, which will stop other threads from accessing the list while you are modifying it, provided they also use lock :

public static class Extensions
{
    public static T RemoveAndGet<T>(this IList<T> list, int index)
    {
        lock(list)
        {
            T value = list[index];
            list.RemoveAt(index);
            return value;
        }
    }
}

Answer 2

public static class ListExtensions
{
  public static T RemoveAndGetItem<T>(this IList<T> list, int iIndexToRemove}
  {
    var item = list[iIndexToRemove];
    list.RemoveAt(iIndexToRemove);
    return item;
  } 
}

These are called extension methods , call as new List<T>().RemoveAndGetItem(0) .

Things to consider in the extension method

Exception handling with the index that you pass, check that the index is withing 0 and the count of the list before doing this.