CODEWITHSUNDEEP
c#.net
Julien Lebot
Julien Lebot

Reputation: 3092

System.Collections.Stack.Peek() vs FirstOrDefault()

Recently I have seen a colleague use FirstOrDefault() when interacting with a Stack instead of Peek().

It had never crossed my mind to use an extension method instead of the built-in Peek(), and I'm wondering what are the implications / differences between the two.

Is one recommended over the other ? Looking with ildasm.exe didn't teach me anything useful.

Upvotes: 3

Views: 1372

Answers (2)

shat90
shat90

Reputation: 405

To quote from MSDn https://msdn.microsoft.com/en-us/library/system.collections.stack.peek%28v=vs.110%29.aspx

Firstly

Peek() is an O(1) operation

FirstOrDefault() works as follows according to Reflector and is a more expensive operation.

public static TSource FirstOrDefault<TSource>(this IEnumerable<TSource> source)
{
   if (source == null)
{
    throw Error.ArgumentNull("source");
}
IList<TSource> list = source as IList<TSource>;
if (list != null)
{
    if (list.Count > 0)
    {
        return list[0];
    }
}
else
{
    using (IEnumerator<TSource> enumerator = source.GetEnumerator())
    {
        if (enumerator.MoveNext())
        {
            return enumerator.Current;
        }
    }
}
return default(TSource);
}

Secondly,

Peek errors out at an empty stack, FirstOrDefault returns a null value though First() would also error out.

Upvotes: 2

Servy
Servy

Reputation: 203844

FirstOrDefault will return the default value for T if the stack is empty; Peek will throw.

That's about it as far as functional changes. FirstOrDefault adds a few layers of indirection, creating an enumerable/enumerator object (which will eventually need to be disposed of), computing whether there are more items, fetching the first item through the enumerable, and then returning it, rather than having the stack itself do only the necessary operations. While this is technically more work, it's highly unlikely for that to be enough to matter in the vast majority of situations.

Upvotes: 8

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