Question

i use lots of extension methods like .ToList() and .Reverse() etc without really thinking about what really happens under the covers when i use them. I’ve been searching on google to find out what exactly these methods do, but i can’t seem to find them anywhere. When i use a .toList() in visual studio and i click on “Go to definition” all i see is

         // Summary:
        //     Creates a System.Collections.Generic.List<T> from an System.Collections.Generic.IEnumerable<T>.
        //
        // Parameters:
        //   source:
        //     The System.Collections.Generic.IEnumerable<T> to create a System.Collections.Generic.List<T>
        //     from.
        //
       ...etc

im trying to find out what’s going on inside the (for instance) .Reverse(); method. Does it use a stack, does it simply do something like this … ?

public static List<string> Reverse(List<string> oldList)
{
List<string> newList = new List<string>();    
for (int i = oldList.Count-1; i >= 0; i --)
    {
    newList.Add(oldList[i]);
    }
    return newList;
}

Note: i can’t imagine it’d actually be something like this, but just to clarify my question.

Is there any site/book/whatever that i can check out that shows what exactly these methods do ?

Answer 1

You can configure Visual Studio to load the source code of .Net Framework from Microsoft source servers, when you click ‘Go to Definition’. Here are some instructions: http://referencesource.microsoft.com/downloadsetup.aspx

Note that you don’t have to download the big package, just setting up the options is enough.

Here is the source code of ToList:

    public static List<TSource> ToList<TSource>(this IEnumerable<TSource> source) { 
        if (source == null) throw Error.ArgumentNull("source");
        return new List<TSource>(source); 
    } 

And here is the source code of Reverse:

    public static IEnumerable<TSource> Reverse<TSource>(this IEnumerable<TSource> source) {
        if (source == null) throw Error.ArgumentNull("source"); 
        return ReverseIterator<TSource>(source);
    }

    static IEnumerable<TSource> ReverseIterator<TSource>(IEnumerable<TSource> source) { 
        Buffer<TSource> buffer = new Buffer<TSource>(source);
        for (int i = buffer.count - 1; i >= 0; i--) yield return buffer.items[i]; 
    }