Is it possible to extend the Query-Keywords in C# / LINQ?

Question

is it possible to extend the query-keywords of Linq (like: select, where, etc.) with own definitions?

Codeexample to make it clearer:

System.Collections.Generic.List<string> aList = 
    new System.Collections.Generic.List<string> { "aa", "ab", "ba", "bb" };

// instead of
string firstString = (from item in aList
                      where item.StartsWith("a")
                      select item).First();

// would be nice
string firstString = from item in aList
                     where item.StartsWith("a")
                     selectFirst item;

// or something else
from item in aList
where item.StartsWith("a")
WriteLineToConsole item;

I think it's not possible, but still hoping ;)

Answer 1

You can't add your own contextual keywords, but you can affect what the existing ones mean.

For example, this code:

string firstString = (from item in aList
                      where item.StartsWith("a")
                      select item).First();

is effectively preprocessed to:

string firstString = aList.Where(item => item.StartsWith("a"))
                          .First();

... so if you change what those Where and First method calls mean, you can affect the behaviour.

If you've got the stomach for it, you might want to look at this Stack Overflow answer I wrote a while ago which changes the behaviour of where in LINQ to Entities in certain circumstances. It's evil, evil code though.