Question

Using the query expression style, the let clause can be easily written. My question is how to use the dot notation style to write a let clause.

Answer 1

Essentially it’s a Select (in most cases) which introduces a transparent identifier – via an anonymous type which encapsulates all the currently specified range variables. For example, this query:

string[] names = { "Jon", "Mark" };

var query = from name in names
            let length = name.Length
            where length > 3
            select name + ": " + length;

is translated into something like this:

var query = names.Select(name => new { name, length = name.Length })
                 .Where(z => z.length > 3)
                 .Select(z => z.name + ": " z.length);