What is the scope of a lambda variable in C#?

Question

I'm confused about the scope of the lambda variable, take for instance the following

var query =      from customer in clist     from order in olist     .Where(o => o.CustomerID == customer.CustomerID && o.OrderDate ==  // line 1         olist.Where(o1 => o1.CustomerID == customer.CustomerID)        // line 2              .Max(o1 => o1.OrderDate)                                  // line 3     )     select new {         customer.CustomerID,         customer.Name,         customer.Address,         order.Product,         order.OrderDate     }; 

In line 1 I have declare a lambda variable 'o' which means I cannot declare it again in line 2 (or at least the compiler complains if I try to) But it doesn't complain about line 3 even though 'o1' already exists??

What is the scope of a lambda variable?

Answer 1

The brackets give the clue - the lambda variable is captured in the scope of where it's declared:

.Where(o => ... olist.Where(o1 => ...).Max(o1 => ...))   //  |----------------------------------------------| scope of o   //                       |---------|                 scope of first o1   //                                      |---------|  scope of second o1 

Note that there's no overlap for the two o1 variables, but they both overlap (or shadow) the o variable and hence can't use the same name.