C# Language Specification

Select and groupby clauses with continuations

A query expression with a continuation

from … into x …

is translated into

from x in ( from … ) …

The translations in the following sections assume that queries have no into continuations.

The example

from c in customers
group c by c.Country into g
select new { Country = g.Key, CustCount = g.Count() }

is translated into

from g in
from c in customers
group c by c.Country
select new { Country = g.Key, CustCount = g.Count() }

the final translation of which is

customers.
GroupBy(c => c.Country).
Select(g => new { Country = g.Key, CustCount = g.Count() })

2. Explicit range variable types

A from clause that explicitly specifies a range variable type

from T x in e

is translated into

from x in ( e ) . Cast < T > ( )

A join clause that explicitly specifies a range variable type

join T x in e on k₁ equals k₂

is translated into

join x in ( e ) . Cast < T > ( ) on k₁ equals k₂

The translations in the following sections assume that queries have no explicit range variable types.

The example

from Customer c in customers
where c.City == "London"
select c

is translated into

from c in customers.Cast()
where c.City == "London"
select c

the final translation of which is

customers.
Cast().
Where(c => c.City == "London")

Explicit range variable types are useful for querying collections that implement the non-generic IEnumerable interface, but not the generic IEnumerable interface. In the example above, this would be the case if customers were of type ArrayList.

3.