[munchbunny]

LINQ doesn't optimize that much. If you're using LINQ on a database, you may benefit from the underlying database and driver's optimizations. However, if you're just operating on lists and in-memory data structures, you are probably eating the overhead.

As an example, a .Where(...) on a List<...> object is exactly what it claims to be: a linear pass through the list. Sometimes that's exactly what you need. Other times, it's more elegant and fast enough to represent an operation as a list comprehension. Finally, sometimes you really do need to eke out more performance. It's only the last case where LINQ is a bad idea.

[rejschaap]

> As an example, a .Where(...) on a List<...> object is exactly what it claims to be: a linear pass through the list.

Yes, but it uses deferred execution, which means that it returns enough information to perform the filter, it doesn't really do much until you start to enumerate the list. If, for instance, you continue to do a Take(5) on the result, the filter is only applied until it finds 5 elements that satisfy the filter (or until there are no more elements).