But here's a microbenchmark[1]. It's still not close to non-LINQ code. A factor of 10, with a trivial body, just summing up some numbers. (I didn't used Sum() as it appears to use checked arithmetic.)
As far as the optimizations, the smart combining code (which still has to allocate a combined delegate + lambda object, that'll cost, what 2 objects at like 40 bytes each?)) only happens when Select is followed by Select, or Where by Where. Select after Where gets a new "WhereSelectEnumerableIterator" and so on.
So you're right that it does eliminate some overhead though depending on the order of your Wheres and Selects there may be more "foreach" loops in the comparable code. And it's still not even close to being free like it should be. (Like, say, Haskell can do sometimes.)
But here's a microbenchmark[1]. It's still not close to non-LINQ code. A factor of 10, with a trivial body, just summing up some numbers. (I didn't used Sum() as it appears to use checked arithmetic.)
As far as the optimizations, the smart combining code (which still has to allocate a combined delegate + lambda object, that'll cost, what 2 objects at like 40 bytes each?)) only happens when Select is followed by Select, or Where by Where. Select after Where gets a new "WhereSelectEnumerableIterator" and so on.
So you're right that it does eliminate some overhead though depending on the order of your Wheres and Selects there may be more "foreach" loops in the comparable code. And it's still not even close to being free like it should be. (Like, say, Haskell can do sometimes.)
1: http://pastebin.com/7J9FErWN