[curveship]

With all respect, it doesn't sound like you've taken the time to understand LINQ:

- Single and SingleOrDefault crashing with >1 row is a feature, not a bug. It means that your expectation that your filter is unique was incorrect. In that scenario, a crash is what you want. It's like when we use asserts. Similarly ..

- First and FirstOrDefault are only really appropriate after an OrderBy, i.e. to get the top item of a particular ranking. Using them anywhere else is almost always incorrect, and in the very few cases where it isn't, needs a comment to explain why, or I'll bounce your code back to you in review :).

LINQ is very expressive (you can do a lot with a little bit of code), especially with the embedded (non-fluent) syntax. That means that, yes, you can write some non-optimal code without realizing it, because it's only a few lines. On the flip side, you can also refactor that code quickly into more optimal patterns. By comparison, old-school iterating through collections is often much more difficult to refactor.

[batou]

I understand LINQ very well (right down to code generation and expression trees) but unfortunately I work with a lot of other people's code.

Perhaps that is the problem? :-)

More seriously, the thing has really leaky abstraction boundaries which is a main pain point. I have to write and manage a lot of boring enterprise code and creativity and expressiveness go a long way to introducing a lot of additional work.

[nlawalker]

LINQ is not where the leaky abstraction is, IEnumerable is. IEnumerable makes virtually no guarantees about anything, including order, finiteness, side effects and speed/efficiency.

This is actually one of the main reasons that the BCL team introduced the IReadOnlyXXX<> interfaces - over the years, many .NET developers trying to do the right thing and express intent in their code had taken to using IEnumerable<> in method signatures to signify that the method would not modify the list/collection... but an IEnumerable doesn't have to be a list/collection, it can be infinite! In trying to do the right thing and be expressive with intent, lots and lots of people were unwittingly losing the expression of another (very important) assumption.

Any time you are wrangling any kind of enumerable in code, you have to think about its guarantees and assumptions. LINQ's expressiveness might make it easier to forget this but it's still the rule - if I hand you a "malicious IEnumerable", it doesn't matter if you use LINQ or a couple of foreach loops, it's going to launch the missiles on every call to MoveNext() regardless.

If you are trying to express intent in your code, IEnumerable is almost never what you want to use.