C# feature: Add an eval clause to LINQ

[gabrielh]

When writing LINQ queries one often wants to evaluate the result immediately (especially in an multithreaded environments) rather than lazily, so quite often one uses a ToList() or a ToArray():

    (from i in numbers
     where i < 0
     select i*2).ToArray();

Since this requires the use of brackets around the query, the readability advantages of LINQ are reduced and often people drop LINQ and instead use chained extension methods:

     numbers.Where(i => i < 0).Select(i => i*2).ToArray();

The same happens with all methods that exit the monad, e.g. First/Last/Single, Any/All/Contains, Aggregate, Average/Min/Max/Sum, Count, etc.

So wouldn’t it be nice to support an extra clause in LINQ that would let one apply any of these methods to the query?

    from i in numbers
    where i < 0
    select i*2
    eval ToArray();

I am using the eval keyword here as it does actually result in the evaluation of the query.

Similarly for queries on Option/Maybe

    from i in 1.AsOption()
    from j in -2.AsOption()
    select Sqrt(i*j)
    eval Or(0);

More details and a demo are available here

[dsaf]

I see some relation to the forward pipe operator proposal #5445 and also #100.

[JamesTryand]

I think I've just been sick in my mouth.

[svick]

This is a duplicate of #3571 with different name and slightly different syntax.

I think that eval is not a great name, because it's also a name of a well-known function in many other languages which does something completely different.

Also, eval may not actually evaluate the sequence, you could write for example eval AsEnumerable().

[gabrielh]

Duplicate of #3571