Question

I’ve begun playing a bit with implementing an IQueryable<T> datatype to query using LINQ. For example I’ve made a couple of functions like this (It is just a temporary detail that the extension method is not for the specific IQueryable implementation):

public static IQueryable<T> Pow<T>(this IQueryable<T> values, T pow) {     var e = BinaryExpression.Power(values.Expression, ConstantExpression.Constant(pow));      return values.Provider.CreateQuery<T>(e); } 

Then I figured it would be useful to apply a function to each element in the IQueryable object but I can’t quite figure out how to construct the proper expression. The method signature could look like this:

public static IQueryable<T> Map<T>(this IQueryable<T> values, Expression<Func<T,T>> map) {     Expression e = ...      return values.Provider.CreateQuery<T>(e); } 

How should I complete this method body?

Answer 1

It seems to me that you are inventing Select. I don’t see the difference between your Map and what Select already does. It returns an IQueryable<U> based on an expression and an initial IQueryable<T>.

For something like Reduce/Fold, see the Queryable.Aggregate function.