Question

I’ve got an IEnumerable<T> as a parameter of a method, where T is a struct type:

using System;
using System.Collections.Generic;
using System.Linq;
using ...

public static class Foo
{
    internal struct CellDiff
    {
        public int RefX;
        public int RefY;
        public object OldValue;
        public object NewValue;
    }

    private static void ItemChanged(IEnumerable<CellDiff> diffs, int cellX, int cellY)
    {
        var change = from CellDiff diff in diffs
                     where diff.RefX == cellX && diff.RefY == cellY
                     select diff;

        ...
    }
}

This results in the following error:

(parameter) IEnumerable<CellDiff> diffs

Error:
Could not find an implementation of the query pattern for source type ‘CellDiff‘. ‘Where‘ not found.

I’ve also tried doing diffs.AsQueryable(), to no avail.

I usually have no problem doing LINQ queries on IEnumerable<T>. I’m a bit lost as to what’s happening here.

Answer 1

Specifying the type in LINQ query syntax creates a call to the Cast extension method with that type argument.

Do you have your own Cast defined somewhere?