RoslynDifference2.cs

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

public static class C {
    public static void M(object[] items) {
        var cancelableItems = items.Cast<dynamic>()
                                   .Where(d => d.CanCancel())
                                   .ToArray();

        //
        // o.OrderId dynamically bound without problem with csc.exe in VS2013.
        //
        var tasks1 = cancelableItems.ToArray(o => F((long)o.OrderId));

        //
        // Works fine if lambda parameter is explicitly typed.
        //
        var tasks2 = cancelableItems.ToArray((dynamic o) => F((long)o.OrderId));
    }
    
    private static long F(long id) {
        return id;
    }
    
    public static TResult[] ToArray<TResult>(this IEnumerable items, Func<object, TResult> selector)
    {
        return ToArray(items.Cast<object>(), selector);
    }

    public static TResult[] ToArray<TSource, TResult>(this IEnumerable<TSource> items, Func<TSource, TResult> selector)
    {
        return items.Select(selector).ToArray();
    }
}