Compiler optimizations of anonymous types

Question

OK OK, I know this is a hack, but this was for a tiny data-manipulation project and I wanted to play around. ;-)

I was always under the impression that the compiler would examine all anonymous types used in a C# program and if the properties were the same, it would only create one class behind the scenes.

So let's say I want to create an anonymous type out of some typed datasets that I have:

var smallData1 = new smallData1().GetData().Select(
    x => new { Name = x.NAME, x.ADDRESS, City = x.CITY, State = x.STATE,
    Zip = x.ZIP, Country = x.COUNTRY, ManagerName = x.MANAGER_NAME,
    ManagerID = x.MANAGER_ID });

var smallData2 = new smallData2().GetData().Select(
    x => new { x.Name, x.ADDRESS, x.City, x.State, x.Zip, x.Country,
    x.ManagerName,x.ManagerID });

I can now do fun things like smallData2.Except(smallData1); etc., and it all works.

Now, what if I have a bigger pair of anonymous types:

var bigData1 = new BigAdapter1().GetData().Select(
    x => new { x.FirstName, x.LastName, x.Address, x.City, x.State,
    x.Zip, x.Country, x.Phone, x.Email, x.Website, x.Custom1, x.Custom2,
    x.Custom3, x.Custom4, x.Custom5, x.Custom6, x.Custom7, x.Custom8, x.Custom9,
    x.Custom10, x.Custom11, x.Custom12, x.Custom13, x.Custom14, x.Custom15,
    x.Custom16, x.Custom17, x.Custom18, x.Custom19, x.Custom20, x.Custom21,
    x.Custom22, x.Custom23, x.Custom24, x.Custom25, x.Custom26, x.Custom27,
    x.Custom28, x.Custom29});

var bigData2 = new BigAdapter2().GetData().Select(
    x => new { x.FirstName, x.LastName, x.Address, x.City, x.State, x.Zip,
    x.Country, x.Phone, x.Email, x.Website, x.Custom1, x.Custom2, x.Custom3,
    x.Custom4, x.Custom5, x.Custom6, x.Custom7, x.Custom8, x.Custom9, x.Custom10,
    x.Custom11, x.Custom12, x.Custom13, x.Custom14, x.Custom15, x.Custom16,
    x.Custom17, x.Custom18, x.Custom19, x.Custom20, x.Custom21, x.Custom22,
    x.Custom23, x.Custom24, x.Custom25, x.Custom26, x.Custom27,
    x.Custom28, x.Custom29});

Now when I do bigData2.Except(bigData1); the compiler complains:

Instance argument: cannot convert from
'System.Data.EnumerableRowCollection<AnonymousType#1>' to
'System.Linq.IQueryable<AnonymousType#2>'

Why? Too many properties, so the compiler decides it's not worth it to optimize?

Thanks!

Answer 1

Yep. Its not the number of properties. How sure are you that your adapters are returning exactly the same data types?

Answer 2

Have you tried

bigData2.Except(bigData1.AsQueryable());

I've just run a LINQ example with 40 properties and 20,000,000 rows and I don't run into an issue.

(Try this unfortunately not collapsible example in LINQPad)

void Main()
{
 Test t = new Test();
 var a = Enumerable.Range(1,10000000).Select(i => new  
 { 
  t.T0, t.T1, t.T2, t.T3, t.T4, t.T5, t.T6, t.T7, t.T8, t.T9,
  t.T10, t.T11, t.T12, t.T13, t.T14, t.T15, t.T16, t.T17, t.T18, t.T19,
  t.T20, t.T21, t.T22, t.T23, t.T24, t.T25, t.T26, t.T27, t.T28, t.T29,
  t.T30, t.T31, t.T32, t.T33, t.T34, t.T35, t.T36, t.T37, t.T38, t.T39,
 });

 Test2 t2 = new Test2();
 var b = Enumerable.Range(1,10000000).Select(i => new  
 { 
  t2.T0, t2.T1, t2.T2, t2.T3, t2.T4, t2.T5, t.T6, t2.T7, t2.T8, t2.T9,
  t2.T10, t2.T11, t2.T12, t2.T13, t2.T14, t2.T15, t2.T16, t2.T17, t2.T18, t2.T19,
  t2.T20, t2.T21, t2.T22, t2.T23, t2.T24, t2.T25, t2.T26, t2.T27, t2.T28, t2.T29,
  t2.T30, t2.T31, t2.T32, t2.T33, t2.T34, t2.T35, t2.T36, t2.T37, t2.T38, t2.T39,
 });

 a.Except(b).Dump();
}

class Test
{
 public string T0 { get; set ;}
 public string T1 { get; set ;}
 public string T2 { get; set ;}
 public string T3 { get; set ;}
 public string T4 { get; set ;}
 public string T5 { get; set ;}
 public string T6 { get; set ;}
 public string T7 { get; set ;}
 public string T8 { get; set ;}
 public string T9 { get; set ;}
 public string T10 { get; set ;}
 public string T11 { get; set ;}
 public string T12 { get; set ;}
 public string T13 { get; set ;}
 public string T14 { get; set ;}
 public string T15 { get; set ;}
 public string T16 { get; set ;}
 public string T17 { get; set ;}
 public string T18 { get; set ;}
 public string T19 { get; set ;}
 public string T20 { get; set ;}
 public string T21 { get; set ;}
 public string T22 { get; set ;}
 public string T23 { get; set ;}
 public string T24 { get; set ;}
 public string T25 { get; set ;}
 public string T26 { get; set ;}
 public string T27 { get; set ;}
 public string T28 { get; set ;}
 public string T29 { get; set ;}
 public string T30 { get; set ;}
 public string T31 { get; set ;}
 public string T32 { get; set ;}
 public string T33 { get; set ;}
 public string T34 { get; set ;}
 public string T35 { get; set ;}
 public string T36 { get; set ;}
 public string T37 { get; set ;}
 public string T38 { get; set ;}
 public string T39 { get; set ;}
}

class Test2
{
 public string T0 { get; set ;}
 public string T1 { get; set ;}
 public string T2 { get; set ;}
 public string T3 { get; set ;}
 public string T4 { get; set ;}
 public string T5 { get; set ;}
 public string T6 { get; set ;}
 public string T7 { get; set ;}
 public string T8 { get; set ;}
 public string T9 { get; set ;}
 public string T10 { get; set ;}
 public string T11 { get; set ;}
 public string T12 { get; set ;}
 public string T13 { get; set ;}
 public string T14 { get; set ;}
 public string T15 { get; set ;}
 public string T16 { get; set ;}
 public string T17 { get; set ;}
 public string T18 { get; set ;}
 public string T19 { get; set ;}
 public string T20 { get; set ;}
 public string T21 { get; set ;}
 public string T22 { get; set ;}
 public string T23 { get; set ;}
 public string T24 { get; set ;}
 public string T25 { get; set ;}
 public string T26 { get; set ;}
 public string T27 { get; set ;}
 public string T28 { get; set ;}
 public string T29 { get; set ;}
 public string T30 { get; set ;}
 public string T31 { get; set ;}
 public string T32 { get; set ;}
 public string T33 { get; set ;}
 public string T34 { get; set ;}
 public string T35 { get; set ;}
 public string T36 { get; set ;}
 public string T37 { get; set ;}
 public string T38 { get; set ;}
 public string T39 { get; set ;}
}