Why does compiler generate different classes for anonymous types if the order of fields is different

Question

I've considered 2 cases:

var a = new { a = 5 };
var b = new { a = 6 };
Console.WriteLine(a.GetType() == b.GetType()); // True

Ideone: http://ideone.com/F8QwHY

and:

var a = new { a = 5, b = 7 };
var b = new { b = 7, a = 6 };
Console.WriteLine(a.GetType() == b.GetType()); // False

Ideone: http://ideone.com/hDTcxX

The question is why does order of fields actually matter?

Is there any reason for this or it's just simply because it is (such is the design).

If the reason is just that anonymus types are not supposed to be used this way and you are not supposed to appeal to GetType, then why does compiler re-use a single class in first case and not just generate a new class for each anonymus type declaration?

Answer 1

So the reason for the design decision was ToString. An anonymous type returns a different string accoding to the order. Read Eric Lippert's blog.

{ a = 5, b = 7 }
{ b = 7, a = 6 }

Demo