Wednesday, 27 May 2009

Exploring 4.0; Expression and Dynamic

You can't have missed that VS2010 beta 1 is now available. With the 4.0 release, most of the changes are in the framework dlls - there aren't a huge amount of C# language changes to pick up. I've done a little dabbling...


I looked previously at Expression on the CTP; well, guess what? They went and renamed everything... here's the previous example, updated; note the use of Expression.Block and Expression.Assign (rather than Comma and AssignProperty):

class Foo
public string Bar { get; set; }
public override string ToString()
return Bar;
static void Main()
var param = Expression.Parameter(typeof(Foo), "foo");
var assign = Expression.Assign(
Expression.Property(param, "Bar"),
Expression.Constant("def", typeof(string)));
var writeLine = Expression.Call(
typeof(Console).GetMethod("WriteLine", new[] { typeof(object) }),

var action = Expression.Lambda<Action<Foo>>(Expression.Block(assign, writeLine), param);
var actionDel = action.Compile();
Foo foo = new Foo();

It is also pretty clear that there are no plans to add language support for this (via a lambda); maybe something for the future.


I think "dynamic" is great if you are talking to COM or DLR; but should generally be avoided otherwise. Still; one interesting aspect is that it provides access to generic operators; which wasn't yet implemented on the last CTP. Well; it is here now - and it actually doesn't perform too badly... to avoid taking a dependency on an extra dll, I'd consider it...

Operator: 833ms (100000010)
Dynamic: 1383ms (100000010)
Operator: 786ms (3.355443E+07)
Dynamic: 1309ms (3.355443E+07)
Operator: 3974ms (100000010)
Dynamic: 3911ms (100000010)
As it happens the Nullable<T>performance isn't quite as good yet, but you can always use MiscUtil's Operator class ;-p

Other than that; unless I start writing lots of IronPython, I currently don't expect to use "dynamic" all that much.