Playing with your member

(and: introducing FastMember)

Toying with members. We all do it. Some do it slow, some do it fast.

I am of course talking about the type of flexible member access that you need regularly in data-binding, materialization, and serialization code – and various other utility code.

Background

Here’s standard member access:

Foo obj = GetStaticTypedFoo();
obj.Bar = "abc";

Not very exciting, is it? Traditional static-typed C# is very efficient here when everything is known at compile-time. With C# 4.0, we also get nice support for when the target is not known at compile time:

dynamic obj = GetDynamicFoo();
obj.Bar = "abc";

Looks much the same, eh? But what about when the member is not known? What we can’t do is:

dynamic obj = GetStaticTypedFoo();
string propName = "Bar";
obj.propName = "abc"; // does not do what we intended!

So, we find ourselves in the realm of reflection. And as everyone knows, reflection is slooooooooow. Or at least, it is normally; if you don’t object to talking with Cthulhu you can get into the exciting realms of meta-programming with tools like Expression or ILGenerator – but most people like keeping hold of their sanity, so… what to do?

Middle-ground

A few years ago, I threw together HyperDescriptor; this is a custom implementation of the System.ComponentModel representation of properties, but using some IL instead of reflection – significantly faster. It is a good tool – a worthy tool; but… I just can’t get excited about it now, for various reasons, but perhaps most importantly:

• the weirdness that is System.ComponentModel is slowly fading away into obscurity
• it does not really address the DLR

Additionally, I’ve seen a few bug reports since 4.0, and frankly I’m not sure it is quite the right tool now. Fixing it is sometimes a bad thing.

Having written tools like dapper-dot-net and protobuf-net, my joy of meta-programming has grown. Time to start afresh!

FastMember

So with gleaming eyes and a bottle of Chilean to keep the evil out, I whacked together a fresh library; FastMember – available on google-code and nuget. It isn’t very big, or very complex – it simply aims to solve two scenarios:

• reading and writing properties and fields (known by name at runtime) on a set of homogeneous (i.e. groups of the same type) objects
• reading and writing properties and fields (known by name at runtime) on an individual object, which might by a DLR object

Here’s some typical usage (EDITED - API changes):

var accessor = TypeAccessor.Create(type);
string propName = // something known only at runtime
while( /* some loop of data */ ) {
accessor[obj, propName] = rowValue;
}

or:

// could be static or DLR
var wrapped = ObjectAccessor.Create(obj);
string propName = // something known only at runtime
Console.WriteLine(wrapped[propName]);

Nothing hugely exciting, but it comes up often enough (especially with the DLR aspect) to be worth putting somewhere reusable. It might also serve as a small but complete example for either meta-programming (ILGenerator etc), or manual DLR programming (CallSite etc).

Mary Mary quite contrary, how does your member perform?

So let’s roll some numbers; I’m bundling read and write together here for brevity, but - based on 1M reads and 1M writes of a class with an auto-implemented string property:

Static C#: 14ms
Dynamic C#: 268ms
PropertyInfo: 8879ms
PropertyDescriptor: 12847ms
TypeAccessor.Create: 73ms
ObjectAccessor.Create: 92ms

As you can see, it somewhat stomps on both reflection (PropertyInfo) and System.ComponentModel (PropertyDescriptor), and isn't very far from static-typed C#. Furthermore, both APIs work (as mentioned) with DLR types, which is cute - becaues frankly they are a pain to talk to manually. It also supports fields (vs. properties) and structs (vs. classes, although only for read operations).

That's all; I had some fun writing it; I hope some folks get some use out of it.

Shifting expectations: non-integer shift operators in C#

In C#, it is quite nice that the shift operators (<< and >>) have had their second argument constrained to int arguments, avoiding the oft-confusing piped C++ usage:

cout << "abc" << "def";

But wait a minute! The above line is actually C#, in an all-C# project. OK, I cheated a little (I always do…) but genuinely! This little nugget comes from a stackoverflow post that really piqued my curiosity. All credit here goes to vcsjones, but indeed the line in the documentation about restricting to int (and the return type, etc) is about declaring the operator – not consuming it – so it is seemingly valid for the C# dynamic implementation to use it quite happily.

In fact, the main cheat I used here was simply hiding the assignment of the result, since that is still required. Here’s the full evil:

  using System;

  using System.Dynamic;

  using System.Linq.Expressions;



  class Evil : DynamicObject {

      static void Main() {

          dynamic cout = new Evil();

          var hacketyHackHack =

          cout << "abc" << "def";

      }

      public override bool TryBinaryOperation(

              BinaryOperationBinder binder,

              object arg, out object result) {

          switch(binder.Operation) {

              case ExpressionType.LeftShift:

              case ExpressionType.LeftShiftAssign:

                  // or whatever you want to do

                  Console.WriteLine(arg);

                  result = this;

                  return true;

          }

          return base.TryBinaryOperation(

               binder, arg, out result);

      }

   }

I've seen more evil things (subverting new() via ContextBoundObject is still my favorite evil), but quite dastardly, IMO!

Additional: grrr! I don't know why blogger hates me so much; here it is on pastie.org.

Using dynamic to simplify reflection (and: generic specialization)

As I’ve noted in the past; reflection and generics don’t mix very well. The story isn’t quite as bad in .NET 4 though; here’s an example of something that is just painful to call (for the correct T known only at runtime) in C# 3.0:

And remember – we’re talking about the scenario where T is only known at runtime:

Previously we needed to use lots of MakeGenericMethod (or MakeGenericType) – things like:

You can see how that might quickly become boring. But in .NET 4 / C# 4.0 we can exploit “dynamic” to do all the heavy lifting and cache a delegate per scenario for us:

Much better!

Another possible use of this is generic type specialization:

Now this version is called for `int` arguments, otherwise the generic version is called – just as would have been the case from static C#. Magic!