Extensions for StructureMap registrations

ExampleRegistry.cs

using StructureMap;
using StructureMap.Configuration.DSL;

public class ExampleRegistry: Registry
{
  public ExampleRegistry()
  {
    For<Interface>().Use<Concrete>()
      .Ctor<string>("connectionString").EqualToConnectionString("connectionStringKey");
  }
}

StructureMapExtensions.cs

using StructureMap;
using StructureMap.Pipeline;
using System.Configuration;

public static class StructureMapExtensions 
{ 
  public static SmartInstance<T> EqualToConnectionString<T>(this SmartInstance<T>.DependencyExpression<string> dependencyExpression, string key)  
  { 
    string connectionString = ConfigurationManager.ConnectionStrings[key].ConnectionString; 
    return dependencyExpression.Is(connectionString); 
  } 
}