Dutton's blog

I came across a problem during recent round of refactoring. Here's a contrived simiIar example.

I have an IEnumerable, MyThings contains a property of type Enum called MyThingType. Scattered around my class I found I had quite a bit of duplicated code consisting of a Linq Where statement to filter the IEnumerable based on a specific values of MyThingType and then perform some additional actions on the result.

var filtereredThings = MyThingsList.Where(t => t.MyThingType == ThingType.ThingA);
// other stuff on filteredThings

All good so far, I extracted the common code into a new private method call which returned my result and took the MyThingType as a parameter to filter on, the problem arose when my last Where statement filtered on two MyThingType values.

private IEnumerable FilterAndProcessThingType(IEnumerable data, ThingType filterType)
{
  var filtereredThings = MyThingsList.Where(t => t.MyThingType == filterType);
  // other stuff on filteredThings and return result
}

I changed my method to take a params parameter for the filter so I can pass a variable number of MyThingType in, but how do I change my Linq?

private IEnumerable FilterAndProcessThingType(IEnumerable data, params ThingType[] filterType)
{
  var filtereredThings = MyThingsList.Where(t => t.MyThingType == ???);
  // other stuff on filteredThings and return result
}

This is where Predicate comes in; a Predicate is a function which returns true or false. This means I can dynamically create one to do my MyThingType check and put it in my Where's Lambda expression.

private IEnumerable FilterAndProcessThingType(IEnumerable data, params ThingType[] typeFilter)
{
  var thingTypeMatcher = new Predicate<tuple<thingtype, thingtype[]="">>(t =>
  {
    var thingType = t.Item1;
    var thingTypeArray = t.Item2;
    return thingTypeArray.Aggregate(false,(current, type) => current | thingType == type);
  });
  var filtereredThings = MyThingsList.Where(t => thingTypeMatcher(new Tuple<thingtype, thingtype[]="">(t.MyThingType, typeFilter));
  // other stuff on filteredThings and return result
}

And that's it, now I can pass a variable number of types to match into my common code.

I use an iMac at home, so any Windows development is done in a Windows 8 virtual machine running under VMWare Fusion 4.1.4.

I ran into a problem this evening when playing around with some Windows Phone 8 development and thought I'd share the solution. It turns out the default Fusion configuration doesn't support the hardware assisted visualization (Hyper-V) that the Windows Phone SDK Phone Simulator uses.

Not to worry, just do the following (works for me under 4.1.4).

• Shutdown the virtual machine.
• From the Virtual Machine Library Ctrl-Click on the virtual machine's icon and select Show in finder.
• Ctrl-click on the vm's bundle under Finder and click Show Package Contents.
• In there you will find a .vmx file, this is the virtual machine's configuration file. Open this in your favorite editor.
• Add the following two lines to the end of the file:

vhv.enable = "TRUE"
hypervisor.cpuid.v0 = "FALSE"

• Save the file, restart your VM and the Phone Simulator will work fine.

NB: My VM has two processors, I haven't tried this on a single process VM yet.