Debugging xUnit tests in Xamarin Studio and Mono Develop using The Debugging Trick™

Update: This post has been completely revamped, as it turns out there is much easier way, kudos to Michael for pointing this out. I will lament my image editing skills for a small second :-)

As I mentioned in my recent post on the Splunk blog, we’ve been developing a new awesome portable C# SDK that will support Xamarin/Mono.  We ran into a bunch of issues running on Linux with tests failing due to file paths and supporting pct-encoded URIs, so I decided to try to debug in Xamarin Studio.

I had really hoped this would be easy. It wasn’t as easy I hoped, but it turns out after a bunch of trial and error that there is a pretty simple path.  Xamarin Studio does have a “Debug Application” option, but running that all I could do was run the xUnit console runner, but I couldn’t pass it any parameters. I tried various things for a while and came up empty.

And then I decided to tweet the always helpful Michael Hutchinson to see if he had any ideas, and he did!


Update: It turns out you don’t need to do what is suggested above, and which the first version of this post recommended. 

Read on my friends to find out what you can do…..

First open Xamarin Studio to your test project. You can see I’ve done this below and I’ve added a breakpoint on the completely ridiculous, ficticious test we want to debug.

test project1

Now right click on the project, then select Options->Run->Custom Commands. Next a select Execute in the drop down. And put the following into the Command box.

“/Users/glennblock/xunit/xunit.console.clr4.exe ${TargetFile}”


The first part points to the location of the xunit console runner. The second is an expansion which will get replaced with the test dll.

Now all you have to do is run!



And that my friends is “The Debugging Trick™“!

Side note, I don’t think anyone should have to do this, though this version is far less painful than my first post. I just found out from Michael great news, that there is proper IDE support for xUnit in the works.

Screen Shot 2014-05-14 at 11.29.01 PM

This is very good news! In the meanwhile you have the trick :-).

As a side note this technique is general useful for beyond unit tests, you can use it to debug any managed exe where you need to pass arguments.

Thank you Michael Hutchinson for the help!

Posted in mono, xamarin | Leave a comment

Fluent 2014, Splunk for JavaScript developers, and a dash of Hypermedia

Recently a bunch of my fellow Splunkers and I had the pleasure of attending Fluent 2014 in San Francisco where we held down our Splunk booth. It was a great event!

While at the booth I had the privilege of being interviewed on what Splunk offers of JavaScript developers. It turns out we offer quite a lot. Check out the video to learn more:

It was great to talk to customers that are using or interested in Splunk. Anyone who used it loved it, point blank! Working the both was also a chance to educate developers on what you can do with our developer platform, which our CTO Todd Papaioannou did a great job of in his talk on Big Data and Splunk.

As to the talks, I didn’t get to see many but did see a bunch of keynotes of which here are my favorites (with links where appropriate)

  • Scott Hanselman’s talk entitled “Virtual Machines, Javascript and Assembler“. He did a fantastic and highly entertaining talk (in a way that only Scott can do) on how web (in particular JavaScript and cloud development has radically changed the way we build software, and how it has deeply impacted the Microsoft platform.
  • Lea Verou’s keynote on the “Humble Border-Radius“. I had seen this talk online, but there was something magical about watching it live. It was kind of a comedy show through code, and it had some great information about the design of Border-Radius. Lea is an excellent and engaging speaker.

After the event I managed to sneak in a last minute treat before jumping on a plane. I went to see Mike Amundsen‘s (co-author of RESTful Web APIS) talk on building Hypermedia systems at the API-Craft meetup at Heroku,  Mike speaks with authority, and experience. He discussed the problems hypermedia is trying to solve and then walked through how to build a hypermedia client and server all in JavaScript. There was great conversation after the talk a combination of folks sharing their experiences as well as their skepticism ;-)

And as a bonus I got to see some great friends in the community like Ward Bell (author of Breeze.js), Chris Patterson (author of MassTransit), and Steve Klabnik (author of Designing Hypermedia APIs). I also got to meet some people in person for the first time, namely Mark Foster who has been very active in the ALPS and Blueprint space and Emmanuel Parasakis, the organizer of the meetup.

Shot of Chris, Mike, Chromatic Ward, Steve, Mark, and Emmanuel:


A great way to end a great trip :-)

Posted in splunkdev, Uncategorized | Leave a comment

Extending Splunk’s search language with custom search commands.

I recently blogged on a feature which I worked on, custom search commands for Splunk in our Python SDK. Custom search commands allow you to extend Splunk’s search language with new commands that can do things like apply custom filtering, perform complex mathematical calculations not in the box, or generate events dynamically from an external data source like an external API. Currently we only support them in Python but we’ll be adding more languages in the future.

In the first post of the series I talk about how to build a simple generating command.


Posted in splunkdev | Leave a comment

A discussion on API Documentation and Hypermedia

A few weeks ago, I read a great post from Kin Lane where he was talking about the Open API movement in government. One of the things he discussed was the momentum around APIs and adoption of emerging standards for API documentation. In particular he mentioned Swagger (which I was familiar with), Blueprint, and RAML.

Seeing this traction and being a general fan of helping move the API adoption ball forward, I thought it might be interesting to explore using one of these formats for Splunk’s API. So I decided to wade in to each of the formats and well share my initial thoughts on the best of all places, twitter! Flash forward a bunch of tweets and that turned into a very engaging twitter discussion (or more like a tweetacaine) between Kin, myself and the authors of the different standards, namely Tony Tam (@fehguy) of Swagger, Uri Sarid (@usarid) of RAML, and lastly Jakub Nesteril (@jakubnesetril) of API Blueprint as well others who weighed in like Rob Bihun (@robbihun). This then led to a bunch of us heading to Jabbr where we could stop spamming the rest of the twitterverse and carry on a real conversation.

It was a really interesting discussion where we discussed the goals of each format. Being the hypermedia guy that I am, I was very interested in the level of (or lack of) support for hypermedia in these formats.

After all the discussion it turns out there is a lot of commonality between the different formats:

  • One key thing that came out of the conversation was that all of these standards seem pretty intent on not repeating the mistakes of WSDL. That is the documentation is a guide, and describes a contract, but the description is just to help you, but not a language you must speak to get in the door. And this my friends, is a very GOOD thing!
  • The main difference seems to revolve around the types of capabilities the formats offer, which does impact the conceptual overhead for working with that format. Swagger stands out as trying to be as minimalist as possible, but there is a tradeoff there in how far you can go with it.
  • Another key difference appeared to be around URIs. Swagger appears very much to be centered around the notion of URIs as APIS, while the others seem to take a more resource oriented approach.
  • Blueprint and RAML want to offer more value beyond just docs. Blueprint for example supports Dredd for testing your server API. Blueprint wants to even help you implement your server using the Blueprint doc as a guide for even helping you generate a server implementation.
  • None of the formats (at that time) had any real first class support for hypermedia.

Kin being the awesome guy he is, captured the entire web 2.0ish (if there’s such a thing) discussion from twitter to Jabbr in a recent blog post here. It’s an interesting experiment as it is basically just a capturing of a really large brain dump. It’s like being in the room with us though, everything is there :-)

One thing positive that came out of this discussion is it helped reignite some momentum around first class hypermedia support in API Blueprint and RAML. For Blueprint, there’s an active discussion going on now on a new Resource Blueprint on github here.

Another piece of progress, Kin has had some great further discussions with the creators on the motivations behind their libraries which he’s written up here.

I am really thankful to Kin, Tony, Uri, Jakub and Rob for the great convo!

What are are your experiences around API documentation? Have you used any of these formats? Are you using others?

Regardless, it’s a great time for APIs!

Posted in REST | Tagged | 13 Comments

On Duck Typing

Update: Phil Haack just posted his own reflections on Duck Typing which by the way has a much cooler title than mine!

Another Update: A coworker on my team just passed me an awesome video from Daniel Spiewak describing the fundamentals of type inference. As part of the the talk he describes how structural typing works in Scala. I didn’t realize how much type inference ties in here, but it appears to relate very strongly. Near the end he also talks about Duck Typing as well. If you are a language geek or want to just understand the nuts and bolts, watch it:

Happy New Year everyone!

Recently Eric Lippert (One of the fathers of C#) had a nice post entitled “What is Duck Typing?”. In the post Eric looks at Duck Typing and tries to clarify what it is or isn’t in particular critiquing the Wikipedia article on the topic. His conclusion is that Duck Typing is not a special type system and it is either another name for late-binding or completely meaningless. You should read it!

I’ve been working with Duck Typing for a while, more recently the past few years as I’ve been working mostly with dynamic languages. I agree completely with Eric that it’s not a special type system.  It’s not meaningless though, it is something!

And that leads to this post. I’m going to share my own thoughts on Duck Typing, what it is and what it isn’t, the different types and give examples across several different stacks/languages to back up my points. I’ll also talk about how Duck Tying is evolving in newer stacks like Scala and Go.

What is it?

Duck Typing is a programming technique where a contract is established between a function and its caller, requiring the parameters passed in by the caller to have specific members present.

Update: I found this definition which seems much more accurate than the Wikipedia version: “In a language that supports DuckTyping an object of a particular type is compatible with a method or function, if it supplies all the methods/method signatures asked of it by the method/function at run time.”

There are two types of contracts, Implicit Contracts and Explicit contracts which will both be explored further in this post.

Note: In traditional object-oriented statically typed languages Duck Typing is commonly substituted with using interfaces and inheritance though you can do Duck Typing in many modern static languages.

Is Duck Typing the same as Late Binding?

Duck Typing differs from late binding which is a general term for delaying looking up an object’s members at compile time and doing the lookup at runtime.

Implicit Contracts

In an implicit contract, the contract is implicitly defined solely based on which members of the arguments passed in by the caller, that the code in the function actually accesses.

Dynamic languages

In dynamic languages, Duck Typing is very common. For example the JavaScript snippet below uses Duck Typing. The executeRule function defines a rule as any thing that has an execute function on it.

The contract here is only in the code. The fact that an execute function is invoked in executeRule() means it will fail unless execute() is present.

This kind of code is very easy and common to write in JS due to the very fact that it is dynamic. Similarly you can easily do the same in other dynamic languages like Ruby and Python.

In some stacks these implicit contracts are even formalized as part of the core libraries. For example in nodejs, streams are implicit contracts from a stream implementer perspective. All functions that accept streams are technically using Duck Typing.

What about Method Missing type?

Reading through Phil’s post reminded me that I missed mentioning something. Both Ruby and Javascript have a generic way for dynamically handling invocations on members that are not actually present. Ruby has the method_missing method. Harmony proxies are a bit more complicated but within a proxy you can implement similar semantics. In either case the object (or the proxy) has an explicit implementation to handle missing members. I am kind of back and forth on this one. It obviously not identical in that the presence of the members to satisfy the contract is actually virtualized.  From the standpoint of the function receiving the params it is still Duck Typing though, as it just invokes the members it expects to be present.

Please feel free to disagree with me on this ;-)

Ok, now let’s see Duck Typing in statically typed languages in particular .NET.


VB.NET has had support for using Duck Typing for a long time. As long as your objects are declared as type Object you can party on them in a similar fashion.

C# with dynamic

In C# thanks to the dynamic keyword we can do Duck Typing. What’s nice about this from a C# perspective is you can pass either a dynamic object or a statically typed object and get the same result as long as the required members are present.

Important to note that similar to Ruby and JavaScript you can implement Method Missing type semantics by rolling your own Dynamic Object.


Boo is a really cool statically typed .NET language. Years before dynamic ever existed, Boo introduced the duck type specifically for supporting Duck Typing. Its behavior and dynamic’s are very similar as you can see below.

.NET/JAVA with Reflection

You can even use reflection to achieve the same, but it is far less natural. Basically you use the reflection APIs and invoke members. As Krzysztof Cwalina mentioned in one of this earlier posts, the .NET framework uses this approach for enumerables. Using the previous example, here it is done with reflection in C# (yes this code can be refactored to be more performant).

The same approach can work in Java / any static typed language that has it’s own reflection type APIs.

The downside of this approach is it requires you to do the reflection heavy lifting. Above I am calling a single method, but imagine if I am accessing multiple members, the code starts to get ugly quick. Is it still Duck Typing though? Technically probably yes, but it is definitely not leveraging language features, rather it is utilizing runtime hacks introspection to get the Duck Typing behavior.

Interfaces in traditional static languages

Now the question then becomes is using an interface in C#/Java achieving Duck Typing? Below you can see I introduced an IRule interface, and ExecuteRule now expects an IRule instance.

I would say the answer is no, it is not Duck Typing. The reason it because the object getting passed to the Execute method must explicitly implement an interface in order to be compatible. It is not enough for it to have the Execute method on it’s surface, as in the previous cases.

Explicit Contracts via Structural Typing

In all of the previous examples that were mentioned, we saw two common traits:

  • The contract is established implicitly (in the code)
  • There is no compile time safety.

In recent years, a new player has appeared on the block called Structural Typing which provides a way to do Duck Typing in a compiler safe manner that works with static types.  It is exciting to see these advancements!

Structural Typing has been around for a while in languages like C++ (kudos to Stephen Cleary) and O’Caml (kudos to @PickedUsername for that ref). More recently it has been making an appearance in newer languages like Scala (which Eric mentions in his post), and Go. Similar to Duck Typing, the presence / absence of members on the parameters passed in by the caller determines if the contract is satisfied. The difference however is that the the contract is specified explicitly in a manner that can be used at compile time to ensure compatibility.

In the case of Scala this is done by inlining metadata in the function definition which describes the expected contract.

In Go you can do the same using interfaces. What’s special (and beautiful) about the Go interface which differs from other languages, is it retroactively applies to any object that has the members present in the interface.

In either case the behavior is the same. If E(e)xecuteRule is called passing an object that does not have an E(e)xecute() function it will fail at compile time. The object itself has no knowledge however of the contract though the contract itself is explicitly declared externally.

Summing up

Both Duck Typing and it’s newer cousin Structural Typing are techniques which provide a contract to the caller that is based on the structure of the parameters getting passed in. The contract itself can be implicitly established in code, sacrificing compile time checking, or explicitly by using advancements in newer statically typed languages to get compile time safety.

Parting thought – Now that newer languages are treading the path for achieving duck typing in static typed languages with compiler safety, I hope we see other languages follow suit. I for one would love for C#’s interfaces to work the way they do in Go. The first time I saw the language supported this I was literally drooling. Can you hear me Anders? :-)

Posted in Languages, misc | 20 Comments