A basic use-case for Task Unwrap

Introduction

Recently, after months without using .Net/C#, I was enhancing an existing .Net/C# WPF application leveraging the .Net Task Parallel Library (TPL).

But naively applying the JavaScript Promises patterns I had used in the previous months I was bitten by a strange issue which forced me to use the quite exotic Unwrap extension method.

This article describes the issue, explains its cause, provides a fix with Unwrap, and finally provides a more modern version with the C# 5.0 async/await paradigm.

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If your plumbing doesn’t work you’re just not using enough pipes

Introduction

The following article is my response to John” comment on my other post about native C++/C# interop using C++/CLI.
The initial request was rather simple: for whatever reason John wanted to use the C++/CLI wrapper from Python and not from native C++.

It seemed technically feasible because Python has a remarkable tool to interact with native code: the ctypes module.
The only issue is that ctypes only supports C interfaces not C++ classes so in this case it can’t directly use the YahooAPIWrapper class.

In fact it’s a minor issue because this kind of situation is well known and a well documented pattern exists to circumvent it: building a C wrapper around the C++ API.

This looks a little crazy because you now have 2 layers between the Python client code and the C# Yahoo API:

Python -> C wrapper -> C++/CLI wrapper -> C# API

Puking rainbow

So, while I don’t think this layering could have any usefulness in real-life, this was a challenging and interesting question.

Looks simple no? Well, as you know when you start to pile up heterogeneous layers unexpected issues can appear and this is exactly what happened there, and it has revealed one that is worth talking about.
So keep reading!

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