How to implement a C# concept exercise

January 28, 2021 · View on GitHub

This document describes how to implement a concept exercise for the C# track.

Please please please read the docs before starting. Posting PRs without reading these docs will be a lot more frustrating for you during the review cycle, and exhaust Exercism's maintainers' time. So, before diving into the implementation, please read the following documents:

Please also watch the following video:

The Anatomy of a Concept Exercise.

As this document is generic, the following placeholders are used:

<SLUG>: the slug of the exercise in kebab-case (e.g. calculator-conundrum).
<NAME>: the name of the exercise in PascalCase (e.g. CalculatorConundrum).
<CONCEPT_SLUG>: the slug of one of the exercise's concepts in kebab-case (e.g. anonymous-methods).

Before implementing the exercise, please make sure you have a good understanding of what the exercise should be teaching (and what not). This information can be found in the exercise's GitHub issue. Having done this, please read the C# concept exercises introduction.

To implement a concept exercise, the following files must be added:

languages
└── csharp
    ├── concepts
    |   └── <CONCEPT_SLUG>
    |       ├── about.md
    |       └── links.json
    └── exercises
        └── concept
            └── <SLUG>
                ├── .docs
                |   ├── instructions.md
                |   ├── introduction.md
                |   ├── hints.md
                |   └── source.md (required if there are third-party sources)
                ├── .meta
                |   |── config.json
                |   |── design.md
                |   └── Exemplar.cs
                ├── <NAME>.cs
                ├── <NAME>.csproj
                └── <NAME>Tests.cs

Step 1: Add code files

The code files are track-specific and should be designed to help the student learn the exercise's concepts. The following C# code files must be added (not necessarily in this order):

Add `<NAME>.cs` file

Purpose: Provide a stub implementation.

The stub implementation's code should compile. The only exception is for exercises that introduce syntax we want a student to define themselves, like how to define a class or property. In this case, insert a descriptive TODO comment instead of providing stub code (see this example).
Stub methods should throw a NotImplementedException which message contains the method to implement, see this instance method example. The message is subtly different for static stub methods, see this static method example.

For more information, please read this in-depth description, watch this video and check this example stub file.

Add `<NAME>Tests.cs` file

Purpose: The test suite to verify a solution's correctness.

xUnit is used as the test framework.
Only use Fact tests; don't use Theory tests.
All but the first test should be skipped by default (check this example).
Test methods must be named using snake_case, with the first character uppercased (check this example).
Test methods must have a single assertion.

For more information, please read this in-depth description, watch this video and check this example tests file.

Add `<NAME>.csproj` file

Purpose: The project file required to build the project and run the tests.

For more information, check this example project file.

Add `.meta/Exemplar.cs` file

Purpose: The idiomatic example implementation that passes all the tests.

For more information, please read this in-depth description, watch this video and check this example file.

Step 2: Add documentation files

How to create the files common to all tracks is described in the how to implement a concept exercise document.

Step 3: Update list of implemented exercises

Add the exercise to the list of implemented exercises.

Step 4: format code

All C# code should be formatted using the dotnet format tool. There are two ways to format your C# code:

1. Using a GitHub comment

If you add a comment to a GitHub PR that contains the text /dotnet-format, a GitHub workflow will format all C# documents in the PR using dotnet format. Any formatting changes made by dotnet format will automatically be committed to the PR's branch. This also works for forks that have enabled maintainers to edit the fork's PR (which is the default).

2. Using a script

Open a command prompt in the language/csharp directory and then run:

./format.ps1 <SLUG>, where <SLUG> is the exercise's directory name.

When implementing an exercise, it can be very useful to look at already implemented C# exercises like the log-levels, datetimes or floating-point numbers exercises. You can also check the exercise's general concepts documents to see if other languages have already implemented an exercise for that concept.

Help

If you have any questions regarding implementing the exercise, please post them as comments in the exercise's GitHub issue.