Implement new concept exercise for extension methods

concepts/extension-methods/.meta/config.json

@@ -0,0 +1,6 @@
+{
+  "blurb": "Extension methods allow you to add methods to existing types.",
+  "authors": [
+    "yzAlvin"
+  ]
+}

concepts/extension-methods/about.md

@@ -0,0 +1,20 @@
+# About
+
+[Extension methods][extension-methods] allow adding methods to existing types without creating a new derived type, recompiling, or otherwise modifying the original type.
+
+Extension methods are static methods, but they're called as if they were instance methods on the extended type. It achieves this by using `this` before the type, indicating the instance we put the `.` on is passed as the first parameter. For client code, there's no apparent difference between calling an extension method and the methods defined in a type.
+
+```csharp
+public static int WordCount(this string str)
+{
+    return str.Split().Length;
+}
+
+"Hello World".WordCount();
+// => 2
+```
+
+A well-known example of extension methods are the [LINQ][linq] standard query operators that add query functionality to the existing IEnumerable types.
+
+[linq]: https://docs.microsoft.com/en-us/dotnet/csharp/programming-guide/concepts/linq/
+[extension-methods]: https://docs.microsoft.com/en-us/dotnet/csharp/programming-guide/classes-and-structs/extension-methods

concepts/extension-methods/introduction.md

@@ -0,0 +1,13 @@
+# Introduction
+
+Extension methods allow adding methods to existing types without creating a new derived type, recompiling, or otherwise modifying the original type. They are defined as static methods but are called by using instance method syntax. Their first parameter is preceded by the 'this' modifier, and specifies which type the method operates on.
+
+```csharp
+public static int WordCount(this string str)
+{
+    return str.Split().Length;
+}
+
+"Hello World".WordCount();
+// => 2
+```

concepts/extension-methods/links.json

@@ -0,0 +1,6 @@
+[
+  {
+    "url": "https://docs.microsoft.com/en-us/dotnet/csharp/programming-guide/classes-and-structs/extension-methods",
+    "description": "extension-methods"
+  }
+]

config.json

@@ -420,6 +420,17 @@
           "overflow",
           "integral-numbers"
         ]
+      },
+      {
+        "slug": "log-analysis",
+        "name": "Log Analysis",
+        "uuid": "4a940e54-eda8-4500-bcb2-25d83af01fb1",
+        "concepts": ["extension-methods"],
+        "prerequisites": [
+          "collections",
+          "strings",
+          "booleans"
+        ]
       }
     ],
     "practice": [

exercises/concept/calculator-conundrum/CalculatorConundrum.cs

@@ -15,7 +15,7 @@ public static int Division(int operand1, int operand2)
     {
         return operand1 / operand2;
     }
-
+    
     public static int Multiplication(int operand1, int operand2)
     {
         return operand1 * operand2;

exercises/concept/log-analysis/.docs/hints.md

@@ -0,0 +1,4 @@
+# Hints
+
+All extension methods must be marked static
+All extension methods must mark `this` for the first argument

exercises/concept/log-analysis/.docs/instructions.md

@@ -0,0 +1,35 @@
+# Instructions
+
+In this exercise you will be adding extension-methods on the string type to make it easier to deal with logs. Extension-methods express intent of the code, make code more readable, and add common functionality.
+
+The goal is to add extension-methods that abstract away the logic of finding out certain things about the log messages.
+
+```csharp
+var log = "[Error]: {Line 20} - 'Critical error found'";
+
+log.WordCount(); // => returns 7
+
+log.LogLevel(); // => returns "Error"
+
+log.LogLine(); // => returns "20"
+
+log.Truncate(10); // => returns "[Error]: {Line 20} - 'Critical error found'"
+
+log.Truncate(5); // => returns "Error - 20"
+```
+
+## 1. Implement the extension method WordCount
+
+Implement the `.Word()` method to return the total of all words in the string. A 'word' in this case is just any string separated by a space.
+
+## 2. Implement the extension method LogLevel
+
+Implement the `.LogLevel()` method to return the log level of the log string.
+
+## 3. Implement the extension method LogLine
+
+Implement the `.LogLine()` method to return the line the log occured at of the log string.
+
+## 4. Implement the extension method Truncate
+
+Implement the `.Truncate(int maxSize)` method to return the log message truncated to "loglevel - logline" if the message exceeds the maximum word count specified, otherwise return the original log message.

exercises/concept/log-analysis/.docs/introduction.md

@@ -0,0 +1,21 @@
+# Introduction
+
+Extension methods allow adding methods to existing types without creating a new derived type, recompiling, or otherwise modifying the original type.
+
+```csharp
+public static bool IsEven(this int number)
+{
+    return number % 2 == 0;
+}
+
+int isEven = 3.IsEven();
+// isEven == false
+
+public static int WordCount(this string str)
+{
+    return str.Split().Length;
+}
+
+int wordCount = "Hello World!".WordCount();
+// wordCount == 2
+```

exercises/concept/log-analysis/.meta/Exemplar.cs

@@ -0,0 +1,18 @@
+using System;
+
+public static class LogAnalysis 
+{
+    public static int WordCount(this string log) =>
+        log.Split().Length;
+
+    public static string LogLevel(this string log) =>
+        log.Substring(log.IndexOf("[") + 1, log.IndexOf("]") - 1);
+
+    public static string LogLine(this string log) =>
+        log.Substring(log.IndexOf("{") + 6, log.IndexOf("}") - (log.IndexOf("{") + 6));
+
+    public static string Truncate(this string log, int maxSize) =>
+        log.WordCount() < maxSize
+        ? log
+        : $"{log.LogLevel()} - {log.LogLine()}";
+}

exercises/concept/log-analysis/.meta/config.json

@@ -0,0 +1,17 @@
+{
+  "blurb": "Learn about extension-methods by analysing logs.",
+  "authors": [
+    "yzAlvin"
+  ],
+  "files": {
+    "solution": [
+      "LogAnalysis.cs"
+    ],
+    "test": [
+      "LogAnalysisTests.cs"
+    ],
+    "exemplar": [
+      ".meta/Exemplar.cs"
+    ]
+  }
+}

exercises/concept/log-analysis/.meta/design.md

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+# Design
+
+## Goal
+
+The goal of this exercise is to teach the student the Concept of Extension Methods in C#.
+
+## Learning objectives
+
+- Know what extension methods are.
+- Know how to define extension methods on reference and value types
+
+## Out of scope
+
+- Assemblies.
+
+## Concepts
+
+- `extension-methods`: know what extension methods are; know how to define extension methods on reference and value types.
+
+## Prerequisites
+
+- `classes`: know what instance methods are.
+- `namespaces`: know what namespaces are; know how to import namespaces.
+- `collections`: know what collections are.
+
+## Resources to refer to
+
+### Hints
+
+- [Extension methods][extension-methods]: how to define extension methods.
+- [Namespaces][namespaces]: how to define an import namespaces.
+- [Collections][collections]: what a collections is.
+
+### After
+
+- [Extension methods][extension-methods]: how to define extension methods.
+- [Namespaces][namespaces]: how to define an import namespaces.
+- [Collections][collections]: what a collections is.
+
+[extension-methods]: https://docs.microsoft.com/en-us/dotnet/csharp/programming-guide/classes-and-structs/extension-methods
+[namespaces]: https://docs.microsoft.com/en-us/dotnet/csharp/fundamentals/types/namespaces
+[collections]: https://docs.microsoft.com/en-us/dotnet/csharp/programming-guide/concepts/collections

exercises/concept/log-analysis/LogAnalysis.cs

@@ -0,0 +1,24 @@
+using System;
+
+public static class LogAnalysis 
+{
+    public static int WordCount(this string log)
+    {
+        throw new NotImplementedException("Please implement the WordCount() extension method for strings");
+    }
+
+    public static string LogLevel(this string log)
+    {
+        throw new NotImplementedException("Please implement the LogLevel() extension method for strings");
+    }
+
+    public static string LogLine(this string log)
+    {
+        throw new NotImplementedException("Please implement the LogLine() extension method for strings");
+    }
+
+    public static string Truncate(this string log, int maxSize)
+    {
+        throw new NotImplementedException("Please implement the Truncate() extension method for strings");
+    }
+}

exercises/concept/log-analysis/LogAnalysis.csproj

@@ -0,0 +1,14 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>net5.0</TargetFramework>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="16.8.3" />
+    <PackageReference Include="xunit" Version="2.4.1" />
+    <PackageReference Include="xunit.runner.visualstudio" Version="2.4.3" />
+    <PackageReference Include="Exercism.Tests" Version="0.1.0-alpha" />
+  </ItemGroup>
+
+</Project>

exercises/concept/log-analysis/LogAnalysisTests.cs

@@ -0,0 +1,56 @@
+using Xunit;
+using Exercism.Tests;
+using System;
+
+public class LogAnalysisTests
+{
+    [Fact]
+    public void Word_count_of_words_in_log()
+    {
+        Assert.Equal(7, "[Error]: {Line 20} - 'Critical error found'".WordCount());
+    }
+
+    [Fact(Skip = "Remove this Skip property to run this test")]
+    public void Word_count_of_log_with_space_separated_non_alphabet()
+    {
+        Assert.Equal(6, "[Error]: {Line 3} - '; expected'".WordCount());
+    }
+
+    [Fact(Skip = "Remove this Skip property to run this test")]
+    public void Log_level_of_warning_log()
+    {
+        Assert.Equal("Warning", "[Warning]: {Line 11} - 'Trim will be deprecated soon'".LogLevel());
+    }
+
+    [Fact(Skip = "Remove this Skip property to run this test")]
+    public void Log_level_of_error_log()
+    {
+        Assert.Equal("Error", "[Error]: {Line 8} - '; expected'".LogLevel());
+    }
+
+    [Fact(Skip = "Remove this Skip property to run this test")]
+    public void Log_line_of_log_with_single_digit()
+    {
+        Assert.Equal("1", "[Warning]: {Line 1} - 'Trim will be deprecated soon'".LogLine());
+    }
+
+    [Fact(Skip = "Remove this Skip property to run this test")]
+    public void Log_line_of_log_of_log_with_mulitple_digits()
+    {
+        Assert.Equal("111", "[Warning]: {Line 111} - 'Trim will be deprecated soon'".LogLine());
+    }
+
+    [Fact(Skip = "Remove this Skip property to run this test")]
+    public void Truncate_log_does_not_change_log_with_less_than_10_characters()
+    {
+        var log = "[Warning]: {Line 9} - 'The library bogo is deprecated.'";
+        Assert.Equal("[Warning]: {Line 9} - 'The library bogo is deprecated.'", log.Truncate(10));
+    }
+
+    [Fact(Skip = "Remove this Skip property to run this test")]
+    public void Truncate_log_trims_log_with_more_than_10_words()
+    {
+        var log = "[Warning]: {Line 9} - 'The library bogo_sort is deprecated by really_quick_algorithm.'";
+        Assert.Equal("Warning - 9", log.Truncate(10));
+    }
+}