ICYMI C# 8 New Features: Simplify Array Access and Range Code

This is part 5 in a series of articles.

One of the new features that C# 8 introduced was the ability to work more simply with arrays and items within arrays.

Take the following code that uses various ways to manipulate an array of strings:

string[] letters = { "A", "B", "C", "D", "E", "F" };

string firstLetter = letters[0];
string secondLetter = letters[1];
string lastLetter = letters[letters.Length - 1];
string penultimateLetter = letters[letters.Length - 2];

string[] middleTwoLetters = letters.Skip(2)
                                   .Take(2)
                                   .ToArray();

string[] everythingExceptFirstAndLast = letters.Skip(1)
                                               .Take(letters.Length - 2)
                                               .ToArray();

It’s pretty easy to get the first element in an array [0] and the last item [letters.Length - 1] but when we get to getting ranges (like the middle 2 letters) or 2 from the end things get a little more complicated.

C# 8 introduced a new shorter syntax for dealing with indices and ranges. The preceding code could be re-rewritten in C# 8 as follows:

string[] letters = { "A", "B", "C", "D", "E", "F" };

string firstLetter = letters[0];
string secondLetter = letters[1];
string lastLetter = letters[^1];
string penultimateLetter = letters[^2];

string[] middleTwoLetters = letters[2..4];

string[] everythingExceptFirstAndLast = letters[1..^1];

There’s a few different things going on in the C#8 version.

First of all, C# 8 gives us the new index from end operator ^. This essentially gives us an element by starting at the end and counting back. One thing to note here is that the index ^0 is not the last element, rather the length of the array (remember in C# arrays are zero-based). The last element is actually at ^1. If you try and access an element using [^0] you’ll get an IndexOutOfRangeException just as you would if you wrote [letters.length].

In additional to the index from end operator, C# 8 also introduced the range operator .. – this allows you to specify a range of elements. For example in the code, the range [2..4] gives us the middle 2 letters C & D – or more specifically, it gives us the range of elements starting at 2 and ending at 4. Why 4 though? When using the range operator, the first index is inclusive but the last index is exclusive. So [2..4] really means “2 to 3 inclusive”.

To make the new indexing feature work, there is a new struct called Index. And to make ranges work there is a new struct called Range.

For example, you can create and pass Range instances around:

Range middleTwo = new Range(2, 4);
string[] middleTwoLetters = letters[middleTwo];

You can also use the index from end operator in a range, for example to get the last 3 letters:

string[] lastThreeLetters = letters[^3..^0]; // D E F

Notice in this code we are using ^0 (and get no exception) to specify the end because the end of a range is exclusive.

As well as arrays you can also use these techniques with other types which you can read more about  in the Microsoft documentation e.g. the MS docs state: “For example, the following .NET types support both indices and ranges: String, Span<T>, and ReadOnlySpan<T>. The List<T> supports indices but doesn't support ranges.” And also from the docs: “Any type that provides an indexer with an Index or Range parameter explicitly supports indices or ranges respectively. An indexer that takes a single Range parameter may return a different sequence type, such as System.Span<T>.”…and… “A type is countable if it has a property named Length or Count with an accessible getter and a return type of int. A countable type that doesn't explicitly support indices or ranges may provide an implicit support for them. For more information, see the Implicit Index support and Implicit Range support sections of the feature proposal note. Ranges using implicit range support return the same sequence type as the source sequence.”

If you want to fill in the gaps in your C# knowledge be sure to check out my C# Tips and Traps training course from Pluralsight – get started with a free trial.

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ICYMI C# 8 New Features: Nested Switch Expressions

This is part 4 in a series of articles.

In this series we’ve already covered switch expressions and one little-known feature is the ability to nest switch expressions.

Suppose we have the following 3 classes:

class SavingsAccount
{
    public decimal Balance { get; set; }
}

class HomeLoanAccount
{
    public int MonthsRemaining { get; set; }
}

class ChequingAccount
{
    public decimal NumberOfTimesOverdrawn { get; set; }
    public int NumberOfAccountHolders { get; set; }
}

(Notice that none of the preceding classes are linked by inheritance.)

Suppose we wanted to run a gift card promotional mailing depending on what accounts customers had. We can use pattern matching on the type of object in a switch expression:

decimal CalculatePromotionalGiftCardValue(object account) => account switch
{
    SavingsAccount sa when (sa.Balance > 10_000) => 100,
    SavingsAccount _ => 0, // all other savings accounts

    HomeLoanAccount hla when (hla.MonthsRemaining < 12) => 20,
    HomeLoanAccount _ => 0, // all other home loan accounts

    ChequingAccount ca when (ca.NumberOfTimesOverdrawn == 0 && ca.NumberOfAccountHolders == 1) => 20,
    ChequingAccount ca when (ca.NumberOfTimesOverdrawn == 0 && ca.NumberOfAccountHolders == 2) => 40,
    ChequingAccount ca when (ca.NumberOfTimesOverdrawn == 0 && ca.NumberOfAccountHolders == 3) => 50,
    ChequingAccount _ => 0, // all other chequing accounts

    { } => throw new ArgumentException("Unknown account type", paramName: nameof(account)), // all other non-null object types
    null => throw new ArgumentNullException(nameof(account))
};

Notice in the preceding expression-bodied method containing a switch expression (that’s a mouthful!), that there is a bit of repetition in the ChequingAccount section with the ca.NumberOfTimesOverdrawn == 0 code being repeated. We can replace this section with a nested switch expression:

decimal CalculatePromotionalGiftCardValueNested(object account) => account switch
{
    SavingsAccount sa when (sa.Balance > 10_000) => 100,
    SavingsAccount _ => 0,

    HomeLoanAccount hla when (hla.MonthsRemaining < 12) => 20,
    HomeLoanAccount _ => 0,

    ChequingAccount ca when (ca.NumberOfTimesOverdrawn == 0) => ca.NumberOfAccountHolders switch
    {
        1 => 20,
        2 => 40,
        3 => 50,
        _ => 0
    },
    ChequingAccount _ => 0,

    { } => throw new ArgumentException("Unknown account type", paramName: nameof(account)),
    null => throw new ArgumentNullException(nameof(account))
};

If you want to fill in the gaps in your C# knowledge be sure to check out my C# Tips and Traps training course from Pluralsight – get started with a free trial.

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ICYMI C# 8 New Features: Simplify If Statements with Property Pattern Matching

This is part 3 in a series of articles.

In the first part of this series we looked at switch expressions.

When making use of switch expressions, C# 8 also introduced the concept of property pattern matching. This enables you to match on one or more items of an object and helps to simplify multiple if..else if statements into a more concise form.

For example, suppose we had a CustomerOrder:

class CustomerOrder
{
    public string State { get; set; }
    public bool IsVipMember { get; set; }
    // etc.
}

And we created an instance of this:

var order1 = new CustomerOrder
{
    State = "WA",
    IsVipMember = false
};

Now say we wanted to calculate a delivery cost based on what State the order is being delivered to. If the customer is a VIP member then the delivery fee may be waived depending on what the State is. We could write this using if…else if:

if (order1.State == "WA" && order1.IsVipMember)
{
    deliveryCost = 0M;
}
else if (order1.State == "WA" && !order1.IsVipMember)
{
    deliveryCost = 2.3M;
}
else if (order1.State == "NT" && !order1.IsVipMember)
{
    deliveryCost = 4.1M;
}
else
{
    deliveryCost = 5M;
}

The preceding code will get bigger and harder to read the more states we add.

An alternative could be to use a switch statement to try and simplify this:

decimal deliveryCost;

switch (order1.State, order1.IsVipMember)
{
    case ("WA", true):
        deliveryCost = 0M;
            break;
    case ("WA", false):
        deliveryCost = 2.3M;
        break;
    case ("NT", false):
        deliveryCost = 4.1M;
        break;
    default:
        deliveryCost = 5M;
        break;
}

In the preceding code there is still a bit of “ceremony” with all the case blocks.

We could instead use a switch expression that makes use of property pattern matching:

deliveryCost = order1 switch
{
    { State: "WA", IsVipMember: true } => 0M,
    { State: "WA", IsVipMember: false } => 2.3M,
    { State: "NT", IsVipMember: false } => 4.1M,
    _ => 5M
};

Notice how the preceding code is a lot more succinct, and it’s easy to see all the cases and combinations.

What if for some States, the VIP status was not relevant for calculating delivery cost?

Suppose that the state “QE” always had a high delivery cost that never got reduced even for VIPs:

deliveryCost = order1 switch
{
    { State: "WA", IsVipMember: true } => 0M,
    { State: "WA", IsVipMember: false } => 2.3M,
    { State: "NT", IsVipMember: false } => 4.1M,
    { State: "QE"} => 99.99M,
    _ => 5M
};

In the preceding code, if the State is “QE” then the delivery cost will be 99.99. Also notice the use of the discard _ that says “for all other combinations not listed above set the delivery cost to 5”.

If you want to fill in the gaps in your C# knowledge be sure to check out my C# Tips and Traps training course from Pluralsight – get started with a free trial.

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ICYMI C# 8 New Features: Write Less Code with Using Declarations

This is part 2 in a series of articles.

One nice little enhancement introduced in C# 8 helps to simplify code that uses disposable objects.

For example consider the following:

class MyDisposableClass : IDisposable
{
    public void Dispose()
    {            
        Console.WriteLine("Disposing");
    }

    public void Run() 
    {
        Console.WriteLine("Running");
    }
}

Prior to C# 8, if you wanted to use a disposable object (something that implements IDisposable) then you would usually use a using block as follows:

private static void Process()
{
    using (var x = new MyDisposableClass())
    {
        x.Run();
    }
}

At the end of the using block, the Dispose() method is called automatically.

With C# 8, instead of the using block, you can instead use a using declaration:

private static void Process()
{
    using var x = new MyDisposableClass();

    x.Run();
}

Notice in the preceding code, with a using declaration there is no need for the additional {}. When using a using declaration, the Dispose() method is called automatically at the end of the Process() method. Just as with the using block approach, if an exception occurs within the Process() method then Dispose() will still be called.

Using declarations help to keep code less cluttered because you have fewer braces {} and one level less of indenting.

If you have multiple usings, for example:

private static void Process()
{
    using (var x = new MyDisposableClass())
    using (var y = new MyDisposableClass())
    using (var z = new MyDisposableClass())
    {
        x.Run();
        y.Run();
        z.Run();
    }
}

You can rewrite this in C# 8 as follows:

private static void Process()
{
    using var x = new MyDisposableClass();
    using var y = new MyDisposableClass();
    using var z = new MyDisposableClass();

    x.Run();
    y.Run();
    z.Run();
}

If you want to fill in the gaps in your C# knowledge be sure to check out my C# Tips and Traps training course from Pluralsight – get started with a free trial.

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ICYMI C# 8 New Features: Switch Expressions

In the first part of this series on what was introduced in C# 8, we’re going to take a look at switch expressions.

Switch expressions allow you to write fewer lines of code when making use of switch statements. This is useful if you have a switch statement that sets/returns a value based on the input.

Prior to C# 8, the following code could be used to convert an int to its string equivalent:

string word;
switch (number)
{
    case 1:
        word = "one";
        break;
    case 2:
        word = "two";
        break;
    case 3:
        word = "three";
        break;
    default:
        throw new ArgumentOutOfRangeException(nameof(number));                    
}

In the preceding code if the input int number is not 1,2, or 3 an exception is thrown, otherwise the variable word is set to the string representation “one”, “two”, or “three”.

From C# 8 we could instead use a switch expression. A switch expression returns a value, this means we can return the string into the word variable as follows:

string word = number switch
{
    1 => "one",
    2 => "two",
    3 => "three",
    _ => throw new ArgumentOutOfRangeException(nameof(number))
};

Compare this version with first version and you can see we have a lot less code, we don’t have all the repetitive case and breaks.

Also notice that the default block has been replaced with an expression that throws the exception. Also notice that the code makes use of a discard _ as we don’t care about the value. (Discards are “placeholder variables that are intentionally unused in application code” (MS)).

If you want to fill in the gaps in your C# knowledge be sure to check out my C# Tips and Traps training course from Pluralsight – get started with a free trial.

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New Pluralsight Course: Feature Flag Fundamentals with Microsoft Feature Management

My latest Pluralsight video training course was just published just in time for some holiday season learning! :)

From the description: “Releasing software to production can be hard, risky, and time-consuming, especially if there is a problem and you need to roll back the deployment. In this course, Feature Flags Fundamentals and Microsoft Feature Management, you’ll gain the ability to effectively and efficiently manage the development and deployment of features. First, you’ll explore how to configure and use feature flags in code. Next, you’ll discover how to control features and HTML rendering using Microsoft feature flags in an ASP.NET Core app. Finally, you’ll learn how to customize Microsoft Feature Management and even manage features from Azure. When you’re finished with this course, you’ll have the skills and knowledge of Microsoft Feature Management needed to effectively deploy and manage features in production.”

You can read more about the course over on the official course homepage. Or start watching with a free trial today.

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Approval Tests: Assert With Human Intelligence

In the previous article I described how the Approval Tests library can help reduce the amount of assert code that needs to be written. The second benefit of using Approval Tests is the ability to use innate human intelligence to decide if the result of the test is correct.

Imagine a scenario where you need to assert that a text-to-speech generator has generated the correct output. In this example the output could be a byte array representing a .WAV or .MP3 sound file. How would you write traditional asserts to test this output?

As another example, suppose you had to test code that applied a creative filter to an input photograph, this could be some sort of “make skin tones look nice” filter, the output in this case would be a modified image file. How would you assert that the output photo looked “nice”?

In cases like these using traditional asserts may be impossible or very time consuming to implement, there is no Assert.Speech(…) or Assert.LooksNice(…).

This is where the Approval Tests library offers great benefits. You could simply write Approvals.Verify(speechWavBytes); or Approvals.Verify(processedImageBytes); In the case of the sound file you could listen to it and decide if it sounds correct. In the case of the processed photo, you could look at it on screen and use human intelligence to decide if it “looks nice”.

Once you are happy you can approve the results and then in future tests runs if the output accidentally changes due to a bug the tests will fail.

If you want to see Approval Tests in action and learn more about how they can make your testing life easier check out my Approval Tests for .NET Pluralsight course which you can currently start watching for free today with a Pluralsight free trial.

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Approval Tests: Write Tests More Quickly

Sometimes assert code in tests gets big and messy and complicated when the output we’re testing is complex.

Approval Tests is a library that can help simplify assert code. The library has other benefits/use cases which I’ll cover in future posts such as using human intelligence to judge if the output is correct; providing a safety net when refactoring legacy code that has no tests; and even testing view rendering.

In the following test code, notice the assert phase:

[Fact]
public void TraditionalAsserts()
{
    var lines = new List<string>
    {
        "Widget sales: 42",
        "Losses: 99",
        "Coffee overheads: 9,999,999"
    };

    var sut = new ReportGenerator(title: "Annual Report",
                                    footer: "Copyright 2020",
                                    lines);

    string report = sut.Generate();

    // Notice the complexity of the asserts below
    Assert.Equal("Annual Report", report.Split(Environment.NewLine)[0]);
    Assert.Equal("Widget sales: 42", report.Split(Environment.NewLine)[2]);
    Assert.Equal("Losses: 99", report.Split(Environment.NewLine)[3]);
    Assert.Equal("Coffee overheads: 9,999,999", report.Split(Environment.NewLine)[4]);
    Assert.Equal("Total lines: 3", report.Split(Environment.NewLine)[6]);
    Assert.Equal("Copyright 2020", report.Split(Environment.NewLine)[8]);
            

    // We could also have just asserted using a long expected string rather than individual line asserts
}

And for reference the ReportGenerator class looks like the following:

public class ReportGenerator
{
    public string Title { get; }
    public List<string> Lines { get; }
    public string Footer { get; }

    public ReportGenerator(string title, string footer, List<string> lines)
    {
        Title = title;
        Footer = footer;
        Lines = lines;
    }

    public string Generate()
    {
        var report = new StringBuilder();

        report.AppendLine(Title);
        report.AppendLine();

        foreach (var line in Lines)
        {
            report.AppendLine(line);
        }


        report.AppendLine();
        report.AppendLine($"Total lines: {Lines.Count}");

        report.AppendLine();
        report.AppendLine(Footer);

        return report.ToString();
    }
}

So in the test there are 6 lines of assert code:

Assert.Equal("Annual Report", report.Split(Environment.NewLine)[0]);
Assert.Equal("Widget sales: 42", report.Split(Environment.NewLine)[2]);
Assert.Equal("Losses: 99", report.Split(Environment.NewLine)[3]);
Assert.Equal("Coffee overheads: 9,999,999", report.Split(Environment.NewLine)[4]);
Assert.Equal("Total lines: 3", report.Split(Environment.NewLine)[6]);
Assert.Equal("Copyright 2020", report.Split(Environment.NewLine)[8]);

If the output was more complex or bigger (for example 100’s or 1000’s of lines of text) then the assert code would get even more messy and harder to maintain. Or what if the output was some binary representation such as an array of bytes representing a generated image or text to speech sound file?

It’s in these cases when dealing with complex output that Approval Tests can help to simplify the assert code as shown in the following test:

[Fact]
[UseReporter(typeof(DiffReporter))]
public void ApprovalTestsVersion()
{
    var lines = new List<string>
    {
        "Widget sales: 42",
        "Losses: 99",
        "Coffee overheads: 9,999,999"
    };

    var sut = new ReportGenerator(title: "Annual Report",
                                    footer: "Copyright 2020",
                                    lines);

    string report = sut.Generate();

    Approvals.Verify(report);
}

Notice in the preceding code the line: Approvals.Verify(report); This line calls Approval Tests and will create a new  “received” .txt file in the test project. You can examine this text file and if it is correct rename it to be an “approved” file. When the test runs in the future, Approval Tests will use the approved file (which should be added to source control) and if the generated report is the same then the test will pass, otherwise the test will fail and a new received file will be output. The [UseReporter] attribute lets you specify how to visualize approval failures, in this example by using a diff tool, and there’s a number of other reporters that come out of the box that you can use.

If you want to see Approval Tests in action and learn more about how they can make your testing life easier check out my Approval Tests for .NET Pluralsight course which you can currently start watching for free today with a Pluralsight free trial.

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Simplify and Reduce Test Code with AutoFixture

AutoFixture is a library that you can use alongside your testing framework to reduce the amount of boilerplate test code you need to write and thus improve your productivity.

At its core, AutoFixture helps you setup your tests by generating anonymous test data for you. This anonymous test data can be used to fulfil non-important boilerplate test data; this is test data that is required for the test to execute but whose value is unimportant.

Take the follow abbreviated test:

[Fact]
public void ManualCreation()
{
    // arrange

    Customer customer = new Customer()
    {
        CustomerName = "Amrit"
    };

    Order order = new Order(customer)
    {
        Id = 42,
        OrderDate = DateTime.Now,
        Items =
                      {
                          new OrderItem
                          {
                              ProductName = "Rubber ducks",
                              Quantity = 2
                          }
                      }
    };


    // act and assert phases...
}

Suppose the previous test code was only creating an Order (with associated Customer) just to fulfil some dependency and the actual Customer and OrderItems did not matter. In this case we could use AutoFixture to generate them for us.

AutoFixture can be installed via NuGet and once installed allows a Fixture instance to be instantiated. This Fixture object can then be used to generate anonymous test data and greatly simplify the arrange phase, as the following test shows:

[Fact]
public void AutoCreation()
{
    // arrange

    var fixture = new Fixture();

    Order order = fixture.Create<Order>();

    // act and assert phases...
}

If we were to debug this test we’d see the following values:

AutoFixture anonymous test data generation for complex object graphs

Notice in the preceding screenshot that AutoFixture has created the object graph for us, including the Customer and 3 OrderItem instances.

There’s a lot more to AutoFixture than just this simple example, for example you can combine with the AutoFixture.Xunit2 package to further reduce code:

[Theory, AutoData]
public void SubtractWhenZeroTest(int aPositiveNumber, Calculator sut)
{
    // Act
    sut.Subtract(aPositiveNumber);

    // Assert
    Assert.True(sut.Value < 0);
}

If you want to learn more about how AutoFixture can improve your productivity check out the docs or start watching for free  my AutoFixture Pluralsight course with a free trial:

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Running xUnit.net Tests on Specific Threads for WPF and Other UI Tests

Sometimes when you write a test with xUnit.net (or other testing frameworks) you may run into problems if UI technologies are involved. This usually relates to the fact that the test must execute using a specific threading model such as single-threaded apartment (STA).

For example suppose you had a WPF app that you wanted to add tests for.

The XAML looks like:

<Window x:Class="WpfApp1.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:WpfApp1"
        mc:Ignorable="d"
        Title="MainWindow" Height="450" Width="800">
    <Grid>
        <TextBlock FontSize="42" Text="{Binding Path=Greeting}" />
    </Grid>
</Window>

And the simple quick and dirty view model class looks like:

namespace WpfApp1
{
    public class MainWindowViewModel
    {
        public string Greeting { get; set; }
    }
}

And  in the MainWindow constructor we set the data context:

public MainWindow()
{
    InitializeComponent();

    var vm = new MainWindowViewModel { Greeting = "Hi there!" };
    DataContext = vm;
}

(This is a very simple demo code with no change notifications etc.)

If you wanted to write an xUnit.net test that instantiates an instance of MainWindow, such as:

[Fact]
[UseReporter(typeof(DiffReporter))]
public void RenderWithViewModel()
{
    var sut = new MainWindow();
    var vm = new MainWindowViewModel { Greeting = "Good day!" };
    sut.DataContext = vm;

    // Test rendering, e.g. using Approval Tests
    WpfApprovals.Verify(sut);
}

If you run this, the test will fail with: System.InvalidOperationException : The calling thread must be STA, because many UI components require this.

Note: this test is using Approval Tests (e.g. [UseReporter(typeof(DiffReporter))]) to render the UI into an image file for approval, you can learn more about Approval Tests with my Pluralsight course. Approval Tests is no related to the threading model requirements.

To enable this test to run you need to instruct xUnit to run the test using an apartment model process (“STA thread”).

Luckily Andrew Arnott has done all the hard work for us and created some custom xUnit.net attributes that allow us to specify what thread/synchronization context to use for a test.

Once the Xunit.StaFact NuGet package has been installed into the test project you can replace the standard [Fact] attribute with [StaFact]. The test will now execute without error:

using ApprovalTests.Reporters;
using ApprovalTests.Wpf;
using Xunit;

namespace WpfApp1.Tests
{
    public class MainWindowShould
    {
        [StaFact]
        [UseReporter(typeof(DiffReporter))]
        public void RenderWithViewModel()
        {
            var sut = new MainWindow();
            var vm = new MainWindowViewModel { Greeting = "Good day!" };
            sut.DataContext = vm;

            // Test rendering, e.g. using Approval Tests
            WpfApprovals.Verify(sut);
        }
    }
}

There are also a number of other attributes such as [WinFormsFact] for use with Windows Forms apps, check out the entire list of attributes in the docs.

If you use this library make sure to say a thankyou to Andrew on Twitter  :)

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