New features in C# 6.0 and 7.0

In this blog post, I will share some of my thoughts on the recent years of development in the .NET world, eventually leading up to the release of C# 6.0 in 2015, and C# 7.0 now in 2017 (it was released 10 days before this blog post was written).

Introduction

First, let's make one thing very clear: Microsoft are not who they used to be. At one time, Microsoft was perceived quite "evil" if you like: a monopoly-oriented company with a very large market share, but with very little technical excellence and a seemingly very narrow-minded way of thinking. It was really Windows-only, IIS-only, and IE-only. Either you accepted the One Microsoft Way to see things, or you were in for problems.

This has clearly changed to the better, and I believe that Satya Nadella is one of the reasons for this. He has had a very positive impact on the company, in my opinion. His decision to really "open up" things have really led to some great things, including:

• The open source release of the .NET Framework (.NET Core), opening up the .NET development to a much larger audience of potential contributors, and also making it cross-platform (Windows, macOS, Linux), making it much more generally useful.
• Windows Subsystem for Linux (WSL), making it possible to run an unmodified Ubuntu on top of Windows 10.

I feel very positive about this, and it has been a part of making me interested in what Microsoft is up to again. After all, I have been using macOS since 2011 now, so for me, the cross-platform part is a rather important aspect of this. I have played around a bit with their latest programmer tools (.NET Core 1.x on macOS and Linux, Visual Studio Code) and thus far, I am very pleased with them.

Anyway, after this long-winded introduction, let me share some of the things I appreciate in C# 6.0 and 7.0

C# 6.0

As noted in the introduction above, C# 6.0 has been out for a while at the time of writing (two years). Still, I haven't used it that much since most of my (professional) work is Ruby-based these days, but these are some of the really nice things I've started using in the C# projects which I still work on.

Expression bodies on method-like members

This is a way to write code which actually, funnily enough, is a bit more like Ruby. Here is the Microsoft-provided example from their wiki page about C# 6:

public void Print() => Console.WriteLine(First + " " + Last);

You can also have multiple lines, and what's not shown in the example above is that if you return a value, you may omit the normal return statement completely (which is very much like Ruby and Rust). Like this, single-line example first:

public static DateTime FromOADate(double days) => new DateTime(1899, 12, 30).AddDays(days);

...and here a much more complex, multi-line example:

private static MethodInfo GetMethodForSubcommand(TypeInfo commandTypeInfo, string subCommand) =>
    commandTypeInfo
      .GetMethods()
      .Where(m => m
        .GetCustomAttributes(typeof(SubCommandAttribute))
        .SingleOrDefault(a => ((SubCommandAttribute)a).Name == subCommand) != null
      ).SingleOrDefault();

It also works for properties (remember that properties is basically just syntactic sugar for methods in C#/.NET). Note that the property syntax here might look a bit unfamiliar; it uses something called "Expression bodies on property-like function members" which is a way to declare a get-only property with a method body.

private DatabaseInserter DatabaseInserter => new DatabaseInserter { ConnectionString = ConnectionString };

It's a small thing, but once you've gotten used to the convenience of "implicit return" (in Ruby), it's really something you miss in languages that lack it.

Null-safe navigation

This is a really, really nice one. The newly added ?-operator means that you navigate to a given property, but only if the object its contained in is non-null, which is a pattern that is very useful in the C# world. So you can write code like this:

public void AddWork()
{
    if (SelectedTrelloCard?.EstimateMissing == true)
    {
        // Do something useful
    }
    else
    {
        // Do something else
    }
}

...instead of this:

public void AddWork()
{
    if (SelectedTrelloCard != null && SelectedTrelloCard.EstimateMissing)
    {
        // Do something useful
    }
    else
    {
        // Do something else
    }
}

Nice, and very convenient. The careful reader will note that the first example uses the dreaded == true syntax. This is usually seen as an anti-pattern in C#, for a regular bool, that is; since the bool is already boolean, you can (and should!) just do if (foo) rather than if (foo == true). But since the expression in this case can be null, the result of that expression (SelectedTrelloCard?.EstimateMissing) isn't really bool but instead bool?, i.e. the nullable version of the bool type. So, in that case you actually have to write == null to make the code compile, since the compiler refuses to make this conversion implicitly.

String interpolation

Again, something which has been present in languages like Ruby and CoffeeScript for years already; it's great that the fine folks at Microsoft are finally adding these great features.

The syntax looks like this:

public override string ToString() => $"{ParentCategory}: {Name}";

Nothing weird in this; the $" at the beginning of the string marks this as a "string that should be interpolated". It means that the result of this ToString() method call will basically be ParentCategory + ": " + Name, it's just a more convenient way to write it. Especially if you have a longer string, it is very useful to just inject a variable or property like that.

The best part of the string interpolation in C# is that all of this happens at compile-time, not like in Ruby and CoffeeScript where it's taking place at runtime. This has the advantage that you can get a really great editing experience, with full IntelliSense and squiggles/compilation errors if you make a typing mistake. Microsoft has here really taken something that is useful in the other camps, and made it even more useful and practical in C#-land! Very nice indeed, it's the kind of thing that makes you want to come back to programming more in C# again.

Alright, enough of the goodness of C# 6.0 and over to the most recently released version, namely 7.0.

C# 7.0

Here I must admit: I don't really know all the features of C# 7.0 by heart yet. It's a very new version of the language, and I've only used a very small subset of the new features. So, I will focus on these here since I can't really advocate features I've never even experienced myself.

Anyhow, here are some of the nice parts. Let's start with Tuples.

Tuples

Tuples are a nice way to group related things together without having to declare an explicit class or struct for them. Consider this example, where I use a Tuple return type:

 public static (TransactionSummary, TransactionSummary) ParseExcelFile()
    {
        var package = new ExcelPackage(new FileInfo("budget.xlsx"));
        var incomesWorksheet = package.Workbook.Worksheets.FindIncomesWorksheet();
        var expensesWorksheet = package.Workbook.Worksheets.FindExpensesWorksheet();

        var incomes = GetTransactionSummary(incomesWorksheet);
        var expenses = GetTransactionSummary(expensesWorksheet);

        return (incomes, expenses);
    }

The parentheses (TransactionSummary, TransactionSummary) in the method signature and the return statement: return (incomes, expenses) is using the new syntax.

Being able to return multiple values from a method - nice, huh? Again, this is something that's been available in other languages (like, Ruby ) for years already, but it's very nice to see it making its way into C# as well.

Tuples are nice, but without the next feature, it wouldn't be as useful. Namely, tuple deconstruction.

Tuple deconstruction

So, you have a parameter which consists of a tuple with multiple values (start and end) below. But how do you use these values?

private static IList<Transaction> GetTransactions(ExcelRange cells, IEnumerable<SubCategory> subCategories, (int, int) start, (int, int) end)
{
    var transactions = new List<Transaction>();

    var (startRow, startColumn) = start;
    var (endRow, endColumn) = end;

    // ...

    return null;
}

The var (startRow, startColumn) = start is the tuple deconstruction. Again, all of this happens at compile time so the var variables will have the proper types, you get compile-time checking if you use these variables incorrectly, etc. Just like you could expect in a statically typed, compiled language like C#.

Alright, that's all of me for this time - hope to see you soon again in some other interesting topic.