Over the past couple of previews, new C# language features have been trickling in, but Preview 4 marks a point where the majority of C# 7.0 are now available.

Here’s a code sample that uses a good number of these features, and that works in Preview 4 today:

class Program
{
    static void Main(string[] args)
    {
        object[] numbers =
            { 0b1, 0b10, new object[] { 0b100, 0b1000 },   // binary literals
             0b1_0000, 0b10_0000 };                        // digit separators
        var (sum, count) = Tally(numbers);                 // deconstruction
        WriteLine($"Sum: {sum}, Count: {count}");
    }
    static (int sum, int count) Tally(object[] values)     // tuple types
    {
        var r = (s: 0, c: 0);                              // tuple literals
        void Add(int s, int c) { r = (r.s + s, r.c + c); } // local functions
        foreach (var v in values)
        {
            switch (v)                                     // switch on any value
            {
                case int i:                                // type patterns
                    Add(i, 1);
                    break;
                case object[] a when a.Length > 0:         // case conditions
                    var t = Tally(a);
                    Add(t.sum, t.count);
                    break;
            }
        }
        return r;
    }
}

For a full write-up about tuples, deconstruction, pattern matching, local functions, and the rest of C# 7.0, head over to the .NET Blog.

Earlier versions of some of these features were shown at Build 2016.

Happy hacking!

Mads Torgersen, C# Language Program Manager @MadsTorgersen Mads leads the design of the C# language. During his 11 years at Microsoft he also contributed to Typescript, Roslyn, Visual Basic, and LINQ. Before that he was a professor at Aarhus University, doing research on programming languages and type systems.