What’s new in C# 7.0

Project roslyn is bringing good news. A lot of new features are coming up and you can check the status on GitHub (not all features are guaranteed to make it in time).

I created a GitHub project – brunolm/csharp-features to show what is coming and how to use it.

csharp new features

Binary Literals

Now you can write binary codes directly:

var bin = 0b1010;


Now it is easier to see if you need more or less zeros.

var bin = 0b00001010_10010011;
var num = 8_000_000_000;
var hex = 0xAB_CD_EF;

Throw Exception Inline

Now you can throw an exception in a ternary operator.

var x = true ? throw new ArgumentNullException() : false;

Catch When

You can catch errors only if some condition is met.

catch (Exception ex) when (ex.Message.EndsWith("!"))

Expression Bodied Everything

Now you can use expression bodied in “everything”.

class Person
    private IList names = new List();

    public Person(string name) => names.Add(name);
    ~Person() => names.Clear();

    public int Total
        get => names.Count;

Local Functions

You can now declare functions inside your methods.

public void Calc()
    int fib()
        return 1;

    int x = fib();

Out Vars

You can do this in a one-line now.

int.TryParse("1337", out int n)

You can use var

int.TryParse("1337", out var n)

If there are multiple out parameters:

public void GetCoords(out int x, out int y, out int z)

You can discard what you don’t want using out _:

GetCoords(out int x, out _, out _);

See discards and wildcards work.

Pattern Matching – IS

You can check if a variable is something and create another one in that type immediately:

IShape o = new Circle();
if (o is Circle c) /* something with variable c */

Pattern Matching – Switch

Switches can now combine is and when. There is also a special case null that will catch (even with the default before it) when shape is null.

public void Switch()
    IShape shape = new Square();

    switch (shape)
        case Circle c when (c.Length == 5):
        case Circle c:
        case Square s:
        case null: // special case, does not fall in default

Ref Returns

It allows you to return the address of the value and modify the value.

public void Usage()
    int[] arr = { 5, 4, 3, 2, 1 };

    ref int Find(int n)
        for (int i = 0; i < arr.Length; ++i)
            if (arr[i] == n)
                return ref arr[i];

        throw new System.Exception();

    ref int pos = ref Find(5);
    pos = 100;

    System.Console.WriteLine(arr); // { 100, 4, 3, 2, 1 };


To use tuples today you need to install a package:

# Core
dotnet add package System.ValueTuple

# Nuget
Install-Package "System.ValueTuple" -IncludePrerelease

Allows you to return more than one value at once. Usually you would need to create a class to return multiple things, now you can:

public (int, int) GetCoords()
    return (1, 2);

var (x, y) = GetCoords();
(var w, var z) = GetCoords();

If the return types are not named and you attempt to get all values in a single var, it will return an object with Item1, Item2

var all = GetCoords();
// all.Item1
// all.Item2

You can change the method signature to return an object with named properties

public (int x, int y) GetCoordsNamed() {}

var obj = GetCoordsNamed();
// obj.x
// obj.y

And there are more planned but apparently not yet available, like non-nullable vars string! notNullString.

I’m quite happy to see these new features, allowing C# to be more flexible, reducing the amount of code needed to do things. I hope you are enjoying too 🙂


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