What's my version again?

( it's 5.0 )

(the one with async/await)

C# 6

is out this year

• out with Visual Studio 2015
• new Roslyn compiler
• await in try/finally
• lots of property syntax sugar
• expression bodies
• null conditional operator ?.
• lots more

What about 7.0?

C# is developed in the open

• C# 7 design meeting notes are on Github.
• They're organized, thorough, and accessible.
• This talk comes entirely from their notes.

Not now

• C# 7 is a work in progress. A lot will change.
• Let's look anyway.
• github.com/dotnet/roslyn/issues/2136

• To find this later, google "C# 7 features."

Tuples

Real language support, not just System.Tuple

public (double meanAge, int oldest) GetAgeStats(IEnumerable<Person> people)
{
    var mean = people.Average(x => x.Age);
    var max = people.Max(x => x.Age);
    var result = (meanAge: mean, oldest: max);
    return result;
}

(var mean, var oldest) = GetAgeStats(people);

Non-nullable references

Dog - regular reference we have today

Dog! - a reference which cannot be null

Dog? - a reference which might be null

• Compiler won't let you dereference anything from a Dog? unless you do a null check first. It's opting into safety.
• Use Dog! everywhere you can, to preserve nullability information.

Deterministic disposal

• Adds the notion of a destructible type.
• Alternative to IDisposable or a finalizer.
• Ensures an object's destructor is called exactly when the variable goes out of scope. No using() or waiting for GC.
• Compiler enforces you can't make copies of the variable or stash them away.

public destructible struct ImageResource
{
    ...
    ~Cleanup() { ... }
}

Record types

• Special class made with shorthand notation
• Compiler generates a full class with private readonly backing fields and public properties that only have getters.
• You can add more to your class declaration to override defaults, like adding setters.

public class Celsius(double Temperature);
public class Fahrenheit(double Temperature);

public class Cartesian(double X, double Y);
public class Polar(double r: Radius, double phi: Angle);

Record types

• Can omit "new" when instantiating.
• "is" operator now overridable.

public class Fahrenheit(double Temperature)
{
    public bool operator is(Celsius c) { ... }
}

var someTemp = Fahrenheit(212.0); //don't need new
if(someTemp is Celsius(100.0))
{
    //someTemp is boiling
}

Pattern matching

• New ways to use "switch" and "is" keywords

var v = foo as Video;
if (v != null) {
    //code using v
}

becomes

if (foo is Video v) {
    //code using v
}
//v doesn't exist

Pattern matching

• New ways to use "switch" and "is" keywords

abstract class Shape;
class Square(double Width, double Height) : Shape;
class Circle(double Radius) : Shape;

public double GetArea(Shape shape) {
  switch(shape) {
    case Square(1.0, 1.0): return 1.0;
    case Square s: return s.Width * s.Height;
    case Circle c: return Math.PI * c.Radius * c.Radius;
  }
}

All the small things

• Most of this will change, but it gives an idea of the direction of the language.
• Pattern matching, Records, Tuples, and much more are features taken directly from F# and other functional programming languages.
• Many C# features have similar origins, such as generics, lambdas, LINQ, etc.
• Deterministic destructors is based on "linear types" which is new ground for PLs. Only Rust has this in practice, and 1.0 just came out.

Feeling this

• I love C#, and I think it keeps getting better.
• Open development
• Open source
• Multi-platform
• Not afraid to push the boundries a bit
• If you don't feel the same, that's cool too.
• Life is short, be kind and enjoy colors.

(sorry if you're colorblind)