How does grouping data with parentheses work?

Question

I recently came across this:

(int, string) tst = (0, "Test");

The idea behind it seems amazing, before whenever I wanted to map two variables I would use a KeyValuePair. It seems that this is available in .NET Core and not on the regular .NET 4.7.2 which is where I mostly program.

Am I missing something or this is only available on the .NET Core? What is the name of this variable grouping (so I can further research)? Is it the same as creating an object with two variables?

Here is an example:

(int, string) tst = (0, "Test");
var (k, b) = tst;

Console.WriteLine("k: " + k);
Console.WriteLine("b: " + b);

It's a silly question but thank you for the help.

That is a “Value Tuple”, using syntax (type name, tuple creation, and destructuring) added in C#7. — user2864740, Jan 01 '20 at 03:02
Look at tuples: https://learn.microsoft.com/dotnet/api/system.tuple — VillageTech, Jan 01 '20 at 03:02
@VillageTech - the semantics are for [`System.ValueTuple`](https://learn.microsoft.com/en-us/dotnet/api/system.valuetuple?view=netframework-4.8) (the struct), not [`System.Tuple`](https://learn.microsoft.com/dotnet/api/system.tuple) (the class). — Wai Ha Lee, Jan 01 '20 at 03:10

Anu Viswan · Accepted Answer · 2020-01-01T03:39:16.043

You are looking at Tuples in the code in OP. Tuples were available before C# 7.0 too, but the improvements in Tuples (with introduction of ValueTuples) in C# 7.0 meant, one could use semantic names for fields of Tuples as seen in example.

(int, string) tst = (0, "Test");

In the above code, the tuples is unpacked and assigned to tst variable. This is known as decontructing the tuple.

Consider the following code from OP

(int, string) tst = (0, "Test");
var (k, b) = tst;

You could combine this as

var (k, b) =  (0, "Test");

You could use Deconstruct in User Defined Types as well. For example, Consider the following code

public class User
{
    public string FirstName{get;set;}
    public string LastName{get;set;}
    public int Age{get;set;}
}

In order to support Deconstruct in above class, you could add a method as following.

public class User
{
    public string FirstName{get;set;}
    public string LastName{get;set;}
    public int Age{get;set;}

    public void Deconstruct(out string fName,out string lName,out int age)
    {
        fName = FirstName;
        lName = LastName;
        age = Age;
    }
}

The Deconstruct method has now enable us to support Deconstruction in the Class User. You could now write code similar to Tuple Deconstruct. For example,

var user = new User{FirstName = "John", LastName="Doe",Age=50};
var (fName,lName,age) = user;

Fun information: In the “(.., ..) = (.., ..)” case the C# compiler entirely decomposes the operation and does not even create a tuple instance; it’s as efficient as a manual n-variable swap/assignment. — user2864740, Jan 01 '20 at 03:10

How does grouping data with parentheses work?

1 Answers1