Robin blogging about dev stuff

Actually usable tuples in C#

If you, like me, have missed that C# now have support for actually usable tuples then you’re in for a treat.

Previously if you didn’t want to create a DTO class and return that from a function you could use the generic Tuple<T>. And you would write something like this:

static Tuple<int, int, int> Sum(int x, int y)
    return Tuple.Create(x, y, x + y);

This syntax wasn’t really the problem. The real issue was when you used this function:

var tuple = Sum(1, 2);
Console.WriteLine($"The sum of {tuple.Item1} and {tuple.Item2} is {tuple.Item3}");

It is’nt very clear for the reader what Item1, Item2 or Item3 is more than that it is an integer.

Tuples in C# 7

In C# 7 there is a new version of the tuple which makes it usable and that’s both a better looking syntax and the concept of named tuples.

First lets rewrite the Sum fuction with the new syntax:

static (int x, int y, int sum) Sum(int x, int y)
    return (x, y, x + y);

We can get rid of the Tuple<T> type completly and replace it with parentheses and the types along with the names. You will get suggestions in autocomplete for these names.

When you want to use this function the syntax is now more clear with the names from the tuple:

var result = Sum(2, 3);
Console.WriteLine($"The sum of {result.x} and {result.y} is {result.sum}");


Along with the new syntax for tuples there is also syntax for deconstruction. This means that if we rewrite our Sum function to look like this:

static (int, int, int) Sum(int x, int y)
    return (x, y, x + y);

Now that we aren’t returning the names for each value in the tuple we can use deconstruction to assing names:

var (x, y, sum) = Sum(1, 2);
Console.WriteLine($"The sum of {x} and {y} is {sum}");

Deconstruction, for now, only works for tuples out of the box. If you want to use deconstruction for your classes you can implement a Deconstruct function on your class:

class Person
    public string Firstname { get; set; }
    public string Lastname { get; set; }

    public void Deconstruct(out string firstname, out string lastname)
        firstname = Firstname;
        lastname = Lastname;

You can then use deconstuction like this:

var (firstname, lastname) = new Person { Firstname = "Robin", Lastname = "Ridderholt" };
Console.WriteLine($"{firstname} {lastname}");


So there you go. This might seem like small changes but I think it’s a nice change. It will get rid of many small classes that I write whenever I need to return more than one value from a function, and along with deconstruction we get a clean syntax.

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