Tuples — Tuple, ValueTuple in C# — A Summary

This is just a summary of tuple because my notes seem to be all over the place.

What is a Tuple?

Tuples are not the most organized way to handle data, but sometimes they can be very useful. For example, you have a method and you want it to return a value and a message. You could create a class with 2 properties, one for the value and one for the message, but it may seem like too much trouble for just 2 little values. That’s when a Tuple is helpful.

Differences Between ValueTuple and Tuple

There are 2 types of Tuple types in C#, System.Tuple and System.ValueTuple.

System.Tuple => Reference, members are properties, read-only. This means they cannot be changed once they have been created.

System.ValueTuple = > value, members are fields, not read only.

Very simple Tuple of both types:

So what’s the difference?

Tuple types, being reference, are harder on the memory heap and memory allocation, so ValueTuple will give you better performance.

Another way to create the Tuple and ValueTuple is with the Create keyword:

var intTup = System.Tuple.Create<Int32>(100);
var intTupVal = System.ValueTuple.Create<Int32>(200);

For the ValueTuple there is this additional way of creating a new one:

(int, int, int) tup1 = (100,200, 300);
var tup2 = (400,500,600);

//to see the type:
Console.WriteLine(tup2.GetType()); 
//System.ValueTuple`3[System.Int32,System.Int32,System.Int32]

Also, to access the elements of a Tuple or ValueTuple, we have to go Item1, Item2 etc, which is confusing. But with ValueTuple types we can name the elements:

(int first, int second , int third) tup1 = (100,200, 300);
 Console.WriteLine(tup1.first);//100

var tup2 = (first:100, second:200, third:300);
Console.WriteLine(tup2.second); //200

Trying to create a ValueTuple this way if it only has 1 value is not going to compile. It works OK with the other ways to create it (already mentioned).

ValueTuple types can hold more elements than Tuple types. If you have a Tuple, you can convert it to ValueTuple with ToValueTuple.

Nested Tuple

Because Tuple types are limited as far as number of elements, we may need to have a Tuple instead of another Tuple so we can pass everything we need.

var numbers = Tuple.Create(1, 2, 3, 4, 5, 6, 7, Tuple.Create(8, 9, 10, 11, 12));
Console.WriteLine(numbers.Item1); //1
Console.WriteLine(numbers.Rest.Item1); //(8, 9, 10, 11, 12)
Console.WriteLine(numbers.Rest.Item1.Item1);   //8

Comparing ValueTuple, Tuple Types

With ValueTuple types, even if we are giving different names to the elements, what gets compared is the values.

(int x, int y) valtup1 = (3,4);
(int i, int j) valtup2 = (3,4);
       
Console.Write(valtup1 == valtup2);//True

However, for the reference type Tuple:

Tuple<int,int> tup1 = new Tuple<int, int>(3,4);
Tuple<int,int> tup2 = new Tuple<int, int>(3,4);
       
Console.Write(tup1 == tup2);// False

Returning a ValueTuple in a method

Besides returning a type ValueTuple, we can also indicate what names the elements should have.

 public static (int, int) GetAValueTuple(){
   return (first:20, second:30);
 }

 var v = GetAValueTuple();
 Console.WriteLine(v);
 //Console.WriteLine(v.first); will not find first

 (int x, int y) w = GetAValueTuple();
 Console.WriteLine(w);
 Console.WriteLine(w.x); //will not find first but x is 20

 //BUT, if we name the return and the return type!
public static (int first, int second) GetAValueTuple(){
  return (first:20, second:30);
}
var v = GetAValueTuple();
Console.WriteLine(v.first);//20

//We can also do 
(int x, int y) = GetAValueTuple();
Console.WriteLine(x);//20
Console.WriteLine(y);//30

Getting a list of Tuples from a list of Tuples

using System;
using System.Collections.Generic;
using System.Linq;
     
public class Program
{
 public static void Main()
 { 
  List<Tuple<int,int>> mainList = new List<Tuple<int,int>>();
  mainList.Add(new Tuple<int,int>(1,2));
  mainList.Add(new Tuple<int,int>(2,3));
  mainList.Add(new Tuple<int,int>(3,4));
  
  List<Tuple<int,string>> sublist = mainList.Select(row => new Tuple<int, string>(row.Item1,"hello")).ToList();  
 } 
}

Summary of Ways to do Tuples

But first, notice this. You have a declared twice, and you will get a compile error.

public static void Main()
 { 
  (string a, int b) = ("hello", 3); 
  Console.WriteLine(a);//hello
  
  string a; //COMPILE ERROR
  int b;
  (a,b) = ("hello", 3); 
  Console.WriteLine(b);
 } 

Now for the examples:

using System;
     
public class Program
{
 public static void Main()
 { 
  (string a, int b) = ("hello", 3); 
  Console.WriteLine(a);//hello    
 } 
}

using System;
     
public class Program
{
 public static void Main()
 { 
  string a;
  int b;
  (a,b) = ("hello", 3); 
  Console.WriteLine(b);//3
  
 } 
}

using System;
     
public class Program
{
 public static void Main()
 { 
  (var a, var b) = ("hello", 3);
  Console.WriteLine(a);//hello
 } 
}

using System;
     
public class Program
{
 public static void Main()
 { 
  var (a, b) = ("hello", 3);
  Console.WriteLine(a);//hello
 } 
}

using System;
     
public class Program
{
 public static void Main()
 { 
  (string a, int b) myVar = ("hello", 3);
  Console.WriteLine(myVar.a);//hello
 } 
}

using System;
     
public class Program
{
 public static void Main()
 { 
  var myVar =  (theString:"hello", theInt:3);
    Console.WriteLine(myVar.theString);//hello
  Console.WriteLine(myVar.Item1);//hello
 } 
}

using System;
     
public class Program
{
 public static void Main()
 { 
  var myVar =  ("hello", 3);
  Console.WriteLine(myVar.Item1);//hello
 } 
}

using System;
     
public class Program
{
 public static void Main()
 { 
  //hi will be ignored because of the _
  (string a, _, int c) = ("hello", "hi", 3);
    Console.WriteLine(a);//hello
  Console.WriteLine(c);//3
 } 
}

using System;
     
public class Program
{
 public static void Main()
 { 
  string a = "hello";
  int b = 3;
  var myVar = (a, b);
    Console.WriteLine(myVar.a);//hello
  Console.WriteLine(myVar.b);//3
  Console.WriteLine(myVar.Item1);//hello
 } 
}