Cannot add tuple to list

Question

I have a list of tuples and cannot add them to a list. What causes this compile error? https://dotnetfiddle.net/vhR3vP

    using System;
    using System.Collections.Generic;               
public class Program
{
    public static void Main()
    {
        Console.WriteLine("Hello World");
         List<Tuple<string,string,string,string,string,string,string,string>> ExecutionsDetailsTuple =new  List<Tuple<string,string,string,string,string,string,string,string>>(); // format executionid, symbol, quantity, price, tradedirection, orderaction, account, executiontime
        var person= Tuple.Create<string,string,string,string,string,string,string,string>("1","2","3","4","5","6","7","8");
        ExecutionsDetailsTuple.Add(person);
        
    }
}

compile error:

Compilation error (line 10, col 3): The best overloaded method match for 'System.Collections.Generic.List<System.Tuple<string,string,string,string,string,string,string,string>>.Add(System.Tuple<string,string,string,string,string,string,string,string>)' has some invalid arguments
Compilation error (line 10, col 30): Argument 1: cannot convert from 'System.Tuple<string,string,string,string,string,string,string,System.Tuple<string>>' to 'System.Tuple<string,string,string,string,string,string,string,string>'

Progman · Accepted Answer · 2021-03-06 18:42:00Z

2

The return type of Tuple.Create<> with eight arguments is defined as:

Tuple<T1,T2,T3,T4,T5,T6,T7,Tuple<T8>>

Notice the Tuple<T8> at the end. You think you would create a Tuple<T1,T2,T3,T4,T5,T6,T7,T8> instance with the Tuple.Create() method, but you are not.

As the number of generic parameters for the Tuple class is limited to eight, but there might be a requirement for more than eight values, the class is designed that way, that the 8th generic parameter must be a Tuple type. So the general structure will be: seven values plus an additional Tuple for the remaining values. Assuming you want to create a tuple of 25 values, you would build a chain of four Tuple instances (7+7+7+4).

When you want to use a tuple of eight values you have to change the type of your variable to List<Tuple<string,string,string,string,string,string,string,Tuple<string>>>.

answered Mar 6, 2021 at 18:42

Progman

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2 Comments

junkone Over a year ago

i tried it but i have this error. how do i fix it if i have to have tuple as last row? dotnetfiddle.net/WSa0bl

Progman Over a year ago

@junkone There is no overload of Tuple.Create() which takes nine arguments. You have to use the Tuple constructor to create a Tuple with eight values, where the 8th argument is a Tuple of two values. This will result in a tuple with 7+2 values.

Tomasz Juszczak · Accepted Answer · 2021-03-06 18:35:33Z

1

Tuples should not be used in "production code" unless you deal with CLI or some other you get your input from some other language.

Because of Generics limitations in C# Tuples can have at most 8 generic values. And as per documentation: The last element of an eight element Tuple must be a Tuple.

To remove this error, convert this tuple to class, or convert your tuple so it uses a Tuple as a last element

edited Mar 6, 2021 at 18:35

answered Mar 6, 2021 at 18:30

Tomasz Juszczak

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