How to null check c# 7 tuple in LINQ query?

user_2312877 0
Viewed 29199

Given:

class Program
{
    private static readonly List<(int a, int b, int c)> Map = new List<(int a, int b, int c)>()
    {
        (1, 1, 2),
        (1, 2, 3),
        (2, 2, 4)
    };

    static void Main(string[] args)
    {
        var result = Map.FirstOrDefault(w => w.a == 4 && w.b == 4);

        if (result == null)
            Console.WriteLine("Not found");
        else
            Console.WriteLine("Found");
    }
}

In the above example, a compiler error is encountered at line if (result == null).

CS0019 Operator '==' cannot be applied to operands of type '(int a, int b, int c)' and '<null>'

How would I go about checking that the tuple is found prior to proceeding in my "found" logic?

Prior to using the new c# 7 tuples, I would have this:

class Program
{
    private static readonly List<Tuple<int, int, int>> Map = new List<Tuple<int, int, int>>()
    {
        new Tuple<int, int, int> (1, 1, 2),
        new Tuple<int, int, int> (1, 2, 3),
        new Tuple<int, int, int> (2, 2, 4)
    };

    static void Main(string[] args)
    {
        var result = Map.FirstOrDefault(w => w.Item1 == 4 && w.Item2 == 4);

        if (result == null)
            Console.WriteLine("Not found");
        else
            Console.WriteLine("Found");
    }
}

Which worked fine. I like the more easily interpreted intention of the new syntax, but am unsure on how to null check it prior to acting on what was found (or not).

c#-7.0 linq c#
10 Answers

In C# 7.3, it's very clean:

var result = Map.FirstOrDefault(w => w.a == 4 && w.b == 4);
if (result == default) {
    Console.WriteLine("Not found");
} else {
    Console.WriteLine("Found");
}
user_83304120

You need:

if (result.Equals(default)) Console.WriteLine(...

(c# > 7.1)

user_4600840

how i did it with c# 7.3

T findme;
var tuple = list.Select((x, i) => (Item: x, Index: i)).FirstOrDefault(x => x.Item.GetHashCode() == findme.GetHashCode());

if (tuple.Equals(default))
    return;

...
var index = tuple.Index;
user_26489070

Most of the answers above imply that your resulting element cannot be default(T), where T is your class/tuple.

A simple way around that is to use an approach as below:

var result = Map
   .Select(t => (t, IsResult:true))
   .FirstOrDefault(w => w.t.Item1 == 4 && w.t.Item2 == 4);

Console.WriteLine(result.IsResult ? "Found" : "Not found");

This sample uses C# 7.1 implied tuple names (and ValueTuple package for C# 7), but you can give the name to your tuple elements explicitly if required, or use a simple Tuple<T1,T2> instead.

user_3612820
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