Group join Linq C#

Question

I am reading many sites to get a better idea of Linq -Group Join.

var customers = new Customer[]
{
    new Customer{Code = 5, Name = "Sam"},
    new Customer{Code = 6, Name = "Dave"},
    new Customer{Code = 7, Name = "Julia"},
    new Customer{Code = 8, Name = "Sue"}
};

// Example orders.
var orders = new Order[]
{
    new Order{KeyCode = 5, Product = "Book"},
    new Order{KeyCode = 6, Product = "Game"},
    new Order{KeyCode = 7, Product = "Computer"},
    new Order{KeyCode = 7, Product = "Mouse"},
    new Order{KeyCode = 8, Product = "Shirt"},
    new Order{KeyCode = 5, Product = "Underwear"}
};
        var query = customers.GroupJoin(orders,
          c => c.Code,
          o => o.KeyCode,
          (c, result) => new Result(c.Name, result));//why mention c here??

        // Enumerate results.
        foreach (var result in query)
        {
            Console.WriteLine("{0} bought...", result.Name);
            foreach (var item in result.Collection)
            {
                Console.WriteLine(item.Product);
            }
        }

I couldnt understand why it gives (c, result) ? what if wrote as (c,o) ?

Can anyone share ideas on this?

Answer 1

These are just names of arguments passed to Func. You can use any name you want if that makes code more clear for you ie:

        var query = customers.GroupJoin(orders,
        c => c.Code,
        o => o.KeyCode,
        (something1, something2) => new Result(something1.Name, something2));

as it will just pass arguments from two previous Funcs into last one that is Func<TOuter, IEnumerable<TInner>, TResult>, so in that case Func<Customer, IEnumerable<Order>, Result>.

It's the same as with such situation:

public Result DoStuff(Order nameMeAnyWayYouWant, Customer meToo)
{
    //do stuff here
}

Code from question is from: http://www.dotnetperls.com/groupjoin

I'm adding model classes that author skipped if anyone wants to elaborate and in case dotnetperls.com went down:

class Customer
{
    public int Code { get; set; }
    public string Name { get; set; }
}

class Order
{
    public int KeyCode { get; set; }
    public string Product { get; set; }
}

class Result
{
    public string Name { get; set; }
    public IEnumerable<Order> Collection { get; set; }
    public Result(string name, IEnumerable<Order> collection)
    {
        this.Name = name;
        his.Collection = collection;
    }
}