How can I pass a variable number of named parameters to a method?

Question

I understand how to get the names of parameters passed to a method, but let's say I have a method declaration as follows:

static void ParamsTest(string template, params object[] objects)

and I want to use object/property names in my template for substitution with real property values in any of the objects in my `objects' parameter. Let's then say I call this method with:

ParamsTest("Congrats", customer, purchase);

I will only be able to retrieve two parameter names trying to fill out the template, viz, template, and objects, and the names of the objects in the objects collection are forever lost, or not?

I could require a List<object> as my second parameter, but I feel there is somehow a more elegant solution, maybe with a lambda or something. I don't know, I'm not used to using lambdas outside of LINQ.

Answer 1

You could define a parameters object :

public class ParamsTestParams {
    public string A { get; set; }
    public string B { get; set; }

    public static readonly ParamsTestParams Empty = new ParamsTestParams();
}

Change the methods signature to :

ParamsTest(ParamsTestParams parameters)

And call your method like so :

ParamsTest(new ParamsTestParams { A = "abc" });

or :

ParamsTest(new ParamsTestParams { B = "abc" });

or :

ParamsTest(new ParamsTestParams { A = "abc", B = "xyz" });

or :

ParamsTest(ParamsTestParams.Empty); // instead of null so you don't have to do null checks in the method's body

and so on.

Answer 2

I would probably just do it like this:

static void ParamsTest(string template, object[] objects)

and call it like this:

ParamsTest("Congrats", new object[] { customer, purchase });

Answer 3

Inpsired by Mark I can offer an anonymous type answer :

using System;

namespace ConsoleApplication5
{
    class Program
    {
        static void Main(string[] args)
        {
            ParamsTest(new { A = "a", B = "b"});
        }

        public static void ParamsTest(object o)
        {
            if (o == null)
            {
                throw new ArgumentNullException();
            }
            var t = o.GetType();
            var aValue = t.GetProperty("A").GetValue(o, null);
            var bValue = t.GetProperty("B").GetValue(o, null);
        }
    }
}

However this DOES have drawbacks :

• No type safety. I can pass in any object
• I can pass in an anonymous type with different members and/or types than those expected
• You should also do more checking than in this short sample