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.

What about a Dictionary<string,object>, where the string is the name of the variable? — Oded
– Oded, Commented Aug 1, 2010 at 19:22
+1. can somehow use C#4's actual named params? ParamTest(customer: customer, purchase:purchase) — mpen
– mpen, Commented Aug 1, 2010 at 19:29

Andrei Rînea · Accepted Answer · 2010-08-01 19:38:08Z

5

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

answered Aug 1, 2010 at 19:38

Andrei Rînea

20.9k18 gold badges124 silver badges172 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Andrei Rînea Over a year ago

You can also reorder parameters in the call :)

ProfK Over a year ago

I wish I could vote Mark up as well, but his is not an answer. Thanks, this is my chosen route.

Andrei Rînea · Accepted Answer · 2010-08-01 19:24:21Z

0

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.

answered Aug 1, 2010 at 19:24

Andrei Rînea

20.9k18 gold badges124 silver badges172 bronze badges

4 Comments

mpen Over a year ago

could use an anonymous object instead in c#4

Andrei Rînea Over a year ago

yes, but obtaining its members and their names inside ParamsTest is not a simple task - it involves reflection

ProfK Over a year ago

Or I could just use a Dictionary<string, object> :-)

Andrei Rînea Over a year ago

You can also reorder parameters in the call :)

snurre · Accepted Answer · 2010-08-01 19:32:22Z

0

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 });

answered Aug 1, 2010 at 19:32

snurre

3,1152 gold badges26 silver badges31 bronze badges

3 Comments

Andrei Rînea Over a year ago

Just as in my anonymous type sample, you don't really have type safety, also you don't have parameter naming. Also, you can be shorter in syntax from "new object[] { ... }" to "new [] { ... }"

ProfK Over a year ago

I really, really need parameter naming.

snurre Over a year ago

Then I think Oded's suggestion of Dictionary<string,object> is your easiest option

Collectives™ on Stack Overflow

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

3 Answers 3

2 Comments

4 Comments

3 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

2 Comments

4 Comments

3 Comments

Your Answer

Sign up or log in

Post as a guest

Related