C# syntax ignoring a parameter, asking of possibilities

Question

Having

public static void Search(string name, int age = 21, string city = "Tehran")
{
    MessageBox.Show(String.Format("Name = {0} - Age = {1} - City = {2}", 
        name, age, city));
}

I want to call Search method using name and city parameters to keep the default value of age.

AFAIK parameter should be referred by name

Search("Mahdi", city: "Mashhad");

I want to know if it is possible to make the call without specifying value for age and also without calling city by name? I mean something like jumping over a parameter, something like :

or

Search("Mahdi",,"Mashhad");

I've seen almost similar behavior for for loop

for (int i = 0; ; i++) { some code; }

or any other syntax that matches the case?

No, it's not possible. `for` loop does not accepting any parameters - this behavior is not similar — Sergey Berezovskiy, Mar 14 '14 at 07:19

score 4 · Answer 1 · answered Mar 14 '14 at 07:19

4

Simply create an overload which takes two string parameters like this:

public static void Search(string name, string city)
{
    Search(name, 21, city);
}

public static void Search(string name, int age = 21, string city = "Tehran")
{
    MessageBox.Show(String.Format("Name = {0} - Age = {1} - City = {2}", 
        name, age, city));
}

And call it like this:

Search("Mahdi", "Mashhad");

answered Mar 14 '14 at 07:19

p.s.w.g

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Instead of duplicating default value you can call `Search(name, city: city)` – Sergey Berezovskiy Mar 14 '14 at 07:22
1

@SergeyBerezovskiy I considered that, but unless you change the parameter names also, that would result in an infinite recursion. – p.s.w.g Mar 14 '14 at 07:24
@p.s.w.g I think the compiler is smart enough to catch that, it does not enter the recursion at all. – Mahdi Tahsildari Mar 14 '14 at 07:27
@MahdiTahsildari Well, I tested this code using `Search(name, city: city)` inside the first overload, and yes, it did result in recursion. However if you change the name of the `city` parameter in the first overload then it works fine. – p.s.w.g Mar 14 '14 at 07:31
@p.s.w.g yep, you are right - I didn't notice self call here – Sergey Berezovskiy Mar 14 '14 at 07:34
@p.s.w.g yeah didn't notice it. – Mahdi Tahsildari Mar 14 '14 at 07:36

nuclear sweet · Accepted Answer · 2014-03-14T07:34:10.847

2

Change it to

public static void Search(string name, string city = "Tehran", int age = 21)
{
    MessageBox.Show(String.Format("Name = {0} - Age = {1} - City = {2}", 
        name, age, city));
}

Now you can use it as

Search("Mahdi", "Mashhad");

Optional parameters are defined at the end of the parameter list, after any required parameters. http://msdn.microsoft.com/en-us/library/dd264739.aspx

edited Mar 14 '14 at 07:34

answered Mar 14 '14 at 07:24

nuclear sweet

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No I meant rational Idea :) argumentative with that meaning. Among all the answers this one is more logical, less code and everything in its place. Thanks. – Mahdi Tahsildari Mar 14 '14 at 07:37
1

@MahdiTahsildari i just missunderstand it because of my english skills, im glad that helps you. – nuclear sweet Mar 14 '14 at 07:42

score 1 · Answer 3 · answered Mar 14 '14 at 07:26

1

You could use a nullable int for age. Like this:

public static void Search(string name, int? age = null, string city = null)
{
    MessageBox.Show(String.Format("Name = {0} - Age = {1} - City = {2}", 
        name, age ?? 21, city ?? "Tehran"));
}

Then you could call the following combinations:

Search("Mahdi");
Search("Mahdi", 20);
Search("Mahdi", null, "Cairo");

which would use age=21 and city="Tehran" for the default values.

answered Mar 14 '14 at 07:26

Phillip Ngan

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looks good but if we do this then what's the point of optional parameters? – Mahdi Tahsildari Mar 14 '14 at 07:29
If all the arguments are non-optional, you would have to supply all three parameters all the time. Like: `Search("Mahdi", null, null );` – Phillip Ngan Mar 14 '14 at 07:43

C# syntax ignoring a parameter, asking of possibilities

3 Answers3