How to break your code easily a.k.a my params hell

26 Jun 2010 1 mins .NET, C#

Today I faced a behavior I have no idea exists. It’s more or less ambiguity between method with some parameters and one using params. Why more or less? Well, because it surely described in C# specification (“best match” or something similar to it). But I hadn’t know I should think about it until I was debugging weird behavior.

Let’s start with simple class:

class Test
{
	public Test(params int[] foos)
	{
		Console.WriteLine("foos");
	}
	public Test(int foo, int bar)
	{
		Console.WriteLine("foo bar");
	}
}

And now some (mind blowing 😉) code:

new Test(1);
new Test(1, 2);
new Test(1, 2, 3);

If you see the code in the context you probably spot the problem easily. The second row will not call the params but the other constructor.

Which is “cool” until you’re doing some refactoring and you (as I did) add new constructor with params and everything starts behaving unexpectedly. Maybe this text will help somebody to realize this faster than I did. 😄

Jiří Činčura is .NET, C# and Firebird expert. He focuses on data and business layers, language constructs, parallelism, databases and performance. For almost two decades he contributes to open-source, i.e. FirebirdClient. He works as a senior software engineer for Microsoft. Frequent speaker and blogger at www.tabsoverspaces.com.