C# string insertions confused with optional parameters

Question

I'm fairly new to C#, and trying to figure out string insertions (i.e. "some {0} string", toInsert), and ran across a problem I wasn't expecting...

In the case where you have two constructors:

public MyClass(String arg1) { ... }

public MyClass(String arg1, String arg2) { ... }

Is it possible for me to use the first constructor with a string insertion?

...
toInsert = "def"
myClass = new MyClass("abc{0}ghi", toInsert)
...

Or will C# interpret this as the second constructor and pass a literal "abc{0}ghi" as the first argument?

Answer 1

Yes, this will be interpreted as just a second parameter.

The behavior you describe is called string formatting and everything that accepts strings in this style uses string.Format() in the background. See the documentation of that method for details.

To get the desired behavior, use this code:

myClass = new MyClass(string.Format("abc{0}ghi", toInsert));

Answer 2

Just do:

public MyClass(string format, params object[] args)
{
  this.FormattedValue = string.Format(format, args);
}

Answer 3

Or will C# interpret this as the second constructor and pass a literal "abc{0}ghi" as the first argument?

This is the right answer. I think If you use String.Format("abc{0}ghi", toInsert) then it will take the first constructor