How call constructor inside other constructor?

Question

My class has quite some properties and one of my constructors sets them all, I want the default constructor to call this other one and use the set properties. But I need to prepare arguments first, so calling it from the header won't help.

Here's what I'd like to do:

public class Test
{
 private int result, other;
 // The other constructor can be called from header,
 // but then the argument cannot be prepared.
 public Test() : this(0)
 {
 // Prepare arguments.
 int calculations = 1;
 // Call constructor with argument.
 this(calculations);
 // Do some other stuff.
 other = 2;
 }
 public Test(int number)
 {
 // Assign inner variables.
 result = number;
 }
}

So this is not possible, does anyone know how to call my constructor to set parameters inside code? Currently I'm storing a copy of the object from the other constructor and copying all the properties, it's really annoying.

Answer 1

Yes. just pass the value 1 in the first call

public class Test
{ 
 private int result, other;
 public Test() : this(1) 
 { 
 // Do some other stuff. 
 other = 2; 
 } 
 public Test(int number) 
 { 
 // Assign inner variables. 
 result = number; 
 }

}

And why can't you prepare the argument?

public class Test
{ 
 private int result, other;
 public Test() : this(PrepareArgument())
 { 
 // Do some other stuff. 
 other = 2; 
 } 
 public Test(int number) 
 { 
 // Assign inner variables. 
 result = number; 
 }
 private int PrepareArgument()
 {
 int argument;
 // whatever you want to do to prepare the argument
 return argument;
 }
}

or... if the prepareArgument is to be called from the default constructor, then it cannot be dependent on any passed in arguments. If it is a constant, just make it a constant ...

public class Test
{ 
 const int result = 1;
 private int result, other;
 public Test() 
 { 
 // Do some other stuff. 
 other = 2; 
 } 
}

if it's value is dependent on other external state, then you might rethink your design... Why not calculate it before calling the constructor in the first place?

• MrFox: Din't think of putting the preperation in a seperate method, it's not ideal but it will work, thanks.
• Charles Bretana: And depending on how complex it is, it could also be expressed inside the this() cpnstruction
• Saeb Amini: Just a small note: PrepareArgument must be static in the second approach.

Answer 2

If you want to call a constructor, but can't do it from the header, the only way is to define a private Initialize method. It appears you are doing "real work" in your constructor, which is not the task of a constructor. You should think of a different way to achieve your goal as your way severely prohibits debugging and others from reading your code.

• Ed Swangren: Why are we talking about headers and C# in the same topic? (not you so much as the OP)
• Femaref: I meant the header of the constructor, ie. constructor chaining, and that should be the same he was talking about as well.

Answer 3

Sounds like a little refactoring will help. While you can't do exactly what you want to do, there are always alternatives. I realize your actual code might be more complicated than the code you gave, so take this for an example refactoring of your problem. Extracting all common code into a new SetVariables method.

public class Test
{
 private int result, other;
 // The other constructor can be called from header,
 // but then the argument cannot be prepared.
 public Test() : this(0)
 {
 // Prepare arguments.
 int calculations = 1;
 // Call constructor with argument.
 SetVariables(calculations);
 // Do some other stuff.
 other = 2;
 }
 public Test(int number)
 {
 // Assign inner variables.
 SetVariables(number);
 }
 private void SetVariables(int number)
 {
 result = number;
 }
}