Use a function to define an optional parameter

Question

Is it possible to use the return value of a function instead of a specific value as optional parameter in a function? For example instead of:

public void ExampleMethod(int a, int b, int c=10)
{
}

I want something like

private int ChangeC(int a, int b)
{
    return a+b;
}

public void ExampleMethod(int a, int b, int c=ChangeC(a,b))
{
}

Answer 1

No this is not possible. For a parameter to be optional the value must be a compile time constant. You can however overload the method like so:

private int ChangeC(int a, int b)
{
    return a + b;
}

public void ExampleMethod(int a, int b, int c) {}

public void ExampleMethod(int a, int b)
{
    ExampleMethod(a, b, ChangeC(a, b));
}

This way you don't have to deal with nullable value types

Answer 2

One of the ways:

private int ChangeC(int a, int b)
{
    return a+b; 
} 

public void ExampleMethod(int a, int b, int? c=null)
{
    c = c ?? ChangeC(a,b);
}