C++ complex initialization of a const value

Sometimes the initialization of a const value is complex and needs some extra code:

int value{default_value}; // initialize some defaults
if (checkSomeSophisticatedConditions)
{
  value = 8;
}
// use value
DoSomething(value);

// Since the value is determined at runtime, the only way to keep it unchanged is to write a function or to use another variable like this:
const int const_value {value};
value = 10;// This is valid

But actually in the business code the value should be const and the application should not change it’s value.

Using a second const value initialized by the non const value ist quiet easy but it needs some extra code and you will have a non const variable that might be used later by someone else. So it’s name is very important to descibe the usage.

Using a function separates the initialization logic from its usage. If you want to see what is going on here you have to look at two different places.

With C++11 we got lambdas and now can put a const value’s initialization into a closed scope next to it’s declaration.

const int const_value = [&]
{
  int value {default_value};
  if (checkSomeSophisticatedConditions)
  {
    value = 8;
  }
  return value;
}();

This issue is also discussed by Herb Sutter here.

You can test the code above here.