Adding const-ness after the fact in C++

Question

Possible Duplicate:
Is there some ninja trick to make a variable constant after its declaration?

Consider the following minimal example:

void MutateData(std::string&);

int main()
{
  std::string data = "something that makes sense to humans.";

  ::MutateData(data); // Mutates 'data' -- e.g., only changes the order of the characters.

  // At this point, 'data' should never be changed.
  // Mixing the above with const-correct code seems ugly.
}

Currently, I'm doing:

namespace
{
  std::string PrepareData(std::string data)
  {
    ::MutateData(data);

    return data;
  }
}

int main()
{
  const std::string data = ::PrepareData("something that makes sense to humans.");
}

What are some elegant solutions to simulating const beyond the point of declaration?

---

EDIT: I forgot to clarify that I can't easily (not my code) change MutateData.

Answer 1

What about:

string MakeData(string const&)
{
    ...
    return string(...);  // for return value optimization
}

followed by

int main()
{
    string const& str = MakeData("Something that makes sense to humans");
}

The difference with what you do is using a const reference, and only one function. If you cannot change MutateData, do what you suggested (with the const reference though)

Answer 2

You can use a const reference.
Take a look at http://herbsutter.com/2008 for an explanation about why it works.