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

Question

I know the answer is 99.99% no, but I figured it was worth a try, you never know.

void SomeFunction(int a) {     // Here some processing happens on a, for example:     a *= 50;     a %= 10;     if(example())        a = 0;     // From this point on I want to make "a" const; I don't want to allow     // any code past this comment to modify it in any way. } 

I can do something somewhat similar with const int b = a;, but it's not really the same and it creates a lot of confusion. A C++0x-only solution is acceptable.

EDIT: another less abstracted example, the one that made me ask this question:

void OpenFile(string path) {     boost::to_lower(path);     // I want path to be constant now     ifstream ... } 

EDIT: another concrete example: Recapture const-ness on variables in a parallel section.

Answer 1

You could move the code to generate a into another function:

int ComputeA(int a) {   a *= 50;   a %= 10;   if (example())     a = 0;   return a; }  void SomeFunction(const int a_in) {   const int a = ComputeA(a_in);   // .... } 

Otherwise, there's no nice way to do this at compile time.

Answer 2

One solution would be to factor all of the mutation code into a lambda expression. Do all of the mutation in the lambda expression and assign the result out to a const int in the method scope. For example

void SomeFunction(const int p1) {    auto calcA = [&]() {     int a = p1;     a *= 50;     a %= 10;     if(example())        a = 0;     ..     return a;   };   const int a = calcA();   ... } 

or even

void SomeFunction(const int p1) {    const int a = [&]() {     int a = p1;     a *= 50;     a %= 10;     if(example())        a = 0;     ..     return a;   }();   ... }