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

user_95135 0
Viewed 34712

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.

const-correctness c++11 c++
8 Answers

Answers were pretty solid, but honestly I can't really think of a GOOD situation to use this in. However in the event you want to Pre-Calculate a constant which is basically what you are doing you have a few main ways You can do this.

First we can do the following. So the compiler will simply set CompileA# for us in this case it's 50, 100, and 150.

const int CompileA1 = EarlyCalc(1);
const int CompileA2 = EarlyCalc(2);
const int CompileA3 = EarlyCalc(3);

int EarlyCalc(int a)
{
    a *= 50;
    return a;
}

Now anything beyond that there's so many ways you can handle this. I liked the suggestion as someone else had mentioned of doing. 

void SomeFunc(int a)
{
    const int A = EarlyCalc(a);
    //We Can't edit A.
}

But another way could be...

SomeFunc(EarlcCalc(a));

void SomeFunc(const int A)
{
    //We can't edit A.
}

Or even..

SomeFunction(int a)
{
    a *= 50;
    ActualFunction(a);
}

void ActualFunction(const int A)
{
    //We can't edit A.
}
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