Re: Useful applications for boolean increments?

Am 10/21/12 10:52 PM, schrieb Daniel Kr?gler:


I can only imagine one reason why someone would want to use operator++
on a bool variable, which would be that he wants to negate the value in
a single line:

bool negate (bool value) {
  return ++value;
}

Such negation could be used like this:

void OnSomeCheckboxClicked () {
  if (++checkboxState) {
    doSomeChecks ();
  }
}

instead of

void OnSomeCheckboxClicked () {
  checkboxState = !checkboxState;
  if (checkboxState) {
    doSomeChecks ();
  }
}

Apparently operator++ does not work like this (it seems to invoke
operator++ on the internal representation of a bool):

#include <iostream>
int main () {
    bool foo = false;
    std::cout << "\n" << foo;
    foo++;
    std::cout << "\n" << foo;
    foo++;
    std::cout << "\n" << foo;
}

prints
0
1
1

The only use case for operator++ on bool I could think of was the following:

#include <iostream>
#include <vector>

void print(const std::vector<int>& vec) {
    bool needComma = false;
    for (auto it = vec.begin(); it != vec.end(); ++it) {
        if (needComma++)
            std::cout << ", ";
        std::cout << *it;
    }
}

int main () {
    std::vector<int> v;
    v.push_back(1);
    v.push_back(2);
    v.push_back(3);
    print(v);
}

Admittedly, this is a bit far-fetched will probably yield wrong results
for large vectors if bool is implemented using 8bit values.

Regards,
Stuart

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