boost::optional: unleash the power of C++ with Boost libraries.
Boost.Optional class is very close the boost::variant class but for only one type. boost::optional holds an array of char, where the object of type T can be an in-place constuctor. It has also a boolean flag to remember the state of the object (if is constructed or not).
To use this class, just add #include <boost/optional.hpp> to your program. See the example below:
#include <boost/optional.hpp>
#include <iostream>
#include <stdlib.h>
class lock{
//Note: constructor is private
explicit lock (const char * name) {
std::cout << name << " is locked \n";
}
public:
~lock () {
//release lock
}
void use() {
std::cout << "Success!\n";
}
static boost::optional<lock> acquire() {
if (rand()%2) {
return boost::none;
}
return lock("MyLock");
}
};
int main() {
srandom(5);
for (unsigned i = 0; i < 10; i++) {
boost::optional<lock> t =
lock::acquire();
if (t) {
t->use();
return 0;
} else {
std::cout << "... trying again \n";
}
}
std::cout << "Failure \n";
return -1;
}Boost.Optional class does not use dinamic allocation, and it does not require a default constructor for the underlying type.
##Further Information
Advantages of using the C++ Boost Libraries
Boost C++ Application Development Cookbook, by Antony Polukhin