#include<iostream>
#include<cstdio>   
#include<string>
#include<functional>  /* requires -std=c++14 */
using namespace std;

/*          CLOSURES PROGRAMMING ASSIGNMENT, PART II

 Unlike with languages such as Python and Java, C/C++ programmers must
be keenly aware of where in memory their data are stored, and of their
LIFETIME.  The lifetime of a value is how long it's guaranteed to be
at the same location in memory.  The lifetime ends when, for example,
a value gets popped from the stack at the end of a function call, or
deallocated from the heap.  The value may persist in memory
momentarily after its lifetime ends but is unusable as it will be
overwritten.
...
*/

// SOLUTION: key is to first capture name, balance by value so they're
// copied into closure before getting popped from the stack. But under
// this context, the deposit, withdraw and balinquiry functions must capture
// balance by reference.  So all that's needed is to define these "methods"
// inside the public_interface function instead of outside.  In addition,
// the public_interface must be marked mutable because it contains
// procedures that mutate the free variable balance. (The balance in the
// public_interface closure cannot be const).

auto newaccount = [](string name, double balance) {
  auto public_interface =
    [=](const string& request) mutable {

      function<double()> balinquiry = [&name,&balance]() {
        printf("%s has a balance of %.2f\n",name.c_str(),balance);
        return balance;
      };
      function<void(double)> deposit = [&balance](double amt) mutable { 
        if (amt>0) balance+=amt;   
      };  // mutable means function could mutate free variables
      function<void(double)> withdraw = [&balance](double amt) mutable {
        if (amt>0 && amt<=balance) balance-=amt;
      };
      function<void(double)> dummyfun = [&balance](double x) mutable {balance+=0;};

      if (request=="deposit") {
        return deposit;
      }
      else if (request=="withdraw") {
        return withdraw;
      }
      else if (request=="inquiry") {
        balinquiry();
      }
      return dummyfun;  // this is required for type-consistency
  };
  return public_interface;
};//newaccount

int main() {
  auto myaccount = newaccount("Liang",1000);
  auto youraccount = newaccount("Student",2000);
  myaccount("inquiry");      // SHOULD print Liang has a balance of 1000
  youraccount("inquiry");    // SHOULD print Student has a balance of 2000
  myaccount("withdraw")(300);
  myaccount("deposit")(100);
  myaccount("inquiry");      // SHOULD print Liang has a balance of 800
  return 0;
}//main