One function that can use dynamic function swapping - c++

Question

This might sound a little convoluted, but here we go.
So, I have the following code:
void Utility::validateRangeAndModify(Pet pet, int checkint,
int numbertovalidate,
bool greaterorless)
{
if (greaterorless) {
if (numbertovalidate < checkint)
pet.getAttributes()->setPetHunger(0);
} else
if (numbertovalidate > checkint)
pet.getAttributes()->func(100);
}
Firstly, This code is designed to validate a single integer. That part is easy.
Then, what I want it to do is carry out a function depending on if the integer meets the condition or not. In this case, setPetHunger() is being set to either 0 or 100. The issue is, I have setPetHealth(), and setPetEnergy() too.
The function I want it to perform is the thing that I want to change.
For instance. This code will only work for my pets Hunger. It won't work for it's Health, Happiness, or any of it's other variables. and I have a ton of other variables.
I'm wondering if there is any way to achieve something like this:
void Utility::validateRangeAndModify(Pet pet,
int checkint,
int numbertovalidate,
bool greaterorless,
string functiontouse)
{
if (greaterorless) {
if (numbertovalidate < checkint)
pet.getAttributes()->setPetHunger(0);
} else
if (numbertovalidate > checkint)
pet.getAttributes()->FUNCTION_TO_USE(100);
}
I could use something like reflection for this in C#. However, I don't know an alternative function in c++

Answer 1

You can do it by passing the correct member function pointer as parameter to Utility::validateRangeAndModify as below:
void
Utility::validateRangeAndModify(Pet &pet, int checkint, int numbertovalidate,
bool greaterorless, void(Attrib::*memfun)(int)) {
^^^^^^^^^^^^^^^^^^^^^^^^^^
if(greaterorless) {
if(numbertovalidate < checkint) (pet.getAttributes()->*memfun)(0);
} else {
if(numbertovalidate < checkint) (pet.getAttributes()->*memfun)(100);
}
}
And then call it as (if Utility::validateRangeAndModify is not static use obj.validateRangeAndModify):
Utility::validateRangeAndModify(p, 10, 9, false, &Attrib::setPetHunger);
Utility::validateRangeAndModify(p, 10, 9, false, &Attrib::setPetThirst);
LIVE DEMO

Answer 2

You should use a function pointer:
void Utility::validateRangeAndModify(Pet pet, int checkint,
int numbertovalidate,
bool greaterorless,
void (*func)(int, attribs &))
{
if (greaterorless) {
if (numbertovalidate < checkint)
pet.getAttributes()->setPetHunger(0);
} else
if (numbertovalidate > checkint)
func(100, pet.getAttribs());
}
You and the client will agree on the prototype of the function that you will pass; in this case, the prototype will be void func(int, attribs &);
The client can write code like this:
void happiness(int level, attribs &a)
{
// some code here
}
Utility::validateRangeAndModify(..., happiness);
Now happiness willl be called by your validateRangeAndModify function.
NOTE: happiness is a free function. If it is a member function, mark it as static: then there won't be the extra this argument.

Answer 3

To keep this simple, I'm providing a really trivial program that uses std::bind, std::function, and std::placeholders to allow calls to a bound method. This keeps the correct this with the method and generally prevents nastiness.
#include <iostream>
#include <functional>
// bait class to catch bound function calls. Replace this with pet for OP's example
class TwoMethods
{
public:
void method1(int val)
{
std::cout << "Method 1 received " << val << std::endl;
}
void method2(int val)
{
std::cout << "Method 2 received " << val << std::endl;
}
};
// utility function that will operate on a bound function
void utilityfunction(std::function<void(int)> func)
{
// calls passed function. Quietly handles bound this parameter and replaces
// placeholder with 42
func(42);
}
int main()
{
TwoMethods obj;
// call utility function with appropriate object and method
// the std::placeholders::_1 lets the compiler know there is another parameter that
// will be supplied later
utilityfunction(std::bind(&TwoMethods::method1, obj, std::placeholders::_1));
utilityfunction(std::bind(&TwoMethods::method2, obj, std::placeholders::_1));
}
In OP's case:
void Utility::validateRangeAndModify(int checkint,
int numbertovalidate,
bool greaterorless,
std::function<void(int)> func)
{
switch (greaterorless)
{
case 0:
{
if (numbertovalidate < checkint)
{
func(0);
}
}
break;
case 1:
{
if (numbertovalidate > checkint)
{
func(100);
}
break;
}
}
}
And called something like:
validateRangeAndModify(42, 666, false,
std::bind(&Attributes::setPetHunger,
pet.getAttributes(),
std::placeholders::_1))