lua function to C++ function - c++

Question

I'm working on converting a lua program into a C++ program but I've hit a road block, I can't figure out how to convert this into C++
function newPool()
local pool = {}
pool.species = {} --imports data from local species = {}
pool.generation = 0
pool.innovation = Outputs
pool.currentSpecies = 1
pool.currentGenome = 1
pool.currentFrame = 0
pool.maxFitness = 0
return pool
end
I know many basics of both languages and i know it works in lua but i need it in C++. Can anyone help me?

Answer 1

Lua has something called Tables which allows you to add key-value pairs without a predefined struct as in C/C++. So the Lua code you posted is adding key-value pairs to pool (read comments in code):
local pool = {} -- Declare a new Table
pool.species = {} -- Add another Table to pool called 'species'
pool.generation = 0 -- Add the key 'generation' with value '0'
pool.innovation = Outputs -- Add the key 'innovation' with value 'Outputs'
pool.currentSpecies = 1 -- Add the key 'currentSpecies' with value '1'
pool.currentGenome = 1 -- Add the key 'currentGenome' with value '1'
pool.currentFrame = 0 -- Add the key 'currentFrame' with value '0'
pool.maxFitness = 0 -- Add the key 'maxFitness' with value '0'
In C++ you have several options. 1) you can create a struct and declare what you need (I'm guessing on some datatypes but if you have the full Lua program you can figure them out):
struct Pool
{
Species species; // You'll have to define Species in another struct
int generation;
SomeEnum innovation; // You'll have to define SomeEnum in an enum
int currentSpecies;
int currentGenome;
int currentFrame;
int maxFitness;
}
If you have a class then you can use the struct Pool shown below (add the struct Pool definition from above to the .h file below above class Kingdom):
// I'm doing this as a class since you are programming in C++ and I
// assume you will want to add more functions to operate on similar
// objects.
class Kingdom
{
public:
Kingdom();
Pool* NewPool();
private:
Pool _pool;
}
In your .cpp file:
#include "Kingdom.h"
Kingdom::Kingdom()
{
// _pool.species = whatever you define struct Species as
_pool.generation = 0;
_pool.innovation = SomeEnum::Outputs; // You'll have to define SomeEnum
_pool.currentSpecies = 1;
_pool.currentGenome = 1;
_pool.currentFrame = 0;
_pool.maxFitness = 0;
}
Pool* Kingdom::NewPool()
{
Pool* newPool = new Pool;
memcpy(newPool, &_pool, sizeof(Pool)); // Make a copy
return newPool; // Return the new copy
// The newPool value is dynamic memory so when the calling function is done
// with newPool it should delete it, example:
// Kingdom myKingdom;
// Pool* myNewPoolStruct = myKingdom.NewPool();
// ... do some coding here
// delete myNewPoolStruct;
}
Option 2) would be if all of your key-value pairs were the same type; i.e. all keys were std::string and all values were int. Remember, the Lua code is using Tables so you can create the equivalent in C++ with std::map<>. Then you could use std::map<std::string, int> as follows:
// In your .h file change
Pool* NewPool();
Pool _pool;
// to
std::map<std::string, int> NewPool();
std::map<std::string, int> _pool;
Then in your .cpp file change the constructor to:
Kingdom::Kingdom()
{
_pool["species"] = 0; // Some int representation of species
_pool["generation"] = 0;
_pool["innovation"] = 1; // Some int representation of Outputs
_pool["currentSpecies"] = 1;
_pool["currentGenome"] = 1;
_pool["currentFrame"] = 0;
_pool["maxFitness"] = 0;
}
std::map<std::string, int> NewPool()
{
std::map<std::string, int> newPool;
newPool = _pool; // Copy - double check this against std::map
return newPool; // Double check this is a true copy and not a pointer
}
With std::map you can create key-value pairs on the fly just like the Lua code you provided. In short, I'd go with the struct Pool approach because with std::map<> you'll have to remember strings which isn't good practice and your IDE should have intellisense which will always show you the contents of struct Pool whenever you hit the . or -> operators.