I can not get the idea of how to create Array
template class properly in C++.
The problem is solely out of learning purposes.
Let me provide the code first.
Array.h
:
//Developed by Trofimov Yaroslav on 30.03.2018
#ifndef _ARRAY_H_TROFIMOV_
#define _ARRAY_H_TROFIMOV_
#include <string>
template<const size_t n, typename T>
class Array {
static unsigned __freeId, __quantity;
unsigned _id;
T** _array;
const size_t _n;
public:
typedef const bool (* const BooleanResultDelegate)(const T&);
class ArrayError {
const std::string _reason;
const size_t _index;
const size_t _maxIndex;
public:
ArrayError(const size_t index, const size_t maxIndex,const std::string& reason = "")
: _index(index), _maxIndex(maxIndex), _reason(reason) {}
std::string explanation(void) {
std::string res += "Index: " + std::to_string(_index) + "\n";
res += "Max index: " + std::to_string(_maxIndex) + "\n";
res += "Reason: " + _reason + "\n";
return res;
}
};
explicit Array<n, T>(T* arrayFiller = 0)
: _n(n), _array(new T*[n]), _id(++__freeId) {
if(arrayFiller != 0) {
for(size_t i(0); i < length(); ++i) {
_array[i] = new T(*arrayFiller);
}
} else {
for(size_t i(0); i < length(); ++i) {
_array[i] = arrayFiller;
}
}
reportIfDebug<n, T>(*this, "created");
++__quantity;
}
explicit Array<n, T>(const T& arrayFiller)
: _n(n), _array(new T*[n]), _id(++__freeId) {
for(size_t i(0); i < length(); ++i) {
_array[i] = new T(arrayFiller);
}
reportIfDebug<n, T>(*this, "created");
++__quantity;
}
Array<n, T>(const Array<n, T>& that)
: _n(n), _array(new T[n]), _id(++__freeId) {
for(size_t i(0); i < length(); ++i) {
(*this)[i] = new T[that[i]];
}
reportIfDebug<n, T>(*this, "created");
++__quantity;
}
~Array<n, T>(void) {
removeAll();
delete [] _array; _array = 0;
reportIfDebug<n, T>(*this, "deleted", false);
--__quantity;
}
T* operator[](const size_t i) {
if(i > length()) {
throw ArrayError(i, _n, "out of bounds exception");
}
return _array[i];
}
const T* operator[](const size_t i) const {
if(i > length()) {
throw ArrayError(i, _n, "out of bounds exception");
}
return _array[i];
}
const size_t length() const {
return _n;
}
const unsigned getID() const {
return _id;
}
void removeAll(BooleanResultDelegate removeCondition = 0) {
for(size_t i(0); i < length(); ++i) {
if(removeCondition == 0 || removeCondition(*_array[i])) {
delete [] _array[i]; _array[i] = 0;
}
}
}
};
template<const size_t n, typename T>
unsigned Array<n, T>::__freeId(0);
template<const size_t n, typename T>
unsigned Array<n, T>::__quantity(0);
template<const size_t n, typename T>
void reportIfDebug(
const Array<n, T>& instance,
const char* const message,
const bool showContent = true) {
#ifndef NDEBUG
std::cout << "========================================" << std::endl;
std::cout << typeid(instance).name() << ' '
<< message << ' '
<< "id: " << instance.getID() << std::endl;
if(showContent) {
std::cout << instance;
}
std::cout << "========================================" << std::endl;
#endif
}
template<const size_t n, typename T>
std::ostream& operator<<(std::ostream& os, const Array<n, T>& instance) {
for(size_t i(0); i < instance.length(); ++i) {
if(instance[i] == 0) {
os << "[" << i << "]: " << instance[i] << "\n";
} else {
os << "[" << i << "]: " << *instance[i] << "\n";
}
}
return os;
}
#endif
Main.cpp
:
//Developed by Trofimov Yaroslav on 30.03.2018
#include <iostream>
#include "Array.h"
int main(void) {
const Array<5, int> a(7);
std::cout << *a[2] << std::endl;
return 0;
}
What is the main problem right now - is that the client of my Array
class would have to use [indirection operator *
] and [0
value pointer check] to use the objects from array.
I do not want the client to do that. But, if I use reference instead of pointer as a return type of operator[]
I will not be able to return types which do not have copy constructor and I will return trash if nothing was put there before.
It seems like in Java
and C#
the problem is not fixed as well. The user is getting a reference to an object there and definitely should check for null
being returned. And [indirection operator *
] is called automatically there.