Immutable object: Difference between revisions

Revision as of 18:55, 2 August 2025

Latest revision as of 16:47, 1 September 2025

Line 97:

=== C++ ===

In C++, a [[const-correctness|const-correct]] implementation of <code>CartShoppingCart</code> would allow the user to create instances of the class and then use them as either <code>const</code> (immutable) or mutable, as desired, by providing two different versions of the <code>items()</code> method. (Notice that in C++ it is not necessary — and in fact impossible — to provide a specialized constructor for <code>const</code> instances.)

<syntaxhighlight lang="cpp">

class CartShoppingCart {

private:

public:

Cart( std::vector<ItemMerchandise> items): items_(items) {};

public:

explicit Cart(std::vector<Item> items_;items):

items{items} {}

std::vector<ItemMerchandise>& items() { return items_; }

const std::vector<Item>& items() const { return items_items; }

}

const std::vector<Item>& items() const {

int ComputeTotalCost() const { /* return sum of the prices */ }

return *total_cost_items;

}

double computeTotalCost() const {

private:

return std::ranges::accumulate(

std::vector<Item> items_;

items | std::views::transform([](const Merchandise& m) -> double { return m.getPrice(); }), 0.0

);

}

};

</syntaxhighlight>

Line 119 ⟶ 128:

<syntaxhighlight lang="cpp">

class CartShoppingCart {

private:

public:

Cart( std::vector<ItemMerchandise> items): items_(items) {};

mutable std::optional<int> total_cost_totalCost;

public:

explicit Cart(std::vector<Merchandise> items): items{items} {}

const std::vector<ItemMerchandise>& items() const {
return items_items; }

int ComputeTotalCost() const {

if (total_cost_) {

return *total_cost_;

}

int total_costcomputeTotalCost() =const 0;{

for (const auto& item :if items_(!totalCost) {

totalCost = std::ranges::accumulate(

total_cost += item.Cost();

items | std::views::transform([](const Merchandise& m) -> double { return m.getPrice(); }), 0.0

);

}

return total_cost*totalCost;

}

total_cost_ = total_cost;

return total_cost;

}

private:

std::vector<Item> items_;

mutable std::optional<int> total_cost_;

};

</syntaxhighlight>