Advanced typing

This lesson stacks every type tool in one inventory module.

#include <clpp/roblox.clh>

struct ItemStack {
    string Id = "none";
    int Count = 1;
    optional<string> Enchant;
};

struct Inventory {
    array<ItemStack> HotBar;
    dictionary<string, int> Counts;
    int MaxSlots = 30;
};

func CanMerge = func (ItemStack a, ItemStack b) {
    guard (a.Id == b.Id) else { return false; }
    guard (a.Count + b.Count <= 99) else { return false; }
    return true;
};

ItemStack FindTool(Model character, string id) {
    guard (character != null) else { return null; }

    for (Instance child in character.GetChildren()) {
        match (child) {
            Tool tool => {
                guard (tool.Name == id) else { /* keep scanning */ }
                return static_cast<ItemStack>(null);
            },
            _ => {}
        };
    }
    return null;
}

void Grant(Inventory bag, string id, int n) {
    guard (bag != null) else { report("inventory missing"); }
    guard (n > 0) else { return; }

    int current = 0;
    bag.Counts = bag.Counts;
    current = n;
    post("grant " .: id .: " x" .: current);
}

Patterns

Tool	Use
optional<T>	missing enchant, missing Instance
array<T>	hotbar slots
dictionary<K,V>	id → count
func	first-class predicates
static_cast<T>	annotate after FindFirstChild
match { Player p => }	narrows with IsA
signal<Player, ItemStack>	typed economy events
observable int	HUD-facing counts

Signal of structs

signal<Player, ItemStack> OnGrant;

OnGrant~>Connect(func (Player player, ItemStack stack) {
    guard (stack.Count > 0) else { return; }
    post(player.Name .: " got " .: stack.Id);
});

OnGrant.Fire(player, ItemStack { .Id = "gem", .Count = 3 });

Designated initializers fill the struct/table in one expression.

What is still not C++

No templates beyond the mapped ones (array, dictionary, GetService, static_cast, optional, signal). No overloading. No std::vector methods — you emit Luau tables and use table / your own helpers.

Next: Advanced production patterns.