How to convert functionbody into lambda?

Question

I want to convert a function body into a lambda. But I don't know how you can implement this if statement into the lambda. I also dont know what is the best to use for this. Is it better to use std::find_if, std::find or something else.

void Inventory::RemoveFromInventory(std::string  item)
{
    //--bool to check if an item is in the inventory
    bool found = false;

    for (std::list<Item>::iterator i = m_Inventory.begin(); i != m_Inventory.end(); i++)
    {
        if (i->GetName() == item)
        {
            m_Inventory.erase(i);
            found = true;
            break;
        }
    }
    if (found == false)
    {
        std::cout << "item not in inventory!" << std::endl;
    }
}

Cann someone help me with this conversion problem?

out of curiosity, why do you want to do that? afaik lambdas are mainly syntactic sugar for functors, but if you already have written down the method, what do you gain? — 463035818_is_not_an_ai, Apr 27 '17 at 08:48
have a look at http://stackoverflow.com/questions/347441/erasing-elements-from-a-vector — Caleth, Apr 27 '17 at 08:48
this for a school assignment, we need to implemt lambda's as much as possible. Is this possible for thsi function? — Stieven Vermoesen, Apr 27 '17 at 08:51
...or do you maybe want to transform the for-loop into a `find_if`? I guess yes, also the answer given uses that interpretation... — 463035818_is_not_an_ai, Apr 27 '17 at 08:51
@Caleth please dont answer questions in comment. Anyhow your comment is same as the solution proposed in an already given answer — 463035818_is_not_an_ai, Apr 27 '17 at 08:52

Quentin · Answer 1 · 2017-04-27T08:58:34.477

3

So you want to search for an item that verifies a condition, check whether you found it, and erase it. That's a use case for std::find_if:

void Inventory::RemoveFromInventory(std::string item)
{
    auto const foundAt = std::find_if(
        begin(m_Inventory),
        end(m_Inventory),
        [&](Item const &i) { return i.GetName() == item; }
    );

    if(foundAt == end(m_Inventory)) {
        std::cout << "item not in inventory!\n";
    } else {
        m_Inventory.erase(foundAt);
    }
}

edited Apr 27 '17 at 08:58

answered Apr 27 '17 at 08:50

Quentin

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@Gruffalo `begin` and `end` are found by ADL. `find_if` is, too, but I personally prefer qualifying it. – Quentin Apr 27 '17 at 08:58
Shouldn't I add `using std::begin` and `using std::end` to make sure ADL works correctly? – Emerald Weapon Apr 27 '17 at 09:52
@EmeraldWeapon `using std::begin; begin(a);` is only needed when you need to support the case where `a` is a C-style array. – Quentin Apr 27 '17 at 10:12
How does `begin(m_Inventory)` resolve to `std::begin(m_Inventory)` in your example if `m_Inventory` is not in `std` namespace? – Emerald Weapon Apr 27 '17 at 13:11
@EmeraldWeapon the *type* of `m_Inventory`, `std::list`, is what matters :) – Quentin Apr 27 '17 at 13:12
I was missing that part, thanks for the clarification. – Emerald Weapon Apr 27 '17 at 16:44

How to convert functionbody into lambda?

1 Answers1