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How to return objects in class methods? #813

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kaysonwu opened this issue Sep 12, 2020 · 3 comments
Closed

How to return objects in class methods? #813

kaysonwu opened this issue Sep 12, 2020 · 3 comments

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@kaysonwu
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@kaysonwu kaysonwu commented Sep 12, 2020

I have the following 2 classes, now I need to encapsulate Hero into a node module

class Pet {
    public:
        Pet(const char* name);
        void Say();
    protected:
        const char* Name;
}

class Hero {
    public:
        Hero(const char* name);
        Pet GetPet();
    protected:
         const char* Name;
        Pet Pet;
}

I refer to the Wrapping C++ Object example, but I cannot complete the encapsulation of the GetPet method in the Hero class.

How can I implement GetPet to return the Pet object and customize its public methods?
@kaysonwu
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@kaysonwu kaysonwu commented Sep 12, 2020

I made an example 9_object_wrap, I found that the Pet object was free early, how can I solve it?

@mhdawson
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@mhdawson mhdawson commented Sep 22, 2020

@kaysonwu I think the problem is this line Pet(Pet::New(info.Env(), info[1].As<Napi::String>()))

This results in a a Pet JavaScript object that will only live as long as the method Hero::Hero is running since the object is not returned by the method and no JavaScript object references the object in the JavaScript heap. You do have a reference at the C++ level but that will not keep the object alive.

I think you need to use an ObjectReference https://github.com/nodejs/node-addon-api/blob/master/doc/object_reference.md. When hero is then destructed that should then result in the reference count to Pet being decreased and it being ready to be collected by the garbage collector.

@gabrielschulhof
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@gabrielschulhof gabrielschulhof commented Dec 4, 2020

@kaysonwu hopefully @mhdawson's suggestion solved the problem you were experiencing. Please re-open the issue if you believe there is any functionality in node-addon-api that needs to change to better support your use case!

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@gabrielschulhof @mhdawson @kaysonwu