4_global-user-data.md

Using GlobalUserData

Sharing data across modules

As described in the how it works section, ordinary globals cannot be used with hscpp.

To share data across modules (newly compiled shared libraries), we can use hscpp's GlobalUserData interface. For instance:

Global.h

#pragma once

#include "HotSwapObject.h"

class Global
{
public:
    HotSwapObject* pObj = nullptr;
};

Main.cpp

#include "hscpp/Hotswapper.h"
#include "HotSwapObject.h"
#include "Global.h"

int main()
{
    Hotswapper swapper;

    Global global;
    swapper.SetGlobalUserData(&global);
    ...
}

Anywhere in the codebase, the global instance can be accessed with:

hscpp::GlobalUserData::GetAs<Global>();

Fixing our previous example

With GlobalUserData and the Global class, we can amend our previous implementations:

HotSwapObject.cpp

...
#include "Global.h"
...
HotSwapObject::HotSwapObject()
{
    hscpp::GlobalUserData::GetAs<Global>()->pObj = this;
}
...

Main.cpp

...
int main()
{
    hscpp::Hotswapper swapper;
    ...
    Global global;
    swapper.SetGlobalUserData(&global);

    global.pObj = swapper.Allocate<HotSwapObject>();

    while (true)
    {
        global.pObj->Update();
        swapper.Update();
    }
}

Now, whenever a new object instance is created, the global pObj pointer will be updated, and no memory fault will occur.

Next, lets see how to serialize data and save state between runtime swaps.