CODEWITHSUNDEEP
c++oopobjectinitialization
markzzz
markzzz

Reputation: 47995

How to Init a object within a CTOR after some other tasks?

I've my class MIDITest which got a member variable object called IPianoRoll:

class MIDITest : public IPlug 
{
private:
    IPianoRoll mPianoRoll;

public:
    MIDITest(IPlugInstanceInfo instanceInfo);
    ~MIDITest();
};

I need to invoke my custom CTOR of mPianoRoll:

IPianoRoll(IPlugBase *pPlug, int x, int y, int paramIdx) : IControl(pPlug, IRECT(x, y, x + kWidth, y + kHeight), paramIdx, IChannelBlend::kBlendColorDodge) {

}

only after some other task within MIDITest, such as:

MIDITest::MIDITest(IPlugInstanceInfo instanceInfo) : IPLUG_CTOR(kNumParams, kNumPresets, instanceInfo) {
    // SOME TASKS
    IGraphics *pGraphics = MakeGraphics(this, GUI_WIDTH, GUI_HEIGHT, PLUG_FPS);
    pGraphics->HandleMouseOver(true);
    AttachGraphics(pGraphics);

    // NOW I NEED TO "create it"
    mPianoRoll(this, 8, 8, kParamIDPianoRoll);
}

but of course I can't do mPianoRoll(this, 8, 8, kParamIDPianoRoll);.

I'd like to avoid pointer for this, since on "deleting" I got weird errors, and because (since I don't need pointers), I guess it's better to not use them and dynamic memory allocation.

I can't use Member Init List, since it will be called/used before the Task within the MIDITest CTOR.

What's the way?

Upvotes: 0

Views: 59

Answers (3)

Some programmer dude
Some programmer dude

Reputation: 409404

If the construction of mPianoRoll depends on some of the "tasks" that you perform in the constructor, then you could simply use the assignment operator and do e.g.

mPianoRoll = IPianoRoll(this, 8, 8, kParamIDPianoRoll);

Another possible solution is to make the "tasks" separate classes and have instances of them in the MIDITest class or have MIDITest inherit from them (as mixins), and use the construction initializer list for all initialization and tasks, ending with the mPianoRoll construction in the list.

Upvotes: 1

R Sahu
R Sahu

Reputation: 206707

One option is to initialize mPianoRoll with as much information as you have in initializer list and then update its state in the body of the constructor.

MIDITest::MIDITest(IPlugInstanceInfo instanceInfo) : IPLUG_CTOR(kNumParams, kNumPresets, instanceInfo),
                                                     mPianoRoll(this, 8, 8, <not sure what this would be> {
    // SOME TASKS
    IGraphics *pGraphics = MakeGraphics(this, GUI_WIDTH, GUI_HEIGHT, PLUG_FPS);
    pGraphics->HandleMouseOver(true);
    AttachGraphics(pGraphics);

    // update the state of mPianoRoll.
    mPianoRoll->someSetFunction(kParamIDPianoRoll);
}

Upvotes: 0

hauron
hauron

Reputation: 4668

You could move the other tasks into a base class. Base classes constructors will get processed first.

You could as well move them into a function, make it return a value, and use it to explicitly initialize another member in the initialization list.

Otherwise, it seems the other tasks are something the member variable is dependant upon, hence it may make sense to move it inside that member variable, or inside a wrapper object (that would be then normally initialized).

Upvotes: 1

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