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Telastyn

Multiple inheritance do's and don'ts

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Hello again, A few of my recent threads have reminded me once again how much farther I have to go in learning things. As part of that learning process I've been re-writing a part of my GUI which I found to be awkward in the past, this time utilizing inheritance. Alas, I fear I've gone overboard with the inheritance :D The render objects I have are arranged in an n-tree [I think? 1 parent, multiple children] Up until now I've created 5 classes:
base - Contains parent, children, virtual render(), virtual dtor
+rect - adds rectangle coords to base
++root - Root render object, adds renderer specific info such as the DX device to rect
++text - adds a string, font info, color, and text formatting to rect
+image - adds vertex and texture info to base
So far, so good; everything works as it's supposed to. Code duplication is by far less, and a lot of the awkward areas have become much more straightworward [in exchange for other areas becoming more complex...] Now I'm looking to create a class for textinput. I was originally planning on making it inherit from both text and image. Before starting though I looked through some multiple inheritance docs [from thinking in cpp 2] which was nice enough to detail some of the headaches and logistics involved with multiple inheritance with a common ancestor. It also noted that what I'm looking to do could probably be done with virtual base functions. Doing so looks as though it might be a little messy, but workable. While it looks as though I've designed myself into a corner a little, I'd like to impliment the MI textinput class to learn a bit before making it a standalone with image and text children or starting over if need be. Before that though, I'd like to ask others for a little feedback as to what to do and what to avoid when dealing with these situations [beyond the obvious, 'avoid the situation'].

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You'll want to virtually inherit from base so that textinput only gets one copy of it, instead of one from text (via rect) and one from image.


class Base {};
class Rect : public virtual Base {};
class Text : public Rect {};

class Image : public virtual Base {};

class TextInput : public Text, public Rect {};

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