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Re: using Ctrl::Add; required for templates / overloaded virtual functions [message #27074 is a reply to message #27070]

Thu, 24 June 2010 14:13

tojocky
Messages: 607
Registered: April 2008
Location: UK

Contributor

kohait00 wrote on Thu, 24 June 2010 13:18

hi mrjt,

sure this one works, because Mid offers own Add(Ctrl&) *additionally* and so does my app with the Ctrls that either *dont* have own Add() overloads at all or have additional override Add(Ctrl&) properly (virtual or not, no matter), but it does not work with those only having incompatible Add() overloads.

just comment out Mid::Add(Ctrl&) and leave only Add(int) in Mid...boom.

i dont even need to access it at Top level (this would represent my template class, Mid is a CtrlLib Ctrl, Base is Ctrl implementation, thanks for breaking this one down Smile

, so Top can go...

struct Base {
	int result;
	virtual void Add(Ctrl &) { result = 1; }
};

struct Midd : public Base{
	//virtual void Add(Ctrl &) { result = 2; } //EITHER this, virtual or not, no metter
	using Base::Add; //OR this, saves compilation preserving complete Add overloads pool for compiler
	void Add(int)			{ result = 4; }
	void Nothing()   { result = 10; }
};

GUI_APP_MAIN
{
	Label l;
	Midd md;
	
	//option 1: << desired >>
	void (Midd::* mfp)(Ctrl &) = &Midd::Add; //problems even if Mid, not only Top
	(md.*mfp)(l);
}

i think this is more of a coding guideline, trying to sum up:

option 1:
when overloading (not overriding) a public virtuel base class function, be sure to have a proper override for it as well (maybe just calling base function)
or place a "using" statement to help compiler keep at least the public fnctions pool complete througout the hierarchy.

option 2:
use different function names

Very nice observation!

I made some tests and work perfectly:

struct Base1 {
	int result;
	virtual void Add(Ctrl &) { result = 1; }
	virtual void Add(int)			{ result = 2; }
	virtual void Add()			{ result = 3; }
};

struct Midd : public Base1{
	//virtual void Add(Ctrl &) { result = 2; } //EITHER this, virtual or not, no metter
public:
	virtual void Add(int)			{ result = 4; }
	void Nothing()   { result = 10; }
private:
	using Base1::Add; //OR this, saves compilation preserving complete Add overloads pool for compiler
};

GUI_APP_MAIN
{

	Label l1;
	Midd md1;
	
	//option 1: << desired >>
	void (Midd::* mfp1)(Ctrl &) = &Midd::Add; //problems even if Mid, not only Top
	(md1.*mfp1)(l1);
	Exclamation(Format("%d", md1.result));
	
	void (Midd::* mfp12)(int) = &Midd::Add; //problems even if Mid, not only Top
	(md1.*mfp12)(3);
	Exclamation(Format("%d", md1.result));
	
	void (Midd::* mfp13)() = &Midd::Add; //problems even if Mid, not only Top
	(md1.*mfp13)();
	Exclamation(Format("%d", md1.result));
}

and output are:

1
4
3

Thank you!

P.S. Maybe it is a bug of C++ if not compiling without using?

[Updated on: Thu, 24 June 2010 14:15]

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