Re: change const property through overloading - C / C++ / MFC Discussion Boards

Re: compile error about auto_ptr

George_George24-Feb-08 21:05

George_George

24-Feb-08 21:05

Any comments to http://www.codeproject.com/script/Forums/View.aspx?fid=1647&msg=2439369[^]?

regards,
George

Re: compile error about auto_ptr

Mark Salsbery24-Feb-08 9:14

Mark Salsbery

24-Feb-08 9:14

If you use VS 2008+, the TR1 extensions to C++ have a shared_ptr (like the Boost shared_ptr mentioned by
peterchen) which can be used in a vector.

Mark

Mark Salsbery
Microsoft MVP - Visual C++
Java | [Coffee]

Re: compile error about auto_ptr

George_George24-Feb-08 16:13

George_George

24-Feb-08 16:13

Thanks Mark,

My question is more about auto_ptr. Any comment to

http://www.codeproject.com/script/Forums/View.aspx?fid=1647&msg=2439351[^]?

regards,
George

change const property through overloading

George_George22-Feb-08 23:18

George_George

22-Feb-08 23:18

Hello everyone,

I have tried compiler allows to change const property of an overloaded method. Here is my proof of concept code.

My question,

1. is it good code or good practice?
2. It yse in (1), are there any practical usage of this type of "overloading"?

class Base {
public:
	const int foo() {return 200;};
};

class Derived : public Base {
public:
		int foo() {return 100;};
};

int main()
{
	Base b;
	Derived d;
	int rtn = b.foo();
	rtn = d.foo();

	return 0;
}

thanks in advance,
George

Re: change const property through overloading

Shog⁹23-Feb-08 4:45

Shog⁹

23-Feb-08 4:45

There's no real point to the code in your example, so of course it can't be said to be "good". However, i've used similar constructs in past, here are a couple of scenarios where they made sense:

When returning references to internal data, using a const and a non-const access method to return const and non-const references.
This is helpful when, for instance, most users of the API will hold only const references to the object implementing it, but in at least one scenario (a client that creates or modifies the object) there will be callers that hold a non-const reference and need non-const access to the internal data.

For private/protected methods: used to provide subtly different behavior to public access and mutator methods.
I was writing a wrapper class for INI access last night. Two different methods, GetValue() and SetValue(), both need to retrieve a section pointer from the data store. The Get method will not modify the section, and should fail if the section is not found, while the Set method will modify the section, creating it if it is not found. So, i added two GetSection() methods for use by the public API, one const, the other not, each implementing one of the needed behaviors.

But who is the king of all of these folks?

Re: change const property through overloading

George_George24-Feb-08 16:21

George_George

24-Feb-08 16:21

Thanks Shog9,

Your experience is good. But you are not talking about specific to overloading or overriding, but general rules, right?

regards,
George

Re: change const property through overloading

Shog⁹24-Feb-08 16:33

Shog⁹

24-Feb-08 16:33

George_George wrote:
But you are not talking about specific to overloading or overriding, but general rules, right?

Not at all. Consider my second example: without overloading, you could write two separate methods - GetSection() and FindOrCreateSection() - but that breaks the abstraction by requiring callers to explicitly specify when section creation is done. Overloading GetSection() to provide a const version that will simply fail if the section isn't found lets you keep the calling code relatively consistent for const and non-const scenarios.

But who is the king of all of these folks?

Re: change const property through overloading

George_George24-Feb-08 16:52

George_George

24-Feb-08 16:52

Thanks Shog9,

1.

You mean the following scenario will make componet more complex and coupled with caller?

Shog9 wrote:
that breaks the abstraction by requiring callers to explicitly specify when section creation is done.

2.

How about overriding? If we change some const property of some overridden methods (return values and input parameters), is that good practice or anti-pattern? Any practical values/scenarios?

regards,
George

Rogarding doubt C,C++,MFC

rowdy_vc++22-Feb-08 22:42

rowdy_vc++

22-Feb-08 22:42

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