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From: Björn Karlsson (bjorn.karlsson_at_[hidden])
Date: 2001-11-06 09:25:58

> -----Original Message-----
> From: Gennadiy E. Rozental [mailto:rogeeff_at_[hidden]]
> Sent: den 5 november 2001 23:17
> To: boost_at_[hidden]
> Subject: [boost] Re: Class properties utility classes
> P.S. Does anybody know conformable alternative?

Sure; at least for some applications, some contained classes and with some
additional costs...

The property is (often) a public member, right?
So if you have the following classes:

struct BreakMyEncapsulation
        BreakMyEncapsulation(int iRO) : RO(iRO) {}
        readonly_property<int> RO;

struct BreakMyEncapsulationAgain
        BreakMyEncapsulationAgain(int iRO) : RO(iRO) {}
        const readonly_property<int> RO;

struct BreakMyEncapsulationIfYouCan
        BreakMyEncapsulationIfYouCan(int iRO) : RO(iRO) {}
        const readonly_property<const int> RO;

You can always do:

int main(int argc, char* argv[])
        BreakMyEncapsulation test1(1);
        BreakMyEncapsulationAgain test2(2);
        BreakMyEncapsulationIfYouCan test3(3);

        // Easy, but will a client ever try it?
        test1.RO = readonly_property<int>(42);
        // Harder, which might be acceptable for changing readonly values
from inside the class
        const_cast<readonly_property<int>&>(test2.RO) =
        // You are now entering undefined territory
        (readonly_property<int>&)test3.RO = readonly_property<int>(42);

        std::cout << test1.RO.get() << test2.RO.get() << test3.RO.get() <<
        return 0;

Of course, this involves creating a temporary that is assigned to the member
variable. If considered a bug, this can easily be avoided by protecting
assignment. I would rather view it as a feature, and document it as such.
This will no doubt raise new questions, such as efficient usage,
requirements for contained classes etc. Anyway, the issue probably needs to
be addressed.



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