Read protection

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Read protection is a technique for enforcing the immutability of an object in a given time interval. A class A must be designed for read protection by deriving it from ReadProtected<A>, and by calling ReadProtected<A>::readProtect() from the mutating functions of A. The desire to make an object of type A immutable is expressed by holding a ReadPtr<A> to the object. The immutability of the object is then enforced at those times when there exists at least one ReadPtr<A> to the object. Enforcing immutability means generating a run-time assertion when immutability would be violated. The ReadProtected<A> is implicitly convertible to ReadPtr<A>. This is the only way to obtain original ReadPtr<A>‘s; the remaining ones are copies of other ReadPtr<A>‘s.

Example

#include "pastel/sys/read_protected.h"

using namespace Pastel;

class A
: public ReadProtected<A>
{
public:
    void mutate()
    {
        readProtect();
    }

    integer query() const
    {
        return 0;
    }
};

class B
{
public:
    explicit B(const A& a)
    : a_(a)
    {
    }

private:
    ReadPtr<A> a_;
};

int main()
{
    A a;
    // Ok.
    a.query();
    // Ok.
    a.mutate();

    B b(a);
    // Ok.
    a.query();
    // Error.
    a.mutate();

    return 0;
}

Files

Read protection

read_protected.h