Re: New With Struct and Getting Class Object Pointers

[Vijay Nayar via Digitalmars-d-learn]

On Sunday, 30 September 2018 at 09:16:42 UTC, Nicholas Wilson 
wrote:
On Sunday, 30 September 2018 at 07:29:00 UTC, Vijay Nayar wrote:

Second question. const class variables may not be re-assigned, 
so if you need a variable that may be reassigned, but may 
never modify the underlying object, a const pointer can be 
useful.  However, it seems that when gets the address of a 
class variable, you do not get the underlying address of the 
class object.

&a = 0x7ffd0800acb8, a = 0x7fd6b05b0000, a.data=4
&a = 0x7ffd0800acd0, a = 0x7fd6b05b0000, a.data=4

     The stack ^   the heap^    data on the heap^
The address of the variable a on the stack has different values 
across function calls, its value (the reference to the class 
data) remains the same, as does the data itself.

Is there a way to either have a constant reference to a class 
that can be set to a new value, or is there a way to convert the 
class variable to a class pointer?

For example:

void main()
{
        class Thing {}
        class ThingSaver {
                // A const(Thing) could not be changed in 
setThing().
                const(Thing)* t;

                void setThing(in Thing thing) {
                        t = thing;  // ERROR converting to pointer type!
                }
                const(Thing) getThing() const {
                        return *t;
                }
        }
        
        Thing t1 = new Thing();

        ThingSaver saver = new ThingSaver();
        saver.setThing(t1);
        const(Thing) t2 = saver.getThing();
}