Re: [sv-ec] proposal for mantis #1382 - shallow copy

Ray,

My comments are embedded below.

Neil



> 
> ------------------------------------------------------------------------
> 
> Section 7.11 Assignment, renaming, and copying
> 
> In 7.11, following the paragraph that begins:
> 
>                 The last statement has *new* executing a second time,
> thus creating a new object p2, whose class properties are copied from
> p1. This is known as a /shallow copy/. …
> 
> ADD the new paragraph
> 
>                 A /shallow copy/ executes in the following manner:
> 
> 1.        An object of the class type being copied is allocated. This
> allocation shall not call the objects constructor or execute any
> variable declaration initialization assignments.

[NK] Calling the class constructor can have side affects that occur outside of the
instance of the object being constructed. This includes triggering events,
assigning values to variables, etc. Do we really want to say that calling the
new method during a shallow copy will not actually call the new method? I think
that a lot of people would find this rather confusing.

When the new method has arguments the values of those arguments may be used to
assign values to class properties. These properties may then be used by the new
method to update variables outside of the class.

It seems to me that the new method should be called as the first step of
the creation of an object that specifies a shallow copy. It may be possible
for implementations to optimize this step such that a minimal number of
operations are performed. For example, in situations where the constructor
only sets the values of class properties, the call to new can be eliminated
since those property values will be over-written when the shallow copy takes
place.

This implies that variable initialization assignments should also take place.


> 
> 2.        All class properties, including the internal states uses for
> randomization and coverage are copied to the new object. Object handles
> are copied, this includes the object handles for covergroup objects (See
> clause 18). The internal states for randomization include the RNG state,
> the ‘constraint_mode’ status of constraints, the ‘rand_mode’ status of
> random variables, and the cyclic state of randc variables (See clause 13).

[NK] Don't handles only refer to class objects? This proposal is introducing
the notion of a handle to a covergroup.  I would expect each instance of the class
to have its own copy of any embedded covergoups. Using a shallow copy during the
construction of the object shouldn't change that.


> 
> 3.        A handle to the newly created object is assigned to the
> variable on the left-hand side.
> 
>  Note: A shallow copy does not create new coverage objects (covergroup
> instances). As a result, the properties of the new object are not covered.
> 
>  
> 
> MODIFY the example (following the paragraph)
> 
>               *class* A ;
> 
>   *integer* j = 5;
> 
> *endclass*
> 
> *class* B ;
> 
>   *integer* i = 1;
> 
>   A a = *new*;
> 
> *endclass
> 
> **class *C extend A ;
> 
> *  rand int *x;
> 
> *  constraint *cst1 { x < 10; }
> 
> *endclass*
> 
> *function* *integer* test;
> 
>   B b1 = *new*; // Create an object of class B
> 
>   B b2 = *new* b1; // Create an object that is a copy of b1
> 
>   C c1 = new; // Create an object of class C
> 
>   A c2, c3; // Declare class variables (null value)
> 
>   b2.i = 10; // i is changed in b2, but not in b1
> 
>   b2.a.j = 50; // change a.j, shared by both b1 and b2
> 
>   test = b1.i; // test is set to 1 (b1.i has not changed)
> 
>   test = b1.a.j; // test is set to 50 (a.j has changed)
> 
>   c1.x = 3;
> 
>   c2 = c1;  // c2 refers to the same object as c1
> 
>   c3 = new c2; // Creates a shallow copy of c1 (including property x)
> 
> *endfunction*
> 
>  
> 

-- 
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Neil Korpusik                                     Tel: 408-720-4852
Senior Staff Engineer                             Fax: 408-720-4850
Frontend Technologies - ASICs & Processors (FTAP)
Sun Microsystems
email: neil.korpusik@sun.com
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