(j3.2006) ALLOCATE with MOLD: Default initializer and dynamic type

[Bill Long]

Hi Tobias,

Tobias Burnus wrote:
> Hello,
> 
> I have a question regarding ALLOCATE with MOLD where both the
> source-expr is polymorphic - and, thus, the allocate-object is as well.
> Executing the allocate statement, the allocate-object gets the same
> dynamic type as the source-expr:
> 
> "if source-expr is specied, each allocate-object is allocated with the
> dynamic type and type parameter
> values of source-expr"
> 
> For SOURCE, it gets the value of the source-expr - but for MOLD it does
> not. My interpretation is now that then the default-initialization of
> components kicks in - namely the one of the dynamic type. Is my
> interpretation correct?
> 

Yes. The relevant wording in 10-007 is at [454:28-29] list item (19)

"Allocation of an object that has a nonpointer default-initialized 
subcomponent, except by an ALLOCATE statement with a SOURCE= specifier, 
causes that subcomponent to become defined."

Since the allocate in your example below  does not have  a SOURCE= 
specifier, the initialization should occur.

Cheers,
Bill


> The program below prints with one compiler:
>  a= 0  b= 0
> though I had expected the answer to be
>  a= 1  b= 3
> 
> 
> If the latter is correct: How do other vendors plan to handle this?
> Adding another entry to the vtable? (Assuming that you also use a
> vtable.) Or can something smarter be done?
> 
> Tobias
> 
> 
> implicit none
> type t
>   integer :: a = 1
> end type t
> 
> type, extends(t) :: t2
>   integer :: b = 3
> end type t2
> 
> class(t), allocatable :: x, y
> 
> allocate (t2 :: y)
> select type (y)
>   type is (t2)
>     y%a = 44
>     y%b = 55
> end select
> 
> allocate ( x, mold=y)
> select type (x)
>   type is (t2)
>    print *, 'a=', x%a, ' b=', x%b
> end select
> end
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-- 
Bill Long                                           longb at cray.com
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