J3/03-118

To: J3
From: UK Fortran panel
Subject: Edits for UK comment TC10 (Allocatable array assignment)
Date: 11 February 2003

Comment TC10 of the UK vote was:

    Treat the assignment to an allocatable array in the same way as to
    an allocatable array component

    Allocatable array assignment should be user-friendly the same way that
    allocatable component assignment is; that is, the destination array
    should be reallocated to the correct shape if it is of the incorrect
    shape. Thus, instead of having to say:
       DEALLOCATE (A)
       ALLOCATE (A(SIZE(COMPRESS(B))))
       A = COMPRESS(B)
    one should be able to say
       A = COMPRESS(B)
    and have the same effect (except that if A has the TARGET attribute
    and is already the same size as B, it should be reused rather than
    go through the allocate-deallocate cycle - for compatibility with
    F90/95).

For consistency, the above should apply to allocatable scalars (with
deferred type parameters) as well as to allocatable arrays.  I.e.

    Treat the assignment to an allocatable variable in the same way as
    to an allocatable component.

    Allocatable variable assignment should be user-friendly the same way that
    allocatable component assignment is; that is, a destination array
    should be reallocated to the correct shape if it is of the incorrect
    shape, and if the destination has deferred type parameters, it
    should be reallocated to have the correct values.

    A scalar example is that for
      CHARACTER(:),ALLOCATABLE :: A,B
    instead of
      DEALLOCATE(A)
      ALLOCATE(CHARACTER(LEN(B))::A)
      A = B
    one should be able to say
      A = B
     and have the same effect.




Here are the edits for this:

139:7. Replace the line by

   (2) Either <variable> shall be an allocatable array of the same rank
       as <expr> or the shapes of <variable> and <expr> shall conform,
       and

139:9+7. Last line of Table 7.8. Add "kind" before "type parameters".
   and after "<variable>" add
   "; each nonkind type parameter value shall be the same unless
   <variable> is allocatable and the corresponding type parameter
   is deferred"
{NOTE: "nonkind" should probably be "length" or whatever else is decided.}

139:28+. Add paragraph:

If <variable> is an allocated allocatable variable, it is deallocated
if <expr> is an array of different shape or any of the corresponding
nonkind type parameter values of <variable> and <expr> differ. If
<variable> is or becomes an unallocated allocatable variable, it is
allocated with the dynamic type and type parameters of <expr>, the
shape of <expr>, and with each lower bound (if any) equal to the
corresponding element of LBOUND(<expr>).