To: J3                                                     J3/20-137
From: Richard Bleikamp
Subject: UTI-15
Date: 2020-September-30

Reference: 20-122r1

Background:
In F202x, the list of variables described below are now assigned
values with intrinsic assignment semantics, which will, for deferred
length allocatable character variables, often require deallocating
the variable (if allocated) and allocating it with the "appropriate"
length for the value to be assigned.  In F2018, these variables were
assigned a value with appropriate truncation or blank padding using
the existing allocated storage/length.
  Character variables affected (if deferred len, and allocatable)
  - those specified in IOMSG= and ERRMSG= clauses,
  - those passed into certain intrinsic routines
    (DATE_AND_TIME, EXECUTE_COMMAND_LINE, GET_COMMAND,
    GET_COMMAND_ARGUMENT, GET_ENVIRONMENT_VARIABLE), and
  - those used as the unit in an internal WRITE statement.

Here's an example that has a different interpretation under F2018
than F202x.

program uti15
  character (len=:), allocatable :: msg
  allocate(character(len=100)::msg)
  write(msg, "('this is a test')")   ! F202x reallocates msg
  write(*,*) msg(99:99)    ! a blank under F2018, zero length
                           ! value under F202x
end

Edits to address UTI-15 (against 20-011) follow.

{4.3.3}
[27:21-23], replace that paragraph with these new paragraphs, and
remove the Unresolved Technical Issue 015 note.

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Except as identified in this subclause, this document is an upward
compatible extension to the preceding Fortran International
Standard, ISO/IEC 1539-1:2018 (Fortran 2018).  A standard-conforming
Fortran 2018 program remains standard-conforming under this document.

The following Fortran 2018 feature may have a different
interpretation under this document.

After an allocatable deferred length character variable is assigned
a value in an IOMSG= or ERRMSG= clause, as the unit in an internal
WRITE statement, or as an INTENT(OUT) argument in an intrinsic
subroutine, that variable may be of shorter or longer length under
this document than under Fortran 2018, since this document specifies
intrinsic assignment semantics for these assignments.

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