Re: AQ&S Guidance on pragma Elaborate_Body

["Nick Roberts" <Nick.Roberts@dial.pipex.com>]

Perhaps it could be summarised like this:

The 'call graph' (or 'call tree') of calls which occur during the
elaboration of the library units of a program cannot always be statically
determined.

There may be (and indeed, experience suggests, there will be) situations
where the potential call graph indicates a circularity (i.e. that there is
no order of elaboration which the compiler can determine will ensure that
an unelaborated subprogram is never called), but where there is, in fact,
an elaboration order in which normal execution of the program will not
cause an unelaborated subprogram to be called.

This is something which only the programmer can know: it cannot be
determined by the compiler. So, the programmer has got to tell the compiler
the order in which to elaborate the library units (and also, perhaps, has
to soothe the compiler's troubled brow, and reassure it that a call to an
unelaborated subprogram will not occur ;-).

Thus, elaboration pragmas are required.

As for 'state of the art': ask a soldier (/airman/sailor) whether he wants
weapon A, which is state-of-the-art, or weapon B, which is simple and
reliable. Which do you think he will choose? Or, to put it another way, if
you could buy Ada compiler product A, which is state-of-the-art (and costs
$30,000), or compiler product B, which requires elaboration pragmas (and
costs $3,000, and is more reliable anyway), which would you buy?

Nick.