Re: Q: access to subprogram

[fjh@murlibobo.cs.mu.OZ.AU (Fergus Henderson)]

bobduff@world.std.com (Robert A Duff) writes:

>Ada's access-to-subprogram types are rather severely restricted.  Yes,
>you can make a pointer-to-nested-proc, but that pointer can't survive
>longer than the immediately enclosing procedure.  [...]
>For a static-link implementation, a level-0 access-to-proc type can be
>implemented as a single address (of the procedure's code).   [...]
>A display implementation can always implement access-to-subp as a single
>address, at all levels.
>
>Does this help?

Yes, thanks.  I think I understand things now.

>Fergus Henderson <fjh@mundook.cs.mu.OZ.AU> wrote:
>>The way the Mercury implementation handles taking the address of a
>>generic instance in a shared generic is to package up the generic
>>instance data in basically the same way that the stack frame data in an
>>enclosing procedure is packed up when you take the address of a nested
>>procedure.  So as long as you are already committed to being able to
>>take the address of nested procedures, there is no distributed
>>overhead -- I think.
>
>Yes, this makes sense, I think, but doesn't it imply that level-0
>access-to-proc types have a static link attached?  That would constitute
>a distributed overhead, would it not, given the stuff I said above?  And
>make the interface to C more painful?

Yes, you're correct in all of the above.

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Fergus Henderson <fjh@cs.mu.oz.au>   |  "I have always known that the pursuit
WWW: <http://www.cs.mu.oz.au/~fjh>   |  of excellence is a lethal habit"
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