#409 disable interp->result access support

[Don Porter]

Attached patch disables all code
that supports the legacy
interp->result field.

To restore it, compile with
USE_DIRECT_INTERP_RESULT_ACCESS
defined.

[Don Porter]

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Patch updated to include headers
and tests. (Thanks jenglish!)

[Don Porter]

[Don Porter]

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Second patch goes beyond
disabling to completely
removing support for
interp->result access.

[Don Porter]

[Jeffrey Hobbs]

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Without looking at the patch, I assume that this was done
without changing the size of the Tcl_Interp structure, which
would cause ABI issues.

[Don Porter]

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correct. no fields are removed by the patch.
(though public access to them is).

[Donal K. Fellows]

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I worry about old (broken) code that accesses that field
directly.
OK, it's broken, but I don't want to be the one explaining
that to users who find that their code no longer compiles
because of poorly written code that happens to not be
called. (That's quite possible with error handling code).

OTOH, I was planning to do this (or rather a total purge)
very early in the 9.0 cycle.

[Don Porter]

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changed your tune a little bit since
you wrote the comment at lines 632-639
of tclResult.c, then? :D

[Donal K. Fellows]

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"Consistency is the sign of a small mind"
:-p