Property door_to appears twice in CreatePropertyOffsets?

Technical Development
1

In 6M62, as part of Output.i6t, a routine called CreatePropertyOffsets is created. It has a lot of lines that look like:

...
valued_property_offsets-->list_together = 10;
valued_property_offsets-->short_name = 16;
valued_property_offsets-->plural = 22;
valued_property_offsets-->article = 28;
...

I noticed that one property (door_to) occurs twice:

...
valued_property_offsets-->door_to = 47;
...
valued_property_offsets-->door_to = 165;
...

I don’t really understand what that routine is doing. It appears to be run as part of the initialise memory rule at startup. However, as far as I can tell, door_to is the only property appearing twice.

A peek at the actual value in the array shows that it is set to 165, with the first assigned value overwritten by the second as would be expected.

Two questions:

  1. Does anyone know what is the purpose of this routine? (A pointer to documentation would be fine.)
  2. Why does door_to appear twice?
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2

No documentation, but you can see how @draconis was using valued_proprty_offsets and related info to do what introspection was possible on I7 properties in Programatically printing all properties associated with object?

It turns out that the property_metadata, attributed_property_offsets, and valued_property_offsets arrays don’t exist anymore in v10.

Don’t know, but I’d suspect that the first assignment is a bit of dead code that never got removed and went unnoticed 'cause it was doing no harm. (And the redundancy doesn’t exist in v10.)

3

Thanks, Zed. Do you happen to know what drives the equivalent functionality (i.e. storing associations between properties and classes) in v10? (EDIT: It appears that this whole subsystem is significantly different in 10.1. Each property is given its own independent array.)

I think I have an idea of what CreatePropertyOffsets is doing: It’s storing the starting points (keyed by I6 property) of subarrays stored in the array property_metadata. Each subarray defines which specific objects and kinds are allowed to have that property (see WhetherProvides() and ScanPropertyMetadata()).

Looking at the way that property_metadata is defined:

Array property_metadata -->
...
    ! offset 47: property door_to
    "other side" K4_door NULL
...
    ! offset 165: property door_to
    "<nameless>" K4_door NULL
...

it appears that the double mention is an artifact of the twin uses of the door_to I6 property as both a default property of doors (originating in compiler hardcoding?) and from the declaration of an other side property mapped to I6 door_to in the the Standard Rules (Section SR1/5 - Doors).

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