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Expose a Obj.last_variant_tag constant #6834

vicuna opened this issue Apr 8, 2015 · 1 comment


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commented Apr 8, 2015

Original bug ID: 6834
Reporter: @gasche
Assigned to: @mshinwell
Status: closed (set by @xavierleroy on 2016-12-07T10:49:15Z)
Resolution: fixed
Priority: low
Severity: tweak
Category: standard library
Monitored by: @diml

Bug description

It would be nice to advertise the value of the last-usable-tag (for non-constant constructors). Currently people just assume it is Obj.lazy_tag - 1, but this limit is not currently specified anywhere.

Additional information

This was prompted by Benjamin Grégoire changes in the vm_compute mechanism of Coq, after Maxime Dénès remarked the lack of check for out-of-bound tags.


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commented May 6, 2015

Comment author: @mshinwell

This is such a small change that it seems reasonable to add it to 4.02.2. I added two new values:


These should suffice for bounds checks.

@vicuna vicuna closed this Dec 7, 2016

@vicuna vicuna added the stdlib label Mar 14, 2019

@vicuna vicuna added the bug label Mar 20, 2019

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