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Bug 14592 – [SPEC] Undocumented use of __U for mangling template constraints

Status: RESOLVED
Resolution: FIXED
Severity: major
Priority: P1
Component: dmd
Product: D
Version: D2
Platform: All
OS: All
Creation time: 2015-05-16T12:33:00Z
Last change time: 2015-05-17T12:30:58Z
Keywords: spec
Assigned to: nobody
Creator: ibuclaw

Comments

Comment #0 by ibuclaw — 2015-05-16T12:33:25Z

I've never come across it, so maybe it's just dead code in DMD.

Comment #1 by k.hara.pg — 2015-05-16T15:55:22Z

> I've never come across it, so maybe it's just dead code in DMD. __U is never used for any generated symbols, so it's not necessary to be documented in the spec. But in dmd front-end, it's actually used internally for a *temporary* instance which used on evaluation of template constraint.

Comment #2 by ibuclaw — 2015-05-16T17:22:21Z

(In reply to Kenji Hara from comment #1) > > I've never come across it, so maybe it's just dead code in DMD. > > __U is never used for any generated symbols, so it's not necessary to be > documented in the spec. > > But in dmd front-end, it's actually used internally for a *temporary* > instance which used on evaluation of template constraint. OK, so long as that is a guarantee, that should be fine. I just bumped into it when looking for other things that have been bugging me with the way some things are mangled. Could the __U be replaced with an @ ? That is one way to assert it never gets generated.

Comment #3 by k.hara.pg — 2015-05-17T12:03:21Z

(In reply to Iain Buclaw from comment #2) > Could the __U be replaced with an @ ? That is one way to assert it never > gets generated. I think it's not so good idea. @ is used for never mangled things (e.g. Terror, Tinstance, etfc), but __U is *actually* used, even it's only for the internal structure. A note for GDC and LDC: If a TemplateInstance object is "dummy" instance that using __U, its `members` field is NULL. In dmd code, it's excluded at ToObjFile visitor in toobj.c.

Comment #4 by ibuclaw — 2015-05-17T12:30:58Z

(In reply to Kenji Hara from comment #3) > (In reply to Iain Buclaw from comment #2) > > Could the __U be replaced with an @ ? That is one way to assert it never > > gets generated. > > I think it's not so good idea. @ is used for never mangled things (e.g. > Terror, Tinstance, etfc), but __U is *actually* used, even it's only for the > internal structure. > > A note for GDC and LDC: If a TemplateInstance object is "dummy" instance > that using __U, its `members` field is NULL. In dmd code, it's excluded at > ToObjFile visitor in toobj.c. OK, noted and will look into that. Suppose there's nothing left here to talk about.