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

[via Digitalmars-d-bugs]

https://issues.dlang.org/show_bug.cgi?id=14592

--- Comment #3 from Kenji Hara <k.hara.pg at gmail.com> ---
(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.

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