[Bug c++/104111] [DR2589] Concept evaluation depends on context where it was first checked

["webrown.cpp at gmail dot com" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104111

--- Comment #10 from W E Brown <webrown.cpp at gmail dot com> ---
(In reply to Eric Estievenart from comment #9)

Sorry, but I find neither "weirdness" nor "spooky"-ness in the comment #9 code
as shown.  Rather, I believe it to be simply an example of a program that the
C++ standard would describe as "ill-formed, no diagnostic required."

A common, yet incorrect expectation that template instantiation somehow mirrors
function call semantics seems to me to lie at the heart of the
misunderstanding.  Hypothetically, if the above program were to be well-formed,
the compiler would need to instantiate the member template twice *with
identical template arguments* in order to obtain the expected two different
outcomes.  However, I recall no specification, in the C++ standard, that
requires such (relatively expensive!) duplication of compiler effort:  once a
template has been instantiated, the compiler seems fully entitled, say, to
cache the result of that instantiation and reuse that outcome as may be needed
during the remainder of that TU's compilation.

Put another way, defining the same function in two different ways (one
instantiation as deleted, one not) seems to be a form of ODR violation.

Perhaps the OP is also a manifestation of a similar misunderstanding; I've not
checked.  If so, I would respectfully recommend this PR be closed as invalid.