Comment (by Roland Haas):

I tried reproducing this using the master branch of Carpet with the compilers available on my workstation:

• g++-9 (Debian 9.2.1-22) 9.2.1 20200104 compiles without error
• g++-8 (Debian 8.3.0-26) 8.3.0 compiles without error
• g++-7 (Debian 7.5.0-3) 7.5.0 compiles without error

Switching to ET_2016_11 I find that:

• g++-7 (Debian 7.5.0-3) 7.5.0 fails with the error your describe
• g++-8 (Debian 8.3.0-26) 8.3.0 fails with the error your describe
• g++-9 (Debian 9.2.1-22) 9.2.1 20200104 fails with the error your describe

Since the version you are using (ET_2016_11) is 3 years old, there have been quite a few changes since then. However if I had to bet I’d say that git hash 986b01b2 "Move CarpetLib types and functions into a new namespace CarpetLib" of carpet is the one that makes it work in master.

@Samuel Tootle , you have some options:

1. switch to use master (at least for Carpet)
2. ask @David Radice whether a newer version of the ET can be used (anything starting with ET_2019_03 will do) with THC
3. try and cherry pick the commit I pointed out and hope for the best

Since this is a very old release we (the ET maintainers) are unlikely to backport a fix to it.

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Ticket URL: https://bitbucket.org/einsteintoolkit/tickets/issues/2315/issues-compiling-with-gcc73-with-c-17