8ec3e5fb54
It's long been a guideline (and IIRC a Weff-c++ warning) that either all, or none, of the copy methods should be defined, but this became a standard warning in GCC9. Presumably to account for a later language change though I'm not sure which. I don't remember why the ChanMapping copy constructor can't just be a simple copy (it's just a map of POD), but figure it's safer to just copy what that does.
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