It complains about not finding a match for the pair<> template class,
because the first parameter (this) is allegedly const. However, this
isn't a const method, so I suspect it is a compiler bug.
In order to move on, I slap on a harmless cast which will make this
particular compiler happy, and which should have no effects elsewhere,
but put it in a #if..#else..#endif macro to avoid warnings on others;
hopefully this also makes it easier to spot and remove in the future.
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