W8089 'type::operator<' must be publicly visible to be contained by a 'type' (C++)
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The type that is being used for an STL container has a private 'operator<'. The type that is being contained (type::operator) must be a public type.
For example, if you were trying to instantiate a class type "vector<blah>", the error would be:
'blah::operator<' must be publicly visible to be contained by a 'vector'