class PG::BasicTypeMapForResults::WarningTypeMap

def initialize(typenames)
	@already_warned = {}
	@typenames_by_oid = typenames
end

def typecast_result_value(result, _tuple, field)
	format = result.fformat(field)
	oid = result.ftype(field)
	unless @already_warned.dig(format, oid)
		warn "Warning: no type cast defined for type #{@typenames_by_oid[oid].inspect} format #{format} with oid #{oid}. Please cast this type explicitly to TEXT to be safe for future changes."
		unless frozen?
			@already_warned[format] ||= {}
			@already_warned[format][oid] = true
		end
	end
	super
end