[MacPorts] #60760: netgen @6.2.2004: fatal error: 'optional' file not found

[MacPorts]

#60760: netgen @6.2.2004: fatal error: 'optional' file not found
-------------------------+---------------------------------
  Reporter:  ryandesign  |      Owner:  MarcusCalhoun-Lopez
      Type:  defect      |     Status:  assigned
  Priority:  Normal      |  Milestone:
 Component:  ports       |    Version:
Resolution:              |   Keywords:
      Port:  netgen      |
-------------------------+---------------------------------

Comment (by chrstphrchvz):

 PR opened: https://github.com/macports/macports-ports/pull/8539

 Support for `<optional>` was [https://developer.apple.com/documentation
 /xcode-release-notes/xcode-10-release-notes introduced in Xcode 10].
 `<optional>` appears to be usable on macOS 10.12 and earlier using an
 alternative compiler, unless `std::optional::value` is needed.

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Ticket URL: <https://trac.macports.org/ticket/60760#comment:1>
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