https://github.com/apple/swift/pull/16022 と https://github.com/apple/swift-corelibs-foundation/pull/1526 でちょうど解決されそうな話題？4.2にもバックポート済み

Turn on ‘as’ bridging on Linux. by millenomi · Pull Request #...

See https://forums.swift.org/t/bridging-for-swift-corelibs-foundation-on-linux/11994/1 for a full rationale. This is a work-in-progress patch to enable 'as', 'as?', 'as!' br...

Adopt ‘as’ bridging on Linux. by millenomi · Pull Request #15...

This patch adopts 'as' bridging on Linux. It requires apple/swift#16022 — see that PR for more details.