もう更新されてたのか。 https://developer.apple.com/library/content/documentation/Swift/Conceptual/Swift_Programming_Language/index.html Revisionはここ。 https://developer.apple.com/library/content/documentation/Swift/Conceptual/Swift_Programming_Language/RevisionHistory.html#//apple_ref/doc/uid/TP40014097-CH40-ID459

- Added the Conditionally Conforming to a Protocol section with information about conditional protocol conformance. - Added information about recursive protocol constraints to the Using a Protocol in Its Associated Type’s Constraints section. - Added information about the canImport() and targetEnvironment() platform conditions to Conditional Compilation Block.