[gardening][(JSON|Plist)Encoder] Prefer !isEmpty over count > 0

[ikesyo]

No description provided.

[ikesyo]

@swift-ci Please smoke test

[ikesyo]

@swift-ci smoke test

[ikesyo]

The failure looks unrelated.

@swift-ci Please clean smoke test Linux platform

[itaiferber]

Thanks for taking the time to put this together; the change itself looks okay, but is there a concrete reason for the code churn?

[ikesyo]

@itaiferber I'm a fan of using isEmpty over checking count as described in the doc comments of Collection.count:

  /// The number of elements in the collection.
  ///
  /// To check whether a collection is empty, use its `isEmpty` property
  /// instead of comparing `count` to zero. Unless the collection guarantees
  /// random-access performance, calculating `count` can be an O(*n*)
  /// operation.
  ///
  /// - Complexity: O(1) if the collection conforms to
  ///   `RandomAccessCollection`; otherwise, O(*n*), where *n* is the length
  ///   of the collection.
  var count: Int { get }

Or the doc comments is not right or is misleading? Is that only about count == 0 case and not about count > 0?

For the cases in this PR the collections are random-access ones so there should be no differences actually, but using isEmpty consistently would be a good habit I think.

[ikesyo]

Ref: #15326

[ikesyo]

See also #12504 (comment) and #12638.

[ikesyo]

Please let me know if I have overlooked something 😃

[harlanhaskins]

@itaiferber At the very least, changing the instance of stringKey.count > 0 in _convertToSnakeCase is taking it from an O(n) operation to an O(1) operation.

[itaiferber]

From a correctness perspective, I don't disagree — it's just that our collections offer O(1) count and JSON keys are rarely long (and overwhelmingly often ASCII), so O(n) vs. O(1) won't make much of a difference there. Just trying to find a balance between correctness and code churn.

[itaiferber]

Please make a similar change over on https://github.com/apple/swift-corelibs-foundation, if you don't mind.