即contains操作

  /// - Parameter member: An element to look for in the set.

  /// - Returns: `true` if `member` exists in the set; otherwise, `false`.

  ///

  /// - Complexity: O(1)

  @inlinable

  public func contains(_ member: Element) -> Bool {

    return _variant.contains(member)

  }

最终走到了 _NativeSet 的逻辑。


  /// Search for a given element, assuming it has the specified hash value.

  ///

  /// If the element is not present in this set, return the position where it

  /// could be inserted.

  @inlinable

  @inline(__always)

  internal func find(

    _ element: Element,

    hashValue: Int

  ) -> (bucket: Bucket, found: Bool) {

    let hashTable = self.hashTable

    var bucket = hashTable.idealBucket(forHashValue: hashValue)

    while hashTable._isOccupied(bucket) {

      if uncheckedElement(at: bucket) == element {

        return (bucket, true)

      }

      bucket = hashTable.bucket(wrappedAfter: bucket)

    }

    return (bucket, false)

  }