Resolve SwiftLint errors

[woxtu]

Hi,

This PR resolves the following SwiftLint errors:

Identifier Name Violation: Variable name 'i' should be between 3 and 40 characters long (identifier_name)
Large Tuple Violation: Tuples should have at most 2 members (large_tuple)
Force Cast Violation: Force casts should be avoided (force_cast)
Line Length Violation: Line should be 200 characters or less; currently it has 221 characters (line_length)

[guoyingtao]

Thanks for the PR. Looks good!