Hello Swift Community,
The review of SE-0154 "Provide Custom Collections for Dictionary Keys and Values” ran from February 17…22, 2017. The proposal is accepted into Swift 4. Feedback was generally positive, and the core team felt that this proposal was a useful step forward for Dictionary, providing more flexibility for the standard library ABI and better performance. However, the core team noted that acceptance of this proposal should not preclude improvements to the ergonomics of Dictionary, even for the use cases described in the proposal itself (e.g., inserting an empty collection if it isn’t already there, and appending a value to the collection).