[Review] SE-0154: Provide Custom Collections for Dictionary Keys and Values

Douglas_Gregor · 2017-02-18T00:12:16.000Z

Hello Swift community,

The review of SE-0154 "Provide Custom Collections for Dictionary Keys and Values" begins now and runs through February 22, 2017. The proposal is available here:

github.com

apple/swift-evolution/blob/master/proposals/0154-dictionary-key-and-value-collections.md

# Provide Custom Collections for Dictionary Keys and Values

* Proposal: [SE-0154](0154-dictionary-key-and-value-collections.md)
* Author: [Nate Cook](https://github.com/natecook1000)
* Review Manager: [Doug Gregor](https://github.com/DougGregor)
* Status: **Implemented (Swift 4)**
* Decision Notes: [Rationale](https://lists.swift.org/pipermail/swift-evolution/Week-of-Mon-20170220/033159.html)

## Introduction

This proposal addresses significant unexpected performance gaps when using dictionaries. It introduces type-specific collections for a `Dictionary` instance's `keys` and `values` properties.

New collection types provide efficient key lookup and mutable access to dictionary values, allowing in-place updates and copy-on-write optimization of stored values. The addition of these new types impacts the standard library ABI, since we won't be able to use types aliases from the existing types for `keys` and `values`.

Swift-evolution thread: [[Proposal Draft] Provide Custom Collections for Dictionary Keys and Values](https://lists.swift.org/pipermail/swift-evolution/Week-of-Mon-20161010/027815.html)


## Motivation

This proposal address two problems:

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Reviews are an important part of the Swift evolution process. All reviews should be sent to the swift-evolution mailing list at

https://lists.swift.org/mailman/listinfo/swift-evolution
or, if you would like to keep your feedback private, directly to the review manager. When replying, please try to keep the proposal link at the top of the message:

Proposal link:

github.com

apple/swift-evolution/blob/master/proposals/0154-dictionary-key-and-value-collections.md

# Provide Custom Collections for Dictionary Keys and Values

* Proposal: [SE-0154](0154-dictionary-key-and-value-collections.md)
* Author: [Nate Cook](https://github.com/natecook1000)
* Review Manager: [Doug Gregor](https://github.com/DougGregor)
* Status: **Implemented (Swift 4)**
* Decision Notes: [Rationale](https://lists.swift.org/pipermail/swift-evolution/Week-of-Mon-20170220/033159.html)

## Introduction

This proposal addresses significant unexpected performance gaps when using dictionaries. It introduces type-specific collections for a `Dictionary` instance's `keys` and `values` properties.

New collection types provide efficient key lookup and mutable access to dictionary values, allowing in-place updates and copy-on-write optimization of stored values. The addition of these new types impacts the standard library ABI, since we won't be able to use types aliases from the existing types for `keys` and `values`.

Swift-evolution thread: [[Proposal Draft] Provide Custom Collections for Dictionary Keys and Values](https://lists.swift.org/pipermail/swift-evolution/Week-of-Mon-20161010/027815.html)


## Motivation

This proposal address two problems:

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<Pull requests · apple/swift-evolution · GitHub goes into a review?

The goal of the review process is to improve the proposal under review through constructive criticism and, eventually, determine the direction of Swift. When writing your review, here are some questions you might want to answer in your review:

What is your evaluation of the proposal?
Is the problem being addressed significant enough to warrant a change to Swift?
Does this proposal fit well with the feel and direction of Swift?
If you have used other languages or libraries with a similar feature, how do you feel that this proposal compares to those?
How much effort did you put into your review? A glance, a quick reading, or an in-depth study?
More information about the Swift evolution process is available at

github.com

apple/swift-evolution/blob/master/process.md

# Swift Evolution Process

Swift is a powerful and intuitive programming language that is designed to make writing and maintaining correct programs easier. Swift is growing and evolving, guided by a community-driven process referred to as the Swift evolution process. This document outlines the Swift evolution process and how a feature grows from a rough idea into something that can improve the Swift development experience for millions of programmers.

## Scope

The Swift evolution process covers all changes to the Swift language and the public interface of the Swift standard library, including new language features and APIs (no matter how small), changes to existing language features or APIs, removal of existing features, and so on. Smaller changes, such as bug fixes, optimizations, or diagnostic improvements can be contributed via the normal contribution process; see [Contributing to Swift](https://swift.org/community/#contributing).

## Goals

The Swift evolution process aims to leverage the collective ideas, insights, and experience of the Swift community to improve the Swift development experience. Its two primary goals are:

* Engage the wider Swift community in the ongoing evolution of Swift, and
* Maintain the vision and conceptual coherence of Swift.

There is a natural tension between these two goals. Open evolution processes are, by nature, chaotic. Yet, maintaining a coherent vision for something as complicated as a programming language requires some level of coordination. The Swift evolution process aims to strike a balance that best serves the Swift community as a whole.

## Participation

Everyone is welcome to propose, discuss, and review ideas to improve

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Thank you,

-Doug Gregor

Review Manager

DevAndArtist · 2017-02-18T00:20:17.000Z

What is your evaluation of the proposal?

This is welcome improvement.

Is the problem being addressed significant enough to warrant a change to Swift?

Definitely.

Does this proposal fit well with the feel and direction of Swift?

It does indeed.

If you have used other languages or libraries with a similar feature, how do you feel that this proposal compares to those?

I can’t think of an example to compare with.

How much effort did you put into your review? A glance, a quick reading, or an in-depth study?

Carefully read the whole proposal and took part in discussions involving the proposed solution.

anandabits · 2017-02-18T16:10:21.000Z

What is your evaluation of the proposal?

+1.

Is the problem being addressed significant enough to warrant a change to Swift?

Yes

Does this proposal fit well with the feel and direction of Swift?

Yes

If you have used other languages or libraries with a similar feature, how do you feel that this proposal compares to those?

N/A

How much effort did you put into your review? A glance, a quick reading, or an in-depth study?

A quick read.

tali · 2017-02-18T20:35:15.000Z

The review of SE-0154 "Provide Custom Collections for Dictionary Keys and Values" begins now and runs through February 22, 2017. The proposal is available here:

https://github.com/apple/swift-evolution/blob/master/proposals/0154-dictionary-key-and-value-collections.md

I haven’t followed the discussion too closely, so I’m sorry if this has already been answered:
What’s the rationale for selecting this proposal over the alternatives?
Especially with the upcoming Ownership Manifesto, value mutation may be solved much more easily.
Should we invest some more time into exploring the `modify` declaration for dictionaries?

— Martin

Scott_James_Remnant · 2017-02-19T18:21:29.000Z

This proposal directly addresses one of my least favorite patterns in Swift.

It's a good improvement and I would be content with it being accepted as-is.

However I do still feel that the solution is "clunky," and that being able to mutate a dictionary entry via the Optional would be much cleaner code.

···

Sent from my iPad

On Feb 17, 2017, at 7:12 PM, Douglas Gregor <dgregor@apple.com> wrote:

Hello Swift community,

The review of SE-0154 "Provide Custom Collections for Dictionary Keys and Values" begins now and runs through February 22, 2017. The proposal is available here:

https://github.com/apple/swift-evolution/blob/master/proposals/0154-dictionary-key-and-value-collections.md
Reviews are an important part of the Swift evolution process. All reviews should be sent to the swift-evolution mailing list at

https://lists.swift.org/mailman/listinfo/swift-evolution
or, if you would like to keep your feedback private, directly to the review manager. When replying, please try to keep the proposal link at the top of the message:

Proposal link:

https://github.com/apple/swift-evolution/blob/master/proposals/0154-dictionary-key-and-value-collections.md
Reply text

Other replies
What goes into a review?

The goal of the review process is to improve the proposal under review through constructive criticism and, eventually, determine the direction of Swift. When writing your review, here are some questions you might want to answer in your review:

What is your evaluation of the proposal?
Is the problem being addressed significant enough to warrant a change to Swift?
Does this proposal fit well with the feel and direction of Swift?
If you have used other languages or libraries with a similar feature, how do you feel that this proposal compares to those?
How much effort did you put into your review? A glance, a quick reading, or an in-depth study?
More information about the Swift evolution process is available at

https://github.com/apple/swift-evolution/blob/master/process.md
Thank you,

-Doug Gregor

Review Manager

_______________________________________________
swift-evolution-announce mailing list
swift-evolution-announce@swift.org
https://lists.swift.org/mailman/listinfo/swift-evolution-announce

hlovatt · 2017-02-21T23:19:21.000Z

The review of SE-0154 "Provide Custom Collections for Dictionary Keys and
Values" begins now and runs through February 22, 2017. The proposal is
available here:

https://github.com/apple/swift-evolution/blob/master/proposals/0154-dictionary-key-and-value-collections.md

- What is your evaluation of the proposal?

Good idea. A good compromise between backward compatibility and usability.

- Is the problem being addressed significant enough to warrant a
change to Swift?

Yes

- Does this proposal fit well with the feel and direction of Swift?

Yes

- If you have used other languages or libraries with a similar
feature, how do you feel that this proposal compares to those?

Yes, I have found other dictionary implementations more performance and

more flexible (e.g. Java's Map)

···

- How much effort did you put into your review? A glance, a quick
reading, or an in-depth study?

Quick glance

--
-- Howard.

Alvae · 2017-02-19T21:14:30.000Z

What is your evaluation of the proposal?

+1

Nevertheless it’s a bit unclear to me what is the impact of these additional collections on the ownership of the dictionary.

Is the problem being addressed significant enough to warrant a change to Swift?

Yes.

If you have used other languages or libraries with a similar feature, how do you feel that this proposal compares to those?

Python 3 addressed this issue (w.r.t Python 2) in a similar way, using dict_[keys|values] objects. It is common in that language to manipulate the dict_keys. As they are set-like structures, it allows to efficiently manipulate the keys of a dictionary prior to its access/modification.
The proposal doesn’t elaborate on the use of

I feel like the proposal’s Dictionary.Keys could benefit from a similar approach, not limiting itself to conforming to Collection.

How much effort did you put into your review? A glance, a quick reading, or an in-depth study?

A careful reading.