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Go 2, here we come!

29 November 2018

Background

At GopherCon 2017, Russ Cox officially started the thought process on the

next big version of Go with his talk The Future of Go

(blog post). We have

called this language informally Go 2, even though we understand now

that it will arrive in incremental rather than with a big bang and a

single release. Still, Go 2 is a useful moniker, if only to have a way

to talk about that future language, so let’s keep using it for now.

A major difference between Go 1 and Go 2 is who is going to influence the

design and how decisions are made. Go 1 was a small team effort with modest

outside influence; Go 2 will be much more community-driven.

After almost years of exposure, we have

learned a lot about the language and libraries that we didn’t know in the

beginning, and that was only possible through feedback from the Go community.

In 2015 we introduced the proposal process

to gather a specific kind of feedback: proposals for language and library

changes. A committee composed of senior Go team members has been reviewing,

categorizing, and deciding on incoming proposals on a regular basis. That

has worked pretty well, but as part of that process we have ignored all

proposals that are not backward-compatible, simply labeling them Go 2 instead.

In 2017 we also stopped making any kind of incremental backward-compatible

language changes, however small, in favor of a more comprehensive plan that

takes the bigger picture of Go 2 into account.

It is now to act on the Go 2 proposals, but to do this we first need a plan.

Status

At the time of writing, there are around 120

open issues labeled Go 2 proposal.

Each of them proposes a significant library or language change, often one

that does not satisfy the existing

Go 1 compatibility guarantee.

Ian Lance Taylor and I

have been working through these proposals and categorized them

(Go2Cleanup,

NeedsDecision,

etc.) to get an idea of what’s there and to make it easier to

proceed with them. We also merged related proposals and closed the ones which

seemed clearly out of the scope of Go, or were otherwise unactionable.

Ideas from the remaining proposals will likely influence Go 2’s libraries

and languages. Two major themes have emerged early on: support for better

error handling, and generics. Draft designs

for these two areas have been

published at this year’s GopherCon, and more exploration is needed.

But what about the rest? We are constrained

by the fact that we now have

millions of Go programmers and a large body of Go code, and we need to

bring it all along, lest we risk a split ecosystem. That means we cannot

make many changes, and the changes we are going to make need to be chosen

carefully. To make progress, we are implementing a new proposal evaluation

process for these significant potential changes.

Proposal evaluation process

The purpose of the proposal evaluation process is to collect feedback on

a small number of select proposals such that a final decision can be made.

The process runs more or less in parallel to a release cycle and consists

of the following steps:

1. Proposal selection. The Go team selects a small number of

Go 2 proposals

that seem worth considering for acceptance, without making a final decision.

See below for more on the selection criteria.

2. Proposal feedback. The Go team sends out an announcement listing the selected

proposals. The announcement explains to the community the tentative intent to

move forward with the selected proposals and to collect feedback for each

of them. This gives the community a chance to make suggestions and express

concerns.

3. Implementation. Based on that feedback, the proposals are implemented.

The target for these significant language and library changes is to have

them to submit on day 1 of an upcoming release cycle.

4. Implementation feedback. During the development cycle, the Go team and

community have a chance to experiment with the new features and collect

further feedback.

5. Launch decision. At the end of the three month

development cycle

(just when starting the three month repo freeze before a release), and

based on the experience and feedback gathered during the release cycle,

the Go team makes the final decision about whether to ship each change.

This provides an opportunity to consider whether the change has delivered

the expected benefits or created any unexpected costs. Once shipped, the

changes become part of the language and libraries. Excluded proposals may

go back to the drawing board or may be declined for good.

With two rounds of feedback, this process is slanted towards declining

proposals, which will hopefully prevent feature creep and help with

keeping the language small and clean.

We can’t go through this process for each of the open Go 2

proposals, there are simply too many of them. That’s where the selection

criteria come into play.

Proposal selection criteria

A proposal must at the very least:

1. address an important issue for many people,

2. have minimal impact on everybody else, and

3. come with a clear and well-understood solution.

Requirement 1 ensures that any changes we make help as many Go developers

as possible (make their code more robust, easier to write, more likely to

be correct, and so on), while requirement 2 ensures we are careful to hurt

as few developers as possible, whether by breaking their programs or causing

other churn. As a rule of thumb, we should aim to help at least ten times as

many developers as we hurt with a given change. Changes that don’t affect

Go usage are a net zero benefit put up against a significant

implementation cost and should be avoided.

Without requirement 3 we don’t have an implementation of the proposal.

For instance, we believe that some form of genericity might solve an important

issue for a lot of people, but we don’t yet have a clear and well-understood

solution. That’s fine, it just means that the proposal needs to go back to

the drawing board before it can be considered.

Proposals

We feel that this is a good plan that should serve us well but it is important

to understand that this is only a starting point. As the process is used we will

discover the ways in which it fails to work well and we will refine it as needed.

The critical part is that until we use it in practice we won’t know how to it.

A safe place to start is with a small number of backward-compatible language

proposals. We haven’t done language changes for a long time, so this gets us

back into that mode. Also, the changes won’t require us worrying about

breaking existing code, and thus they serve as a perfect trial balloon.

With all that said, we propose the following selection of Go 2 proposals for

the Go 1.13 release (step 1 in the proposal evaluation process):

1. #20706 General Unicode identifiers based on Unicode TR31:

This addresses an important issue for Go programmers using non-Western alphabets

and should have little if any impact on anyone else. There are normalization

questions which we need to answer and where community feedback will be

important, but after that the implementation path is well understood.

Note that identifier export rules will not be affected by this.

2. #19308, #28493 Binary integer literals and support for_ in number literals:

These are relatively minor changes that seem hugely popular among many

programmers. They may not quite reach the threshold of solving an

“important issue” (hexadecimal numbers have worked well so far) but they

bring Go up to par with most other languages in this respect and relieve

a pain point for some programmers. They have minimal impact on others who

don’t care about binary integer literals or number formatting, and the

implementation is well understood.

3. #19113 Permit signed integers as shift counts:

An estimated 38% of all non-constant shifts require an (artificial) uint

conversion (see the issue for a more detailed break-down). This proposal

will clean up a lot of code, get shift expressions better in sync with index

expressions and the built-in functions cap and len. It will mostly have a

positive impact on code. The implementation is well understood.

Next steps

With this post we have executed the first step and started the second

step of the proposal evaluation process. It’s now up to you, the

Go community, to provide feedback on the issues listed above.

For each proposal for which we have clear and approving feedback, we will

move forward with the implementation (step 3 in the process). Because we

want the changes implemented on the first day of the next release cycle

(tentatively Feb. 1, 2019) we may start the implementation a bit early

this time to leave time for two full months of feedback (Dec. 2018,

Jan. 2019).

For the 3-month development cycle (Feb. to May 2019) the chosen features

are implemented and available at tip and everybody will have a chance to

gather experience with them. This provides another opportunity for feedback

(step 4 in the process).

Finally, shortly after the repo freeze (May 1, 2019), the Go team makes the

final decision whether to keep the new features for good (and include them

in the Go 1 compatibility guarantee), or whether to abandon them (final

step in the process).

(Since there is a real chance that a feature may need to be removed just

when we freeze the repo, the implementation will need to be such that the

feature can be disabled without destabilizing the rest of the system.

For language changes that may mean that all feature-related code is

guarded by an internal flag.)

This will be the first time that we have followed this process, hence the

repo freeze will also be a good moment to reflect on the process and to

adjust it if necessary. Let’s see how it goes.

Happy evaluating!

By Robert Griesemer



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