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BurntSushi
go-sumtype
Go2017–2024
BurntSushi / go-sumtype

go-sumtype

A simple utility for running exhaustiveness checks on Go "sum types."

Libraries & SDKs
Explore on GitHubRead Hacker News discussions
10Distinct people
16Mentions
1Explicit recommenders
454GitHub stars
REPOSITORY AT A GLANCE

What to know before exploring

What it is

A simple utility for running exhaustiveness checks on Go "sum types."

GitHub

Where it is used

No documented product use has been verified yet.

What people are saying

The call out to sum types is something I feel. I've been using Rust daily for almost 10 years now, and sum types are absolutely still one of the things I love most about it.…

burntsushi used a recommendation phrase. One indexed comment matches. This is a phrase match, not a verdict.

No classified warning is attached to this page. Read the discussions before treating silence as approval.

Also in these discussions

No other repository is repeatedly linked in the same discussions.

This week on Hacker News

Nov 7–Nov 14 UTC · Direct repository links and separately labeled related project stories. Indexed through 11/14/2026, 3:56:07 PM UTC.

No direct repository links were found in the indexed HN discussions over the past seven days. Older discussions are available below.

Mentions over time

HN mentions by year16 dated mentions

Observed mentions: 2017-03-20 12:11:00 UTC to 2024-11-18 15:00:39 UTC.

012342017-01-01 00:00:00 UTC to 2018-01-01 00:00:00 UTC (exclusive): 4 mentions; 1 submissions, 3 comments20172018-01-01 00:00:00 UTC to 2019-01-01 00:00:00 UTC (exclusive): 2 mentions; 0 submissions, 2 comments2019-01-01 00:00:00 UTC to 2020-01-01 00:00:00 UTC (exclusive): 0 mentions; 0 submissions, 0 comments2020-01-01 00:00:00 UTC to 2021-01-01 00:00:00 UTC (exclusive): 0 mentions; 0 submissions, 0 comments20202021-01-01 00:00:00 UTC to 2022-01-01 00:00:00 UTC (exclusive): 4 mentions; 0 submissions, 4 comments2022-01-01 00:00:00 UTC to 2023-01-01 00:00:00 UTC (exclusive): 3 mentions; 0 submissions, 3 comments2023-01-01 00:00:00 UTC to 2024-01-01 00:00:00 UTC (exclusive): 2 mentions; 0 submissions, 2 comments2024-01-01 00:00:00 UTC to 2025-01-01 00:00:00 UTC (exclusive): 1 mentions; 0 submissions, 1 comments2024

Counts come from the repository’s dated source evidence. Index cutoff: 2026-11-02 08:16:59 UTC.

View mention counts and date ranges
UTC ranges include their start and exclude their end. Select a period to filter the source evidence.
PeriodStart (UTC)End (exclusive, UTC)MentionsSubmissionsComments
20172017-01-01 00:00:00 UTC2018-01-01 00:00:00 UTC413
20182018-01-01 00:00:00 UTC2019-01-01 00:00:00 UTC202
20192019-01-01 00:00:00 UTC2020-01-01 00:00:00 UTC000
20202020-01-01 00:00:00 UTC2021-01-01 00:00:00 UTC000
20212021-01-01 00:00:00 UTC2022-01-01 00:00:00 UTC404
20222022-01-01 00:00:00 UTC2023-01-01 00:00:00 UTC303
20232023-01-01 00:00:00 UTC2024-01-01 00:00:00 UTC202
20242024-01-01 00:00:00 UTC2025-01-01 00:00:00 UTC101

What Hacker News says

16 sources
jerf·Nov 18, 2024
No, you have created "a type that can be one of int, uint, or string, or anything that backs directly to them". They all can >, and since that's the only thing you used in Max, everything works fine. You don't have a sum type; you have "a type that is either an int, a uint, a string, or something that backs to them", specifically. It doesn't come in as any sort of sum type, it is specifically one of those types directly. For one thing, as you've specified it, you don't even have a closed set of types. Off in another package I can declare a "type MyInt int" and use your Max on it, so if you tried to type switch in your Max function, you would not know about my type, and it is arguably the defining characteristic of a sum type that you can know all the branches it has. You can fix that by knocking off the tilde, but then you still have the
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problem that it is not legal to use "switch val := a.(type)", which is basically the level of deconstruction of a type that Go permits, because when the Max function is running, it is not running on a value of type "Ordered"; it literally has a value of the type you passed in. That's the whole point of generics, to have values of the concrete type that was passed in, and not a sort of "sum type". https://go.dev/play/p/MGhRjwvpdTh Note you don't get "Ordered". You get the specific types. That's not any sort of "generic weirdness", that's the real situation. That's why you can only use the intersection of operations they all support. If you want a sum type in Go, use closed interfaces: https://github.com/BurntSushi/go-sumtype If you're willing to accept what you've written as a sum type, you should be even more willing to accept this method, which actually produces a reasonable approximation of one.
In Constraints in Go
jerf·Sep 29, 2023
If you are satisfied with a dummy method on an interface, you can continue by adding more types to that interface. Color is not a great example, so: type Vehicle interface { isVehicle() } type Car struct {} func (c Car) isVehicle() {} type Van struct {} func (v Van) isVehicle() {} func VehicleType(vehicle Vehicle) { switch v := vehicle.(type) { case Car: fmt.Println("car") case Van: fmt.Println("van") default: fmt.Println("unknown vehicle") } This covers most, but not all, of the bases, in that you don't get exhaustiveness checking at compile time, unless you adjoin a linter to your compile process: https://github.com/BurntSushi/go-sumtype
In Compile-time safety for enumerations in Go
burntsushi·Mar 13, 2023Recommendation phrase
The call out to sum types is something I feel. I've been using Rust daily for almost 10 years now, and sum types are absolutely still one of the things I love most about it. It's easily one of the things I miss the most in other languages that don't have them. I'm usually a proponent of "using languages as they're intended," but I missed exhaustiveness checking so much that I ported a version of it to Go[1] as a sort of lint. [1]: https://github.com/BurntSushi/go-sumtype
In Switching from C++ to Rust
burntsushi·Jan 31, 2018
Good post! Crossposting my comment from that other crusty news aggregator: Alternative 1a is to use Alternative 1 with https://github.com/BurntSushi/go-sumtype /plug go-sumtype requires the interface to be sealed (which you're already doing) and one small annotation: //go-sumtype:decl TheInterfaceName Then you just run `go-sumtype` $ go-sumtype $(go list ./... | grep -v vendor) and it will do exhaustiveness checks in any type switch in which `TheInterfaceName` participates. This will prevent the "For example, during a refactor a handler might be removed but a type that implements the interface is not." failure mode mentioned in the article.
In Alternatives to sum types in Go
lobster_johnson·Jan 16, 2018
This looks promising! We use the go-grpc SDK in conjunction with gogoprotobuf, and it's been a rocky road. While the article identifies some operational issues (e.g. the reliance on HTTP/2), there are several considerable deficiencies with gRPC today, at least when using it with Go: 1. The JSON mapping (jsonpb.go) is clumsy at best, and by this I mean that it produces JSON that often doesn't look anything like how you'd hand-design your structures. "oneof" structs, for example, generate an additional level of indirection that you typically wouldn't have. Proto3's decision to forego Proto2's optional values (in Proto3 everything is optional) cause Go's zero value semantics to leak into gRPC [1]. (We had to fork jsonpb.go to fix some of these issues, but as far as I can tell, upstream is still very awkward.) 2. The Go code generator usually
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produces highly unidiomatic Go. "oneof" is yet again an offender here. The gogoprotobuf [2] project tries to fix some of go-grpc's deficiencies, but it's still not sufficient. Ideally you should be able to use the Proto structs directly, but our biggest gRPC project we basically gave up here, and decided to limit Proto usage to the server layer, with a translation layer in between that translates all the Proto structs to/from native structs. That keeps things clean, but it's pretty exhausting work, which lots of type switches (which are hampered by Go's lack of switch exhaustiveness checking; we use BurntSushi's go-sumtype [3] a lot, but I don't think it can work for Proto structs, as it requires that a struct also implements an interface). 3. Proto3 has very limited support for expressing "free-form" data. By this I mean if you need to express a Protobuf field that contains a structured set of data such as {"foo": {"bar": 42}}. For this, you have the extension google.protobuf.Value [4], which supports some basic primitives, but not all (no timestamps, for example) and cannot be used to serialize actual gRPC messages; you can't serialize {"foo": MyProtoMessage{...}}. Free-form structured data is important for systems that accept foreign data where the schema isn't known; for example, a system that indexes analytics data. From what I can tell, though, Twirp doesn't "disrupt" gRPC as much as I'd like, since it appears to rely on the existing JSON mapping. [1] https://github.com/gogo/protobuf/issues/218 [2] https://github.com/gogo/protobuf [3] https://github.com/BurntSushi/go-sumtype [4] https://developers.google.com/protocol-buffers/docs/referenc...
In Twirp: A new RPC framework for Go
atombender·Sep 14, 2017
Not the same as what the article is trying to accomplish, which is an exhaustive match (i.e., any unmatched value is guaranteed to fail at compile time). For example, consider a parser that matches on tokens. If you add a new token, the match should fail, because you want to guarantee, at compile-time, that every possible case is handled. This is one reason that the lack of sum types in Go is so painful, to the point that someone wrote a special library for it [1]. [1] https://github.com/BurntSushi/go-sumtype
In Std::visit is everything wrong with modern C++

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