blog/we-have-go-2: more into generics

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Cadey Ratio 2022-05-06 15:05:54 -04:00
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@ -26,8 +26,8 @@ _catalytic_ to my career goals and its made me into the professional I am
today. Without having met the people I did in the Go slack, I would probably not today. Without having met the people I did in the Go slack, I would probably not
have gotten as lucky as I have as consistently as I have. have gotten as lucky as I have as consistently as I have.
Releasing a “Go 2” has become a philosophical and political challenge due to the Releasing a "Go 2" has become a philosophical and political challenge due to the
forces that be. “Go 2” has kind of gotten the feeling of “this is never going to forces that be. "Go 2" has kind of gotten the feeling of “this is never going to
happen, is it?” with how the political forces within and without the Go team are happen, is it?” with how the political forces within and without the Go team are
functioning. They seem to have been incrementally releasing new features and functioning. They seem to have been incrementally releasing new features and
using version gating in `go.mod` to make it easier on people instead of a big using version gating in `go.mod` to make it easier on people instead of a big
@ -49,7 +49,10 @@ contain my personal feelings or observations about things to these conversation
snippets.</xeblog-conv> snippets.</xeblog-conv>
This is a look back at the huge progress that has been made since Go 1 released This is a look back at the huge progress that has been made since Go 1 released
and what I'd consider to be the headline features of Go 2. and what I'd consider to be the headline features of Go 2. Most of this is a
whirlwind tour of over a half-decade of improvments to the Go compiler, toolchain
and standard library. I highly encourage you read this fairly large post in chunks
because it will feel like _a lot_ if you read it all at once.
## The Compiler Rewrite in Go ## The Compiler Rewrite in Go
@ -447,6 +450,8 @@ select {
} }
``` ```
### Package `context`
However if your stop channel was a `chan bool` and you relied on the `bool` However if your stop channel was a `chan bool` and you relied on the `bool`
value being `true`, this would fail because the value would be `false`. This value being `true`, this would fail because the value would be `false`. This
was a bit too brittle for comfortable widespread production use and we ended was a bit too brittle for comfortable widespread production use and we ended
@ -660,15 +665,87 @@ an `io.Writer` that automatically encrypts everything you feed It with TLS, or
even something like sending data over a Unix socket instead of a TCP one. If it even something like sending data over a Unix socket instead of a TCP one. If it
fits the shape of the interface, it Just Works. fits the shape of the interface, it Just Works.
- [ ] Show where that falls apart However, this falls apart when you want to deal with a collection of _only one_
- [ ] The container package type that meets an interface at once. When you create a slice of `Quacker`s and
- [ ] Cloner pass it to a function, you can put both `Duck`s and `Sheep` into that slice:
- [ ] Viewer
- [ ] Introduce Go generics ```go
- [ ] Overview of some of the types of collections it lets you make quackers := []Quacker{
- [ ] Take a function with a slice `Duck`s or a slice of `Sheep` but not Duck{},
mixed `Duck`s and `Sheep` Sheep{},
- [ ] This is a huge improvement to the language }
doSomething(quackers)
```
If you want to assert that every `Quacker` is the same type, you have to do some
fairly brittle things that step around Go's type safety like this:
```go
func doSomething(qs []Quacker) error {
// Store the name of the type of first Quacker.
// We have to use the name `typ` because `type` is
// a reserved keyword.
typ := fmt.Sprintf("%T", qs[0])
for i, q := range qs {
if qType := fmt.Sprintf("%T", q); qType != typ {
return fmt.Errorf("slice value %d was type %s, wanted: %s", qType, typ)
}
q.Quack()
}
return nil
}
```
This would explode at runtime. This same kind of weakness is basically the main
reason why the Go standard library package [`container`](https://pkg.go.dev/container)
is mostly unused. Everything in the `container` package deals with
`interface{}`/`any` values, which is Go for "literally anything". This means
that without careful wrapper code you need to either make interfaces around
everything in your lists (and then pay the cost of boxing everything in an
interface, which adds up a lot in practice in more ways than you'd think) or
have to type-assert anything going into or coming out of the list, combined
with having to pay super close attention to anything touching that code
during reviews.
<xeblog-conv name="Cadey" mood="enby">Don't get me wrong, interface types
are an _amazing_ standout feature of Go. They are one of the main reasons that
Go code is so easy to reason about and work with. You don't have to worry
about the entire tree of stuff that a value is made out of, you can just
assert that values have behaviors and then you're off to the races. I end up
missing the brutal simplicity of Go interfaces in other languages like Rust.
</xeblog-conv>
### Introducing Go Generics
In Go 1.18, support for adding types as parameters to other types was added.
This allows you to define constraints on what types are accepted by a function,
so that you can reuse the same logic for multiple different kinds of underlying
types or write collections that deal with values of a given type that meets an
interface without also having to make sure that everything else in that
collection is of the same type at runtime.
That `doSomething` function from above could be rewritten like this with
generics:
```go
func doSomething[T Quacker](qs []T) {
for i, q := range qs {
q.Quack()
}
}
```
We can totally refactor out the error return and any of that runtime fallible
code. This allows us to express constraints at _compile time_ so that
attempting to mix `Duck`s and `Sheep` in the same argument to `doSomething`
will fail to build.
- [ ] Overview of some of the types of collections it lets you make
- [ ] This is a huge improvement to the language
--- ---