And in terms of practical advice:
You might be able to use go:linkname yourself to get access to that
functionality from the runtime. But note that go:linkname is being locked
down in Go 1.23 <https://github.com/golang/go/issues/67401>, so that is not
a future-proof plan.
Your best bet is probably to file a proposal to get the functionality you
want for strings.Builder. Or to get an exported API (say in the runtime
package) to allocate non-zeroed memory.
Otherwise, you might be able to use `unsafe` to access the unexported
fields of `strings.Builder`. That is, you can define your type as
type MyBuilder struct {
strings.Builder
}
and then add methods to that which use `unsafe` to do what you want. Though
that will, of course, also be dangerous and should be guarded with build
tags for the used Go version, at the least.
On Wed, 26 Jun 2024 at 08:46, Axel Wagner <axel.wagner...@googlemail.com>
wrote:
> It is defined in the runtime and go:linkname'd into the bytealg package:
>
> https://github.com/golang/go/blob/90bcc552c0347948166817a602f612f219bc980c/src/runtime/slice.go#L394
>
> From the spec <https://go.dev/ref/spec#Function_declarations>:
>
>> A function declaration without type parameters may omit the body. Such a
>> declaration provides the signature for a function implemented outside Go,
>> such as an assembly routine
>
>
> How that works is, of course, implementation defined. It may be using
> assembly or, as in this case, with the body being provided by the linker
> later.
>
> On Wed, 26 Jun 2024 at 08:38, Mike Schinkel <m...@newclarity.net> wrote:
>
>> Can someone help me understand how `bytealg.MakeNoZero()` in the Go
>> standard library works, please?
>>
>>
>> https://github.com/golang/go/blob/master/src/internal/bytealg/bytealg.go#L118
>>
>> In the source it is a `func` without a body, and in my own code that
>> won't compile in Go; I get "missing function body." Where is its
>> implementation and how does the Go compiler handle it?
>>
>> I discovered `bytealg.MakeNoZero()` looking into the source for
>> `strings.Builder`:
>>
>> https://github.com/golang/go/blob/master/src/strings/builder.go#L61
>>
>> I was considering following the advice in Go Proverbs that "A little
>> copying is better than a little dependency" but I obviously found that I
>> cannot copy it to my own package and compile it, at least not as-is.
>>
>> I wanted to create my own version of `strings.Builder` that has a
>> `Rewind()` method to allow slicing one or more characters from the internal
>> `buf` buffer, e.g.:
>>
>> https://github.com/golang/go/blob/master/src/strings/builder.go#L23
>>
>> func (b *StringBuilder) Rewind(n int) {
>> if n > len(b.buf) {
>> n = len(b.buf)
>> }
>> b.buf = b.buf[:len(b.buf)-n]
>> }
>>
>> I could of course modify the code of `strings.Builder` to replace
>> `bytealg.MakeNoZero()` but then I would have a less performant string
>> builder, especially for larger strings:
>>
>>
>> https://github.com/golang/go/commit/132fae93b789ce512068ff4300c665b40635b74e
>>
>> Any insight into `bytealg.MakeNoZero()` would be appreciated.
>>
>> -Mike
>>
>> --
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>>
>
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