encoding/binary: can't compare NativeEndian with LittleEndian/BigEndian

[dolmen]

TL;DR: binary.NativeEndian == binary.BigEndian doesn't work.

Follow-up on #57237.

What version of Go are you using (go version)?

$ go version
go version go1.21.3 darwin/amd64

Does this issue reproduce with the latest release?

Yes.

What did you do?

https://go.dev/play/p/PIdcmG89Rp-

package main

import (
	"encoding/binary"
	"fmt"
)

func main() {
	fmt.Println(binary.NativeEndian == binary.BigEndian)
}

What did you expect to see?

I expect this program to compile and to allow me to simply determine if the platform is big endian or little endian as a boolean value.

As the author of package github.com/dolmen-go/endian which provided Native long before and has this feature, I miss that.

What did you see instead?

./prog.go:9:37: invalid operation: binary.NativeEndian == binary.BigEndian (mismatched types binary.nativeEndian and binary.bigEndian)

[bcmills]

Programs generally shouldn't need to care which endianness is native, especially if they are already using encoding/binary. But for the rare ones that do, how about golang.org/x/sys/cpu.IsBigEndian?

[rittneje]

From what I recall, this is an artifact of the fact that binary.LittleEndian and binary.BigEndian are not comparable with each other. So if for example binary.NativeEndian were an alias of binary.LittleEndian on a little endian system, then binary.NativeEndian == binary.LittleEndian would return true on little endian and fail to compile on big endian. The only way around that would have been to make binary.NativeEndian an interface, preventing some compile-time optimizations.

I'll note your library has the compilation issue I mentioned, so I don't think it can be used in the way you intended. https://go.dev/play/p/NuQV5ijf5PG

[cagedmantis]

cc @griesemer