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Comment by kbolino | Hacker News Reader

This feels like a style complaint and not one about substance. An inaccessible (because it's named _) zero-length struct field is just another kind of metadata. It also doesn't require you to pollute the method set, which would be a bigger issue.

The real hack to me is that anything which simply has Lock() and Unlock() methods is considered uncopyable.

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Coming from Rust anyway (can't say I'm familiar with Go), nothing about having it as a trait would pollute the method set, traits don't have to have methods (e.g. pin, unpin, send, sync, etc.). Yes a zero length field can be metadata and this is a style complaint but a struct's fields are traditionally its data and the type is its metadata, I feel like it's harmful to mix these two as I at least wouldn't generally look at fields to find metadata for the struct.

Interfaces in Go (the closest equivalent to traits in Rust) don't have to have methods either, but they are structurally typed. This is like "static duck typing" if you will. So an interface with no methods is implemented by every type in the language (indeed, this became such a useful pattern that the name "any" was reserved for it in Go 1.18).

Marker interfaces can exist in Go, but here they are another kind of hack. They must define at least one method (which doesn't have to be public), though that method is never actually meant to be called.

I'm only peripherally familiar with Go. IIRC, Rust defaults to move-only structs with the option to make them copyable with the Copy trait. Swift defaults to copyable structs (like Go), but has a ~Copyable generic type constraint to make them move-only.

Rust has similar zero-sized-types, probably the most 'magical' being PhantomData.

> The real hack to me is that anything which simply has Lock() and Unlock() methods is considered uncopyable.

It's a shame they made them generic, taking no arguments and returning nothing; if they'd gone for `Lock(sync.LockType)` or something like that, it would be more difficult to accidentally trigger the `noCopy` flag.

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