On Mon, May 3, 2021 at 4:39 PM 'Axel Wagner' via golang-nuts
<golang-nuts@googlegroups.com> wrote:
>
> this thread had me wonder again about a spec question that recently came up
> which I didn't have an answer to: Where does the spec say, which recursive
> type declarations are allowed and which aren't? For example, why is `type T
> *T` legal, but `type T T`ยน isn't?
>
> To be clear: I know why we can't make `type T T` et al. legal - the compiler
> needs to know the size of the values and it can't know it from a declaration
> like `type T T`. I'm wondering how this follows from the spec.
>
> I haven't read through all of the spec in a while, so I might just be missing
> an obvious section. But it doesn't seem to be described in the section about
> type declarations and some obvious keyword searches like "recursive" or
> "size" didn't turn up anything meaningful, as far as I can tell. But feel
> free to point me to a section I overlooked, and apologies if the question
> makes me seem lazy because it ends up being obvious :)
>
> [1] Maybe `type T struct { T }` is a better example, as it's a type-literal,
> not a type name - just like `type T *T`.
I think you are correct that this is not explicitly defined anywhere.
The basic rule is fairly straightforward: a type definition can't
contain or embed an instance of itself, but it can otherwise refer to
itself. But that ought to be in the spec, and as far as I know it is
not.
Ian
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