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points by awesome_dude 3 days ago | 0 comments
I'm confused by this - you're saying that a "type system" would address this, even though there are two (incompatible) type systems at play here - Go's and JSON's

Compile time cannot check for runtime values (not even in Rust) - is your position that fields can only be populated at compile time?

[–] thayne 3 days ago
In go, the Marshall and unmarshal functions take `any` for the source or destination. If you use a value of a type that doesn't support marshaling or unmarshalling (say because it contains an unserializable type like a channel, function pointer, etc) then you get a runtime error. Whereas in rust, Haskell, scala, etc. you can get a compile time error if you try to use a type that doesn't support serialization.
[–] hnlmorg 3 days ago
You don’t get runtime errors for marshalling pointers to JSON. I actually do this all the time. What you get is the address of the pointer marshalled.

I think the same is true for channels too but I’m not near a computer to check.

I’ve abused the v1 API heavily* and haven’t found anything it couldn’t marshal. Though I’m yet to apply the same “fuzzing” (for lack of a better term) to v2.

* the v1 JSON marshaller underpins some core functionality in my alternative $SHELL. So I’ve thrown a lot of exotic type structures (by Gos standards at least) at it.

[–] thayne 2 days ago
> You don’t get runtime errors for marshalling pointers to JSON

https://pkg.go.dev/encoding/json/v2#Marshal says otherwise:

> The Go map key must encode as a JSON string, otherwise this results in a SemanticError

> All other Go types (e.g., complex numbers, channels, and functions) have no default representation and result in a SemanticError.

v1 has the same constraints.

[–] hnlmorg 2 days ago
> A Go pointer is encoded as a JSON null if nil, otherwise it is the recursively JSON-encoded representation of the underlying value.

The doc you linked to literally proves me right.

[–] thayne 2 days ago
That just shows there are pointer values that can be marshaled, not that all such values won't error. If you have a non-nil pointer that points to an object that transitively contains one of the unsupported types, you will get an error.
[–] hnlmorg 2 days ago
I read that differently. If you have a non-nil pointer then you get the address of the pointer irrespective of what that pointer points too.
[–] thayne 1 day ago
I'm not sure how you are getting that from "otherwise it is the recursively JSON-encoded representation of the underlying value", but here is a playground example, where using a non-nil pointer to a channel produces an error: https://go.dev/play/p/JXYuGUQ0TLQ