[go-nuts] Type tags, in addition to struct (field) tags?

Tags were put in to support transport metadata for structs, to avoid
needed an external IDL for JSON, XML, protocol buffers and so on. They
have indeed been useful but they also result in noisy-looking code and
encourage a weak and clumsy kind of metaprogramming. It's telling that
they're only visible through the reflection interface.

I would be reluctant to extend their reach.

-rob

If you're already parsing Go code, you can use comments for that kind of thing:

//gen thing
type Thing struct { ... }


gustavo @ http://niemeyer.net

I had this same requirement for my codec library and I solved it by
defining a private field within the struct and assigning tags to it. E.g.

type Thing struct {
   __struct struct{} `tag:"thing"`
   Field1 int
}

This works well for me. It's unexported, so you don't lose anything.

Ugorji, that's an interesting approach, may try that.

Rob, thanks for the explanation. Good point about arbitrary text morphing
into a bad programming language.

- Matt

If we pretend that the proposal (and proposed syntax) were universally
favored, it'd result in an inconsistent grammar. Consider:

// the brace must go on the same line as the tag

In the above, the tag in the struct case goes after the struct keyword. For
primitive types, it'd Go after the type definition. Really, the only
consistent approach is to put the tag after the entire type definition, and
that'd result in:

type Thing struct {

That looks a bit like typedef's in C, and typedef'd structs are pretty ugly.

I went with the comment approach here, seems to
work: http://clipperhouse.github.io/gen/#Subsetting