feat: support class_s4

[JosiahParry]

I would like to create an S7 class where one of the properties is a DBI SQLiteConnection which is an S4 object.

At present this is only possible by using a class_any

[lawremi]

There is direct compatibility with S4 classes. Just use the S4 class object, returned from getClass(), as the type for your property. I'm pretty sure this is already well documented, but perhaps not obvious enough.

[JosiahParry]

I'm not sure what you mean by that to be honest 😅 how do i make the S4 class object a property of an S7 object?

[lawremi]

Use it as the class for your property

…

On Sun, Jan 11, 2026, 6:21 PM Josiah Parry ***@***.***> wrote: *JosiahParry* left a comment (RConsortium/S7#587) <#587 (comment)> I'm not sure what you mean by that to be honest 😅 how do i make the S4 class object a property of an S7 object? — Reply to this email directly, view it on GitHub <#587 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AABGT3VMGUMDOFHNB6R5Q334GMALFAVCNFSM6AAAAACRJLXOM6VHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHMZTOMZWGY3TCOJQHA> . You are receiving this because you commented.Message ID: ***@***.***>

[JosiahParry]

Sorry, I'm feeling quite daft. Here's a repro:

library(S7)

# Doesn't work
new_class(
  "Foo",
  properties = list(
    id = class_character,
    # Would like a class_s4 here
    db = DBI::dbConnect(RSQLite::SQLite())
  )
)
#> Error: Can't convert `property$db` to a valid class. Unsupported S4 object: must be a class generator or a class definition, not a S4<SQLiteConnection>.

# DOoes work
new_class(
  "Foo",
  properties = list(
    id = class_character,
    db = class_any
  ),
  validator = function(self) {
    if (!inherits(self@db, "SQLiteConnection")) {
      "db must be a `SQliteConnection`"
    }
  }
)
#> <Foo> class
#> @ parent     : <S7_object>
#> @ constructor: function(id, db) {...}
#> @ validator  : function(self) {...}
#> @ properties :
#>  $ id: <character>
#>  $ db: <ANY>

[hadley]

Like this:

library(S7)
library(DBI)

new_class(
  "Foo",
  properties = list(
    id = class_character,
    db = methods::getClass("DBIConnection")
  )
)
#> <Foo> class
#> @ parent     : <S7_object>
#> @ constructor: function(id, db) {...}
#> @ validator  : <NULL>
#> @ properties :
#>  $ id: <character>      
#>  $ db: S4<DBIConnection>

^{Created on 2026-01-12 with reprex v2.1.1}

(Would be slightly easier if DBI exported the constructor/class object)

[JosiahParry]

Thank you! It would be great if this was documented in a smidgen more detail than "compatibility with S4" perhaps in https://rconsortium.github.io/S7/articles/compatibility.html#s4 or elsewhere.

[hadley]

It is mentioned in https://rconsortium.github.io/S7/reference/as_class.html, which https://rconsortium.github.io/S7/reference/new_class.html#arg-properties documents. The vignette could definitely benefit from some examples. Would you be interested in doing a PR?