fn parse_externalptr_attrs(input: &DeriveInput) -> Result<ClassSystem>Expand description
Parse #[externalptr(...)] attributes to extract class system.
Supported forms:
#[externalptr(env)]- Environment style (default)#[externalptr(r6)]- R6 class#[externalptr(s3)]- S3 class#[externalptr(s4)]- S4 class#[externalptr(s7)]- S7 class