Class Systems | miniextendr

miniextendr supports five R class systems. Switch between them with a single attribute change.

🔗Quick Comparison

Feature	Env	R6	S3	S4	S7
Attribute	`#[miniextendr]`	`#[miniextendr(r6)]`	`#[miniextendr(s3)]`	`#[miniextendr(s4)]`	`#[miniextendr(s7)]`
Method Call	`obj$method()`	`obj$method()`	`generic(obj)`	`generic(obj)`	`generic(obj)`
Encapsulation	Weak	Strong	None	Moderate	Strong
Dependencies	None	R6 package	None	methods package	S7 package
Active Bindings	No	Yes	No	No	Yes
Inheritance	No	Limited	S3 dispatch	S4 dispatch	S7 dispatch
Best For	Simple APIs	Complex state	Tidyverse compat	Bioconductor	Modern OOP

🔗Choosing a Class System

Simple internal API? Use Env (default) – no dependencies, $ dispatch
Complex stateful objects? Use R6 – active bindings, encapsulation
Tidyverse / generic functions? Use S3 – print.MyClass, format.MyClass
Bioconductor ecosystem? Use S4 – formal classes, multiple dispatch
Modern R OOP? Use S7 – best of S3 + S4, computed properties

🔗Environment Style (Default)

#[derive(miniextendr_api::ExternalPtr)]
pub struct Counter { value: i32 }

#[miniextendr]
impl Counter {
    pub fn new(initial: i32) -> Self {
        Counter { value: initial }
    }

    pub fn value(&self) -> i32 { self.value }

    pub fn increment(&mut self) { self.value += 1; }
}

c <- Counter$new(0L)
c$value()      # 0
c$increment()
c$value()      # 1

🔗R6 Style

#[miniextendr(r6)]
impl Counter {
    pub fn new(initial: i32) -> Self {
        Counter { value: initial }
    }

    pub fn value(&self) -> i32 { self.value }

    // Active binding (property-like access)
    #[miniextendr(r6(active))]
    pub fn current(&self) -> i32 { self.value }
}

c <- Counter$new(0L)
c$value()    # Method call
c$current    # Active binding (no parens)

🔗S3 Style

#[miniextendr(s3)]
impl Counter {
    pub fn new(initial: i32) -> Self {
        Counter { value: initial }
    }

    pub fn value(&self) -> i32 { self.value }
}

c <- new_Counter(0L)
value(c)     # S3 generic dispatch
print(c)     # Uses print.Counter if defined

🔗S4 Style

#[miniextendr(s4)]
impl Counter {
    pub fn new(initial: i32) -> Self {
        Counter { value: initial }
    }

    pub fn value(&self) -> i32 { self.value }
}

🔗S7 Style

#[miniextendr(s7)]
impl Counter {
    pub fn new(initial: i32) -> Self {
        Counter { value: initial }
    }

    pub fn value(&self) -> i32 { self.value }
}

🔗Trait Methods

Trait implementations can be exposed to R as method groups:

trait Describable {
    fn describe(&self) -> String;
}

#[miniextendr]
impl Describable for Counter {
    fn describe(&self) -> String {
        format!("Counter({})", self.value)
    }
}

In R, trait methods are accessible via Type$Trait$method(obj) (standalone) or obj$Trait$method() ($ dispatch).