Struct Embedding in R Programming Language

R supports creating custom data structures using lists and environments, which can be used to simulate struct-like behavior. We’ll use this approach to demonstrate a similar concept to struct embedding.

# Create a base "struct"
base <- function(num) {
  self <- list(num = num)
  
  self$describe <- function() {
    sprintf("base with num=%d", self$num)
  }
  
  class(self) <- "base"
  return(self)
}

# Create a container "struct" that embeds base
container <- function(num, str) {
  self <- list(
    base = base(num),
    str = str
  )
  
  # Add methods from base to container
  self$describe <- self$base$describe
  
  class(self) <- c("container", "base")
  return(self)
}

# Main function to demonstrate usage
main <- function() {
  # Create a container instance
  co <- container(1, "some name")
  
  # Access fields directly
  cat(sprintf("co={num: %d, str: %s}\n", co$base$num, co$str))
  
  # Access through the full path
  cat("also num:", co$base$num, "\n")
  
  # Call the describe method
  cat("describe:", co$describe(), "\n")
  
  # Demonstrate interface-like behavior
  describer <- function(obj) {
    UseMethod("describer")
  }
  
  describer.container <- function(obj) {
    obj$describe()
  }
  
  cat("describer:", describer(co), "\n")
}

# Run the main function
main()

In this R code:

1. We define base and container as functions that return lists with attached methods, simulating struct-like behavior.

2. The container function includes a base instance, similar to embedding in the original example.

3. We use the $ operator to access fields and methods, which is similar to the dot notation in many other languages.

4. To simulate interface-like behavior, we use R’s S3 method dispatch system with UseMethod and method definitions for specific classes.

5. The main function demonstrates creating and using these struct-like objects.

When you run this script, you should see output similar to:

co={num: 1, str: some name}
also num: 1
describe: base with num=1
describer: base with num=1

This R code demonstrates concepts similar to struct embedding, showing how to create composite data structures and share behavior between them. While R doesn’t have built-in support for structs or interfaces, we can use its flexible list and environment systems to achieve similar functionality.