function having methods

While going through the Learning Go - An Idiomatic Approach to Real-World Go Programming book by Jon Bodner, I learned that functions can have methods.

  package main

  import "fmt"

  type Foobar func()

  func (foobar Foobar) Run() {
  	foobar()
  }

  func main() {
  	helloworld := func() {
  		fmt.Println("helloworld")
  	}
  	foobar := Foobar(helloworld)
  	foobar.Run()
  }

This adds to the "first-class functions" principle that Go adheres to.

Not too long after, I was also surprised to discover a similar pattern in a Rust library:

  trait Foobar {
  	  fn run(&self);
  }

  impl<F> Foobar for F
  where
      F: Fn(),
  {
  	  fn run(&self) {
  		    self()
  	  }
  }

  fn main() {
  	  let it = || println!("Hello, world!");
  	  it.run();
  }

It's only a little bit different as we don't need a type conversion; we can invoke the run method differently on the closure!