How to make Ruby

This is a program that returns 3 as an example.

First, write the source code in C.

// three.c
#include <ruby.h>

static VALUE int_three(void){
   return INT2NUM(3);
}

void Init_three(void){
   rb_define_singleton_method(rb_cInteger, "three", int_three, 0);
}

Create a script to create a Makefile.

# extcof.rb
require 'mkmf'
create_makfile "three"

Make

$ make

Write a Ruby script to call the created program.

# main.rb
require "./three"
p Integer.three

Run

$ ruby main.rb
3