From 4af5a369a146c8872fcda3846a292d147a32f862 Mon Sep 17 00:00:00 2001
From: hlogmans <hlogmans@edb.nl>
Date: Fri, 5 Feb 2016 16:12:26 +0100
Subject: [PATCH] accessing C from Ruby part

---
 ...your-Ruby-environment-and-accessing-it..md | 39 +++++++++++++++++--
 1 file changed, 36 insertions(+), 3 deletions(-)

diff --git a/Building-your-Ruby-environment-and-accessing-it..md b/Building-your-Ruby-environment-and-accessing-it..md
index b8ce69c..6c09801 100644
--- a/Building-your-Ruby-environment-and-accessing-it..md
+++ b/Building-your-Ruby-environment-and-accessing-it..md
@@ -1,12 +1,12 @@
 ## Building your Ruby environment
 
-You can create classes both from C and Ruby together. Define the class in Ruby code just as a regular Ruby class, and then add C-code the manipulate the class definition.
+You can create classes both from C and Ruby together. Define the class in Ruby code just as a regular Ruby class, and then add C-code the manipulate the class definition. Or define everything in C. Your choice.
 
 ### Access Ruby from C
 
 Lets first define some class in Ruby code, and try to access this from C:
 
-Create a file `wiki-example.rb` with the following content:
+Create a file `wiki-example.rb` with the following content. This class is already prepared for the next section (manipulating Ruby classes from C). We now only need the 'get_version' method.
 
 `````
 module WikiExample
@@ -74,4 +74,37 @@ Compile this code with `gcc -std=c99 -Iinclude wiki-example.c  	build/host/lib/l
 
 ### Calling C methods from Ruby
 
-Coming soon...
+The strategy is first to update the existing class. Here we add a C-method to the class, but we can even define the module and class from C.
+
+To add a method to a class, we first need a reference to the class. We can copy the lines from the first example for getting a reference to the class WikiManager, of just insert the next lines just before the `If crashed...` comment line.
+
+`````
+	// add the method to the WikiManager class
+	mrb_define_method(mrb, class, "_we_connected", we_connected, MRB_ARGS_NONE());
+
+        // call the connect method on WikiManager
+	mrb_value res2 = mrb_funcall(mrb, c, "connect", 0);
+`````
+
+Then we add the following method between the `#include` and `int main` lines:
+
+`````
+mrb_value 
+we_connected(mrb_state* mrb, mrb_value self){
+	// we need an int from the args
+	mrb_int i = 0;
+
+        // retrieve one arg of type int (see mruby.h)
+	mrb_get_args(mrb, "i", &i);
+
+        // we always need to return a mrb_value object, and mrb_bool_value converts a C bool to a mrb_value.
+	return mrb_bool_value(i >= 2);
+}
+`````
+
+Compile (see above) and run. You will get the output `result: 2`. Now edit the Ruby file and change the get_version to return 1. Do not compile, just run the executable again, and see the output `result: 1
+Connection failed`.
+
+This will give you unlimited results, as you don't even need to recompile to update your Ruby code. Image writing unit-tests in Ruby calling your C-methods in classes. You will be able to mock classes the Ruby-way.
+
+Passing the arguments is quite straightforward (both ways). But someone might update this page with some code on how to pass a C struct to Ruby and use the result.
\ No newline at end of file