View source for Call D from Ruby using FFI

Adam Ruppe posted this example in the [http://forum.dlang.org/post/fatqnbivseurruxsxsoh@forum.dlang.org Learn Forum]. The goal is to write a function in D and call it from Ruby using the Ruby-FFI extension.

==Shorter Version==

Create the file "i.d" containing

<syntaxhighlight lang="d">
import std.stdio;

extern(C)
void hello()
{
	writeln("hi from D");
}
</syntaxhighlight>

Compile it as a shared library. For example, to compile as a 64-bit shared library on Linux, you can do

<syntaxhighlight lang="bash">
dmd -shared -m64 -fPIC -defaultlib=libphobos2.so i.d
</syntaxhighlight>

Create the file "d.rb" containing

<syntaxhighlight lang="ruby">
 require 'rubygems'
 require 'ffi'
 
 module DInterface
   extend FFI::Library
   ffi_lib './i.so'
   attach_function :rt_init, :rt_init, [], :int
   attach_function :rt_term, :rt_term, [], :int
   attach_function :hello, :hello, [], :void
 end
 
 # call init
 DInterface::rt_init
 
 # our function
 DInterface::hello
 
 # terminate
 DInterface::rt_term
</syntaxhighlight>

Run the Ruby file: 

<syntaxhighlight lang="bash">
ruby ./d.rb
</syntaxhighlight>

You should see

 hi from D

If you have the phobos shared lib installed system wide, that should work. If not, you'll get an error about not being able to find the libphobos2.so.whatever.version. In that case, just point the path:

<syntaxhighlight lang="bash">
LD_LIBRARY_PATH=/path/to/dmd2/linux/lib64 ruby ./d.rb
</syntaxhighlight>

==More Convenient Version==

You might want to make it a bit more automatic for the Ruby user. You can do that by calling <code>rt_init</code> in the include file and doing an <code>at_exit</code> for the term.

Create "i.d":

<syntaxhighlight lang="d">
import std.stdio;
import std.conv;

extern(C)
void hello(const char* name)
{
	// remember, it is a C function, so use C string
	// and convert inside
	writeln("hi from D, ", to!string(name));
}
</syntaxhighlight>

Create "d.rb":

<syntaxhighlight lang="ruby">
 require 'rubygems'
 require 'ffi'
 
 module DInterface
   extend FFI::Library
   ffi_lib './i.so'
   attach_function :rt_init, :rt_init, [], :int
   attach_function :rt_term, :rt_term, [], :int
   # now taking a string
   attach_function :hello, :hello, [:string], :void
 end
 
 # call init right here for the user
 DInterface::rt_init
 
 # terminate automatically
 at_exit do
   DInterface::rt_term
 end
</syntaxhighlight>

Create "user.rb":

<syntaxhighlight lang="ruby">
 require './d'
 
 DInterface::hello 'Ruby user!'
</syntaxhighlight>

Compile and run (Linux 64-bit version):

<syntaxhighlight lang="bash">
dmd -shared -m64 -fPIC -defaultlib=libphobos2.so i.d
LD_LIBRARY_PATH=~/d/dmd2/linux/lib64 ruby ./user.rb
</syntaxhighlight>