CSC/ECE 517 Fall 2010/ch3 3i IC
Mixing Static and Dynamic Code
Introduction
Many middleware solutions have been developed to combine static and dynamic languages to take advantage of both types of code. Previous wiki chapters have discussed JRuby, a Java implementation Ruby. These solutions allow programmers the productivity luxuries of newer dynamic languages with the speed, low-level functionality, and pre-existing code base of older static languages. Below, we will give even more examples of mixing several widely used dynamic languages with C, C++, and Java.
Mixing Dynamic Code and C/C++
Ruby
CplusRuby
CplusRuby is a gem that allows programmers to call Ruby code within C++ and vice versa. Assuming an installation of Ruby, the CplusRuby can be installed with the following command [2]:
gem install cplus2ruby
An example is given below. In this sample, C code is embedded in the Ruby code.
require 'cplusruby'
class NeuralEntity < CplusRuby
- property :id
end
class Neuron < NeuralEntity
- property :potential, :float
- property :last_spike_time, :float
- property :pre_synapses, :value
- method_c :stimulate, %(float at, float weight), %{
- // this is C code
- selfc->potential += at*weight;
}
- def initialize
- self.pre_synapses = []
- end
end
# generate C file, compile it and load the .so
CplusRuby.evaluate("inspire.cc", "-O3", "-lstdc++")
if __FILE__ == $0
n = Neuron.new
n.id = "n1"
n.potential = 1.0
n.stimulate(1.0, 2.0)
p n.potential # => 3.0
end
In the example above, we declare a class as a C class, but in Ruby syntax. However, we define the method method_c in C syntax. We then use CplusRuby to evaluate the embedded C code to generate a C code file. CplusRuby then compiles the generated C code, which then becomes available to the Ruby code at the bottom, which creates an instance of our C class Neuron. This allows performance sensitive code to be compiled as C, which is much faster than Ruby. These C methods can also call other C methods with native C performance. [6 ]
Python
Using Boost
Boost allows programmers to seamlessly expose C++ classes and function to Python and vice versa. No special tools are needed (however, a build tool will be referenced later). All that is required are the Boost libraries and a C++ compiler. Boost is designed to allow Python to use C++ code with no internal modification to the C++ code that will be wrapped.
Exposing Functions
Below is a “Hello, World!” example.
C++ function
string greet()
{
- return "Hello, World!";
}
Add to C++ so it can be exposed to Python
#include <boost/python.hpp>
BOOST_PYTHON_MODULE(hello_ext)
{
- using namespace boost::python;
- def("greet", greet);
}
Python code that calls C++
import hello_ext # parameter passed to BOOST_PYTHON_MODULE
print hello.greet()
>> Hello, World!
Exposing Classes
C++ Class Declaration
class Person
{
- private string name;
- void setName(string name)
- {
- this->name = name;
- }
- string getName()
- {
- return name;
- }
};
Boost.Python C++ Wrapper
#include <boost/python.hpp>
using namespace boost::python;
BOOST_PYTHON_MODULE(person)
{
- class_<Person>("person")
- .def("getName", &Person::getName)
- .def("setName", &Person::setName);
}
Python Code
import person
student = person.Person()
student.setName('John')
student.getName()
>> John
Lua
SWIG
Previously we've seen specific examples of middleware libraries that allow us to mix specific languages. SWIG (Simplified Wrapper and Interface Generator) is a tool that allows programmers to mix C and C++ programs and libraries with several dynamic languages, including Tcl, Perl, Python, Ruby, PHP, and Lua.
There are two primary purposes for embedding dynamic language code in C/C++
- Faster customization
- Easier to write test scripts, including unit tests
Mixing Dynamic Code and Java
Perl
Using Inline::Java
Java Code
public class Person
{
- String name;
- public getName()
- {
- return name;
- }
- public setName(String newName)
- {
- this.name = newName;
- }
}
Perl Code
#!/usr/bin/perl
use strict; use warnings;
use Inline Java => <<'EOJ';
public class Person
{
- // The class body is shown in the Java Code above
}
EOJ
my $student = Person->new("John Smith");
print $student->getName(), "\n";
(This section on Java and Perl is mostly referenced from [4].)
In the Perl example above, we omit the details of the Java class, since they are detailed above. The declaration 'EOJ' ("end of Java", in this case) at the beginning of the Java class declaration in the Perl code is a qualifier to dictate where to end the Java code. In this particular example, we include the Java code directly in our Perl file. However, you can also include Java code via a file reference.
References
[1] Steve Vinoski. Ruby Extensions. Internet Computing, IEEE, Vol. 10, Issue 5. 2006. pp. 85-87.
[1] http://en.wikipedia.org/wiki/SWIG
[2] Michael Neumann. Cplus2Ruby - Gluing C++ and Ruby together in an OO manner. http://rubydoc.info/gems/cplus2ruby/1.2.0/frames
[3] Dave Abrahams. Boost.Python. http://www.boost.org/doc/libs/1_44_0/libs/python/doc/index.html
[4] Phil Crow. Bringing Java into Perl. http://www.perl.com/pub/2003/11/07/java.html. 2003.
[5] Patrick LeBoutillier. Inline::Java http://search.cpan.org/~patl/Inline-Java-0.52/Java.pod
[6] Michael Neumann. CplusRuby - Gluing C and Ruby. http://www.ntecs.de/blog/articles/2007/09/21/cplusruby-gluing-c-and-ruby/. 2007.