Extending Ruby in C - converting arguments to c types

Question

How I can do similar for ruby. I am not able to find a example/documentation for casting a variable to object. For example

Local<Object> obj = args[0]->ToObject();
Local<Array> props = obj->GetPropertyNames();

I am re-writing a node extension in ruby. Any sort of help will be very helpful. Thanks

static Handle<Value> SendEmail(const Arguments& args)
{
    HandleScope scope;

    list<string> values;
    Local<Object> obj = args[0]->ToObject();
    Local<Array> props = obj->GetPropertyNames();

    // Iterate through args[0], adding each element to our list
    for(unsigned int i = 0; i < props->Length(); i++) {
        String::AsciiValue val(obj->Get(i)->ToString());
        values.push_front(string(*val));
    }

    // Display the values in the list for debugging purposes
    for (list<string>::iterator it = values.begin(); it != values.end(); it++) {
        cout << *it << endl;
    }

    return scope.Close(args.This());
}

because ruby is not strongly typed, there is no notion of "typecasting" in ruby - it is what it is... you may want to transform and object, or convert it, but casting is meaningless — Uri Agassi
– Uri Agassi, Commented Dec 2, 2014 at 7:27

CCooper · Accepted Answer · 2015-01-02 23:10:23Z

I'm not entirely sure that I understand your question, as you flagged this question as C and your code example is C++, but either way, if you're attempting to extend ruby you'll need to convert ruby values to C types, and if you plan on using C++ data structures, from C types to C++ objects.

Using the Ruby C Api:

#include "ruby.h"
//Define module my_module (this can be any name but it should be the name of your extension
VALUE MyModule = Qnil;
//Initialization prototype - required by ruby
void Init_MyModule();
//method prototype declarations - all methods must be prefaced by method_
VALUE method_get_some_ruby_value();

//actual method
VALUE get_some_ruby_value(VALUE self, VALUE some_value)
{
    //If your value is a ruby string - the StringValue function from ruby will ensure 
    //that you get a string no matter what, even if the type being passed is not a string.
    VALUE r_string_value = StringValue(some_value);

    //Now we tell the Ruby API to give us the pointer to the ruby string 
    //value and we assign that to a native char * in C. 
    char *c_string_value = RSTRING_PTR(r_string_value);

    //Now do something with the char * - for example, turn it into a C++ string
    std::string str(c_string_value);
    // ...do something useful here...

    return Qnil; // If you want to return something back to ruby, you can return a VALUE.   
}
//Ruby calls this to initialize your module in ruby
VALUE Init_MyModule()
{   
    //This defines your module in ruby
    MyModule = rb_define_module("MyModule");
    //This defines the method - the module it is in, the ruby method name, the actual method ruby will call, and the number of arguments this function is expected to take
    rb_define_method(MyModule, "get_some_ruby_value", get_some_ruby_value, 1);
}

If you want to learn about passing structs back and forth between Ruby/C/C++, you'll need to have a thorough understanding of Ruby and the Ruby C API before you start trying to work with C++ objects.

Here are a few excellent resources to get you started:

http://silverhammermba.github.io/emberb/c/ http://java.ociweb.com/mark/NFJS/RubyCExtensions.pdf

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