Calling Ruby Method from Crystal

[mgomes]

Hello,

I'd like to call a method from Crystal in my Ruby code. In the test suite I see that being done with code like this:

def class_call_test
    puts Anyolite.call_rb_method_of_class(self.class, :class_method_in_ruby, ["World", 4], cast_to: String)
end

The problem I am having is that Anyolite.call_rb_method_of_class only takes a class as the first argument. That means that I'd have to know the class name in advance and also have the same class declared in Crystal. Is there another way to do it?

Thanks!

[Hadeweka]

Hi,

as far as I understand this, you want to call a Ruby class method where the name of the class and the name of the method are known, but the Ruby class has no analogue in Crystal (please correct me otherwise)?

It seems that I forgot to actually implement a proper method for this case, so definitely thank you for pointing it out!
I will try to fix this in the next days.

Until then, you can do something like this:

class_name = "TestModule::Test"
method_name = "class_method_in_ruby"
args = ["World", 4]

rb_class = rb.execute_script_line(class_name)
result = Anyolite.call_rb_method_of_object(rb_class, method_name, args, cast_to: String)

You get the Ruby class by just putting its name into a script line, which then returns a RbValue (the internal representation of the Ruby object). Then, you can just call the method name with the RbValue as the object.

This does not only work for classes, but all other objects which are somehow accessable from a global context.

I hope I could help you, otherwise please feel free to ask.

[mgomes]

@Hadeweka That's the exact the use case I am going for. Thanks! I'm implementing a system where some events happen in Crystal and Crystal calls out to user-defined scripts written in MRuby and so the entry point is always known.

This workaround is perfect. Thanks for considering adding native support for it as well!

[Hadeweka]

With the 0.14.0 release, the following code will be possible:

rb_module = Anyolite::RbModule.get_from_ruby_name(rb, "TestModule")

if rb_module
  rb_class = Anyolite::RbClass.get_from_ruby_name(rb, "Test", under: rb_module)

  if rb_class
    method_name = "class_method_in_ruby"
    args = ["World", 4]

    class_obj = rb_class.to_rb_obj

    result = Anyolite.call_rb_method_of_object(class_obj, method_name, args, cast_to: String)
  end
end

This does on the first glance not look like an improvement, but you can actually now obtain classes and modules by their name using Anyolite::RbClass.get_from_ruby_name without calling any script lines. This gives a Anyolite::RbClass object, which in turn can be transformed into a Ruby object by calling to_rb_obj.

The tests are necessary because a class may not exist, in which case rb_class will become nil. In my opinion it is more in the spirit of Crystal to do so and produces safer code.

Overall, the way this can be done currently is still a bit chaotic, but I have this on my list for a future release. That's also the reason why the version number is only 0.14.0 instead of 1.0.0 ;-)

(Edit: Typo)

[mgomes]

Amazing! This will work great.

Thanks so much for the release.