procproblem.cr

@[Link(ldflags: "#{__DIR__}/test.o")]
lib Testc
  struct TestStruct
    testFunction : (Int32) -> Void 
  end

  fun event = "event"(TestStruct) : Void
end



class Test
  getter value : Int32
  getter test_struct
  def initialize
    @value = 32

    @test_struct = Testc::TestStruct.new
    @test_struct.testFunction = ->test_method(Int32)

  end

  def test_method(to_add : Int32)
    puts @value + to_add
  end

end

test = Test.new()

Testc.event(test.test_struct)

test.c

typedef void (* testFunction) (int *);

typedef struct TestStruct
{
  testFunction   func; 
} TestStruct;

void event( TestStruct  *handler)
{
  handler->func(3);
};