"Introduction"

I'm relatively new to C++. I went through all the basic stuff and managed to build 2-3 simple interpreters for my programming languages.

The first thing that gave and still gives me a headache: Implementing the type system of my language in C++

Think of that: Ruby, Python, PHP and Co. have a lot of built-in types which obviously are implemented in C. So what I first tried was to make it possible to give a value in my language three possible types: Int, String and Nil.

I came up with this:

enum ValueType
{
     Int, String, Nil
};

class Value
{
 public:
  ValueType type;
  int intVal;
  string stringVal;
};

Yeah, wow, I know. It was extremely slow to pass this class around as the string allocator had to be called all the time.

Next time I've tried something similar to this:

enum ValueType
{
     Int, String, Nil
};

extern string stringTable[255];
class Value
{
 public:
  ValueType type;
  int index;
};

I would store all strings in stringTable and write their position to index. If the type of Value was Int, I just stored the integer in index, it wouldn't make sense at all using an int index to access another int, or?

Anyways, the above gave me a headache too. After some time, accessing the string from the table here, referencing it there and copying it over there grew over my head - I lost control. I had to put the interpreter draft down.

Now: Okay, so C and C++ are statically typed.

  • How do the main implementations of the languages mentioned above handle the different types in their programs (fixnums, bignums, nums, strings, arrays, resources,...)?

  • What should I do to get maximum speed with many different available types?

  • How do the solutions compare to my simplified versions above

c++ interpreter typing
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