Python list type representation in C/C++

[yfinkelstein]

Hello,
the type mapping table https://docs.exaloop.io/integrations/cpp/cpp-from-codon/#type-conversions
is missing any info on how to pass array/list from C++ to codon.

For instance, if I have

@export
def run(argv:list[str]) -> None:

how do I invoke run from C++?

Thank you!

[arshajii]

Hi @yfinkelstein -- it's recommended to not pass the list itself across the Codon-C++ boundary, but to instead pass the pointer and length:

def run(argv: Ptr[str], argc: int) -> None:

You can access a list's internal pointer via list.arr.ptr.

To answer your question though, the list representation in C++ would be:

struct str {
  int64_t len;
  char *ptr;
};

struct array {
  int64_t len;
  str *ptr;
};

struct list {
  int64_t len;  // logical list length
  array arr;    // array length is list capacity
};

A List[str] object in Codon would then correspond to a list* in C/C++.