Pass text to C

Choose the text adapter to match C’s signature. as utf8 lends a pointer and byte length without allocating. as c_string makes a terminated copy and reports embedded NULs or allocation failure through CStrError.

Save this interface as c_text.plentyi:

# strlen reads only during the call and does not retain or return its input.
# C signature: size_t strlen(const char *text).
pub extern def byte_length(text: &str as c_string) -> Result[u64, CStrError] = "strlen"

import c_text

def main() -> Result[(), AllocError | IoError | CStrError]:
    text = "é"
    print(c_text.byte_length(&text)?)?
    with_nul = "a\0b"
    match c_text.byte_length(&with_nul):
        case Ok(size):
            print(size)?
        case Err(error):
            print(error)?
    print(text)?
    Ok(())

2
CStrError.EmbeddedNul
é

The C call returns a plain size_t, which is u64 on this target. The generated adapter returns Result[u64, CStrError] because preparing the argument may fail. The temporary buffer is freed after the call; the original text is unchanged. CStrError.Allocation(error) reports a failed buffer allocation. These conversion errors do not replace any error status that the C function itself returns.

An interface for uint64_t checksum(const uint8_t *data, size_t size) would instead declare text: &str as utf8. It receives all bytes, including embedded NULs, and needs no temporary copy. Neither adapter lets C retain or modify the buffer. Use a binding with an explicit ownership contract for those cases.