pub type TwigLanguageCallFn = unsafe extern "C" fn(user_data: *mut c_void, call: *const TwigLanguageCall, out: *mut *mut u8, out_len: *mut usize) -> c_int;Expand description
A language function: call in, and on success an allocation of the
host’s out through out/out_len, returning 0. On failure it returns
non-zero and may hand out a UTF-8 message the same way. Twig releases
whatever it hands out with the table’s free.