Function array_ref 

pub unsafe fn array_ref(
    arg_array: *mut ArrayType,
    arg_nSubscripts: i32,
    arg_indx: *mut i32,
    arg_arraytyplen: i32,
    arg_elmlen: i32,
    arg_elmbyval: bool,
    arg_elmalign: i8,
    arg_isNull: *mut bool,
) -> Datum