factor out some utilities for pointer arrays

lib/src/util.rs

@@ -1,5 +1,34 @@
 use crate::string::TCString;
+use crate::traits::*;
+use std::ptr::NonNull;
 
 pub(crate) fn err_to_tcstring(e: impl std::string::ToString) -> TCString<'static> {
     TCString::from(e.to_string())
 }
+
+/// A version of Vec::into_raw_parts, which is still unstable.  Returns ptr, len, cap.
+pub(crate) fn vec_into_raw_parts<T>(vec: Vec<T>) -> (*mut T, usize, usize) {
+    // emulate Vec::into_raw_parts():
+    // - disable dropping the Vec with ManuallyDrop
+    // - extract ptr, len, and capacity using those methods
+    let mut vec = std::mem::ManuallyDrop::new(vec);
+    return (vec.as_mut_ptr(), vec.len(), vec.capacity());
+}
+
+/// Drop an array of PassByPointer values
+pub(crate) fn drop_pointer_array<T>(mut array: Vec<NonNull<T>>)
+where
+    T: 'static + PassByPointer,
+{
+    // first, drop each of the elements in turn
+    for p in array.drain(..) {
+        // SAFETY:
+        //  - p is not NULL (NonNull)
+        //  - p was generated by Rust (true for all arrays)
+        //  - p was not modified (all arrays are immutable from C)
+        //  - caller will not use this pointer again (promised by caller; p has been drain'd from
+        //    the vector)
+        drop(unsafe { PassByPointer::take_from_arg(p.as_ptr()) });
+    }
+    drop(array);
+}