Refactor QuantumVariable methods and data structures

documentation/source/general/changelog/changelog-dev.rst

@@ -166,6 +166,13 @@ Improvements
   ``qm.inpl_mult(X, inverse)``
   (`PR #918 <https://github.com/eclipse-qrisp/Qrisp/pull/918>`_).
 
+- Refactored the remaining methods of :ref:`QuantumVariable <QuantumVariable>`, adding type
+  hints and removing the process-wide registry of live variables (``QuantumVariable.live_qvs``),
+  along with ``QuantumVariable.__del__``. The ``auto_uncompute`` decorator now recognizes the
+  variables a function created by their creation time, and generated fallback names come from a
+  counter alone. Name collisions are still resolved per QuantumSession and when sessions are merged
+  (`PR #989 <https://github.com/eclipse-qrisp/Qrisp/pull/989>`_).
+
 - Fewer qubits for :func:`reflection <qrisp.reflection>`:
   :func:`reflection <qrisp.reflection>` no longer bundles its operations into a
   single gate. The bundling kept every ancilla of the ``state_function`` allocated
@@ -176,6 +183,12 @@ Improvements
   operations instead of a single ``reflection`` gate. Jasp mode is unaffected
   (`PR #947 <https://github.com/eclipse-qrisp/Qrisp/pull/947>`_).
 
+- Refactored some methods of :ref:`QuantumVariable <QuantumVariable>`, adding type
+  hints and simplifying the bookkeeping of live variables. ``QuantumVariable.live_qvs`` no longer
+  has to be swept for dead weak references on every deletion, and ``QuantumVariable.__del__`` has
+  been removed
+  (`PR #989 <https://github.com/eclipse-qrisp/Qrisp/pull/989>`_).
+
 Other New Features
 ------------------
 
@@ -735,11 +748,23 @@ API Changes
   ``QuantumVariable.creation_counter`` instead
   (`PR #882 <https://github.com/eclipse-qrisp/Qrisp/pull/882>`_).
 
+* ``QuantumVariable.live_qvs`` has been removed, and ``QuantumVariable.name_tracker`` is
+  now a ``collections.Counter``. Code that looked up QuantumVariables through ``live_qvs``
+  must keep its own references, or use the ``qv_list`` of the relevant QuantumSession
+  (`PR #989 <https://github.com/eclipse-qrisp/Qrisp/pull/989>`_).
+
 .. Add API changes above this line
 
 Development
 -----------
 
+* Removed the ``None`` check from ``QuantumVariable.__setitem__``. It was written as
+  ``isinstance(type(value), type(None))``, which is never true, so the early return for
+  ``qv[:] = None`` was never executed. It was removed deliberately instead of fixed, because
+  ``None`` can be a valid label, e.g. for ``QuantumVariable.custom([None, ...])``, so
+  ``qv[:] = None`` keeps being passed on to the encoder
+  (`PR #989 <https://github.com/eclipse-qrisp/Qrisp/pull/989>`_).
+
 * Added ``jaspr_to_static_register_jaspr``, which rewrites a Jaspr so that all
   qubits come from a single register of fixed size allocated at program start.
   The CUDA-Q backend in `qrisp-cudaq <https://github.com/eclipse-qrisp/qrisp-cudaq>`_

src/qrisp/core/compilation.py

@@ -59,7 +59,7 @@ def qompiler(
     compile_mcm=False,
     gate_speed=None,
     use_dirty_anc_for_mcx_recomp=True,
-):
+) -> QuantumCircuit:
     if len(qs.data) == 0:
         return QuantumCircuit(0)
 

src/qrisp/core/quantum_session.py

@@ -331,7 +331,6 @@ def register_qv(self, qv: QuantumVariable, size: int | None = None):
         # Register in the list of active quantum variable
         self.qv_list.append(qv)
 
-        QuantumVariable.live_qvs.append(weakref.ref(qv))
         qv.creation_time = QuantumVariable.creation_counter
         QuantumVariable.creation_counter += 1