Five polymorphic interfaces lack a virtual destructor

[gabrielfrasantos]

Severity: medium
Domain: api
Status: VERIFIED — measured against a210d34 on 2026-08-10
Suggested labels: bug, api, undefined-behaviour

Summary

AGENTS.md requires every interface to declare virtual ~I() = default. Five headers
declare pure-virtual methods without any virtual destructor. Deleting a derived object through a
base pointer is undefined behaviour.

Measurement

$ for f in $(grep -rlE 'virtual[^;]*\)[[:space:]]*(const)?[[:space:]]*=[[:space:]]*0[[:space:]]*;' \
      numerical --include=*.hpp | grep -v test); do \
      grep -qE 'virtual ~|~[A-Za-z_]+\(\)[[:space:]]*=[[:space:]]*default' "$f" || echo "$f"; \
  done

Affected files

• numerical/analysis/FastFourierTransform.hpp
• numerical/controllers/interfaces/PidDriver.hpp
• numerical/solvers/Solver.hpp
• numerical/optimization/Optimizer.hpp
• numerical/estimators/Estimator.hpp

For contrast, ControlAffineModel in
numerical/nonlinear_control/FeedbackLinearization.hpp
does it correctly:

virtual ~ControlAffineModel() = default;

Suggested fix

Add virtual ~I() = default; to each. Never = 0 — the policy is explicit about this.

If any of these types are intended to be used only by value or via static polymorphism, mark the
destructor protected and non-virtual instead, and document that.

Notes

The prior audit reported 14 such interfaces; the count dropped to 5 after the neural-network
extraction removed the rest.