refactor: stop mutating self.variables() in the one-variable shortcut#22
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Solver.__call__ extracted the sole variable name with set.pop() on the return value of self.variables(). Today that set is a fresh copy per call, so no harm is observable — but any future binding optimization that returns cached state would silently corrupt it. Use unpacking ((only_var,) = variables) so the set is never mutated. Regression test in tests/test_solver_one_var_shortcut_invariants.py asserts variables() is stable across the shortcut path. See ai/improvements_2026-05-09.md item #8. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
This was referenced May 11, 2026
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Problem.
Solver.__call__extracted the sole variable name withset.pop()on the return value ofself.variables(). Today that set is a fresh copy per call (so no harm is observable), but any future binding optimization that caches or returns a reference would have the wrapper silently corrupt internal state.Fix.
src/formula/formula.py:69-70— use unpacking(only_var,) = variablesso the set is never mutated.Test.
tests/test_solver_one_var_shortcut_invariants.pypins the invariant:solver.variables()returns the same set before and after the shortcut path, across repeated calls.Full suite 319/319.