Summary
CircuitBuilder maintains a separate private bool $hasMeasurement = false; flag, set to true inside push() whenever a measurement gate is added (line 643). Elsewhere in the same class, gateCount() and depth() independently derive equivalent information by scanning $this->gates and filtering on $gate->isMeasurement() (lines 465-468 and 483-486). The flag and the scan are two ways of tracking the same underlying fact — whether any element of $gates is a measurement gate — kept in sync only by push() remembering to set it.
Where
src/Circuit/CircuitBuilder.php:41 ($hasMeasurement declaration)src/Circuit/CircuitBuilder.php:622 (validate() — the sole read site: if (! $this->hasMeasurement))src/Circuit/CircuitBuilder.php:636-647 (push() — the sole write site, line 643)src/Circuit/CircuitBuilder.php:463-469 (gateCount() — independently filters $gates by isMeasurement())
Refactor proposal
Remove the $hasMeasurement field and its assignment in push(); have validate() instead check directly, e.g. array_any($this->gates, fn (Gate $g): bool => $g->isMeasurement()) (or ! empty(array_filter(...)) for the current PHP baseline), matching the pattern gateCount()/depth() already use. This is O(n) instead of O(1), but $gates arrays here are circuit-sized (tens of gates at most), so the cost is immaterial next to removing a hand-maintained invariant.
Severity: low
Summary
CircuitBuildermaintains a separateprivate bool $hasMeasurement = false;flag, set totrueinsidepush()whenever a measurement gate is added (line 643). Elsewhere in the same class,gateCount()anddepth()independently derive equivalent information by scanning$this->gatesand filtering on$gate->isMeasurement()(lines 465-468 and 483-486). The flag and the scan are two ways of tracking the same underlying fact — whether any element of$gatesis a measurement gate — kept in sync only bypush()remembering to set it.Where
src/Circuit/CircuitBuilder.php:41($hasMeasurementdeclaration)src/Circuit/CircuitBuilder.php:622(validate()— the sole read site:if (! $this->hasMeasurement))src/Circuit/CircuitBuilder.php:636-647(push()— the sole write site, line 643)src/Circuit/CircuitBuilder.php:463-469(gateCount()— independently filters$gatesbyisMeasurement())Refactor proposal
Remove the
$hasMeasurementfield and its assignment inpush(); havevalidate()instead check directly, e.g.array_any($this->gates, fn (Gate $g): bool => $g->isMeasurement())(or! empty(array_filter(...))for the current PHP baseline), matching the patterngateCount()/depth()already use. This is O(n) instead of O(1), but$gatesarrays here are circuit-sized (tens of gates at most), so the cost is immaterial next to removing a hand-maintained invariant.Severity: low