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StartCountingQubits operation

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Fully qualified name: Std.Diagnostics.StartCountingQubits

operation StartCountingQubits() : Unit

Summary

Starts counting the number of qubits allocated. Fails if qubits are already being counted.

Description

This operation allows you to count the number of qubits allocated until StopCountingQubits is called. The counter is incremented only when a new unique qubit is allocated, so reusing the same qubit multiple times across separate allocations does not increment the counter.

Remarks

This operation is useful for tracking the number of unique qubits allocated in a given scope. Along with StopCountingQubits, it can be used to verify that a given operation does not allocate more qubits than expected. For example,

StartCountingQubits();
testOperation();
let qubitsAllocated = StopCountingQubits();
Fact(qubitsAllocated <= 4, "Operation should not allocate more than 4 qubits.");