Parameter cache is preserved after copy_empty_like

[nkanazawa1989]

Environment

• Qiskit version: main
• Python version:
• Operating system:

What is happening?

Parameter appears in empty circuit after copy

How can we reproduce the issue?

p1 = Parameter("P1")
qc = QuantumCircuit(1)
qc.rz(p1, 0)
qc.parameters  # dummy call to fill cache

cpy = qc.copy_empty_like()
cpy.parameters

I see

ParameterView([Parameter(P1)])

which should not exist.

What should happen?

Parameter should be empty

Any suggestions?

Nullify _parameters after copy

[jakelishman]

Thanks for the report Naoki. I think this has actually been in existence for some time, more than just the Rust changes.

[jakelishman]

Yeah, this appears to be in 1.1 and 0.46 - might well have been around for a long time.