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Add builder interface for new switch statement
With the addition of `switch`, we now have a second control-flow construct that - is not a loop, so can have lazily constructed blocks because of contained `break` and `continue` statements - can have multiple blocks that need their resources unifying For the first part, we largely just have to handle things separately to `if`, though the placeholder instructions are much simpler because the placeholder will never need mutating and replacing (c.f. the `else` block). For the second point, we move a bunch of the previously if-specific code into a shared location in order to reuse it. Unlike the `if` case, the `switch` builder uses nested context managers for its cases, because this mirrors a common indentation pattern for switch statements (at least if you're not a Linux kernel developer). We need new special logic to reject statements that are loose in the `switch` context but not a `case` context. We _could_ have just ignored that, but it feels like an easy potential mistake to make, so much better to loudly fail than silently do the wrong thing.
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| # This code is part of Qiskit. | ||
| # | ||
| # (C) Copyright IBM 2022. | ||
| # | ||
| # This code is licensed under the Apache License, Version 2.0. You may | ||
| # obtain a copy of this license in the LICENSE.txt file in the root directory | ||
| # of this source tree or at http://www.apache.org/licenses/LICENSE-2.0. | ||
| # | ||
| # Any modifications or derivative works of this code must retain this | ||
| # copyright notice, and modified files need to carry a notice indicating | ||
| # that they have been altered from the originals. | ||
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| """Private utility functions that are used by the builder interfaces.""" | ||
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| from typing import Iterable, Tuple, Set | ||
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| from qiskit.circuit.exceptions import CircuitError | ||
| from qiskit.circuit.quantumcircuit import QuantumCircuit | ||
| from qiskit.circuit.register import Register | ||
| from qiskit.circuit.classicalregister import ClassicalRegister | ||
| from qiskit.circuit.quantumregister import QuantumRegister | ||
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| def partition_registers( | ||
| registers: Iterable[Register], | ||
| ) -> Tuple[Set[QuantumRegister], Set[ClassicalRegister]]: | ||
| """Partition a sequence of registers into its quantum and classical registers.""" | ||
| qregs = set() | ||
| cregs = set() | ||
| for register in registers: | ||
| if isinstance(register, QuantumRegister): | ||
| qregs.add(register) | ||
| elif isinstance(register, ClassicalRegister): | ||
| cregs.add(register) | ||
| else: | ||
| # Purely defensive against Terra expansion. | ||
| raise CircuitError(f"Unknown register: {register}.") | ||
| return qregs, cregs | ||
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| def unify_circuit_resources(circuits: Iterable[QuantumCircuit]) -> Iterable[QuantumCircuit]: | ||
| """ | ||
| Ensure that all the given ``circuits`` have all the same qubits, clbits and registers, and | ||
| that they are defined in the same order. The order is important for binding when the bodies are | ||
| used in the 3-tuple :obj:`.Instruction` context. | ||
| This function will preferentially try to mutate its inputs if they share an ordering, but if | ||
| not, it will rebuild two new circuits. This is to avoid coupling too tightly to the inner | ||
| class; there is no real support for deleting or re-ordering bits within a :obj:`.QuantumCircuit` | ||
| context, and we don't want to rely on the *current* behaviour of the private APIs, since they | ||
| are very liable to change. No matter the method used, circuits with unified bits and registers | ||
| are returned. | ||
| """ | ||
| circuits = tuple(circuits) | ||
| if len(circuits) < 2: | ||
| return circuits | ||
| qubits = [] | ||
| clbits = [] | ||
| for circuit in circuits: | ||
| if circuit.qubits[: len(qubits)] != qubits: | ||
| return _unify_circuit_resources_rebuild(circuits) | ||
| if circuit.clbits[: len(qubits)] != clbits: | ||
| return _unify_circuit_resources_rebuild(circuits) | ||
| if circuit.num_qubits > len(qubits): | ||
| qubits = list(circuit.qubits) | ||
| if circuit.num_clbits > len(clbits): | ||
| clbits = list(circuit.clbits) | ||
| for circuit in circuits: | ||
| circuit.add_bits(qubits[circuit.num_qubits :]) | ||
| circuit.add_bits(clbits[circuit.num_clbits :]) | ||
| return _unify_circuit_registers(circuits) | ||
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| def _unify_circuit_resources_rebuild( # pylint: disable=invalid-name # (it's too long?!) | ||
| circuits: Tuple[QuantumCircuit, ...] | ||
| ) -> Tuple[QuantumCircuit, QuantumCircuit]: | ||
| """ | ||
| Ensure that all the given circuits have all the same qubits and clbits, and that they | ||
| are defined in the same order. The order is important for binding when the bodies are used in | ||
| the 3-tuple :obj:`.Instruction` context. | ||
| This function will always rebuild the objects into new :class:`.QuantumCircuit` instances. | ||
| """ | ||
| qubits, clbits = set(), set() | ||
| for circuit in circuits: | ||
| qubits.update(circuit.qubits) | ||
| clbits.update(circuit.clbits) | ||
| qubits, clbits = list(qubits), list(clbits) | ||
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| # We use the inner `_append` method because everything is already resolved in the builders. | ||
| out_circuits = [] | ||
| for circuit in circuits: | ||
| out = QuantumCircuit(qubits, clbits, *circuit.qregs, *circuit.cregs) | ||
| for instruction in circuit.data: | ||
| out._append(instruction) | ||
| out_circuits.append(out) | ||
| return _unify_circuit_registers(out_circuits) | ||
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| def _unify_circuit_registers(circuits: Iterable[QuantumCircuit]) -> Iterable[QuantumCircuit]: | ||
| """ | ||
| Ensure that ``true_body`` and ``false_body`` have the same registers defined within them. These | ||
| do not need to be in the same order between circuits. The two input circuits are returned, | ||
| mutated to have the same registers. | ||
| """ | ||
| circuits = tuple(circuits) | ||
| total_registers = set() | ||
| for circuit in circuits: | ||
| total_registers.update(circuit.qregs) | ||
| total_registers.update(circuit.cregs) | ||
| for circuit in circuits: | ||
| for register in total_registers - set(circuit.qregs) - set(circuit.cregs): | ||
| circuit.add_register(register) | ||
| return circuits |
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