Qiskit / qiskit / 21713493341

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push

github

Committed by web-flow

Commit Message

Add `CircuitData::from_dag_ref` constructor (#15557)

* Add `CircuitData::from_dag_ref` constructor

This logically replaces the separate `dag_to_circuit` function.  Aside
from requiring less code, because there's no need to define new custom
"transfer" data types or document a long option list, this is more
performant because the circuit can more easily pre-allocate space for
its complete expansion.

It is typically more convenient in Rust to have constructor functions
defined on the object to be constructed, since methods defined by the
struct have private access to its internals.  This makes `from_*`
methods typically rather simpler than separated constructors.

`from_dag_ref` and `from_dag_ref_deepcopy` are split for two reasons:

1. it's clear that we must be attached to a Python interpreter to call
   `from_dag_ref_deepcopy`, and caller must ensure this, without us
   needing to re-check the attachment on each instruction.

2. ideally, `CircuitData::from_dag_ref` could be made infallible.  In
   practice, there are still some problems, because one could introduce
   parameters with clashing names while in the `DAGCircuit` form, which
   would cause the tracking to fail on conversion.

* Remove use of `dag_to_circuit` from `cext`

We already make the assumption within all these passes that there are no
Python operations internally, so we can directly use the converter that
does not attempt to access `deepcopy`.

* Add whitespace between functions

Run Details

78 of 80 new or added lines in 15 files covered. (97.5%)

4 existing lines in 3 files now uncovered.

99970 of 113638 relevant lines covered (87.97%)

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