Qiskit / qiskit / 6567751841

87%

main: 88%

push

github

Add singleton lookup-key logic (#11040)

* Add singleton lookup-key logic

This adds overridable logic for singleton classes to define a "key"
function, which takes the same arguments as its `__init__` and returns a
lookup key that is used as a comparison for returning singletons.  This
lets the standard singleton gates easily return the singleton instance
even when `label` is explicitly set to the default, such as happens
using the idiomatic `QuantumCircuit` methods like `x`.

This keying logic has a simple logical extension to allow more than one
singleton to exist for a single base class.  This functionality is not
yet used by the Qiskit standard library, but can easily be used to
make both closed- and open-controlled versions of gates singletons, or
to allow specific hard-coded parameters for (e.g.) `RZGate` singletons.

The decision on which gates to extend this to can be done in follow-up
commits later.

* Fix unnecessary statement

* :us:

Co-authored-by: Matthew Treinish <mtreinish@kortar.org>

* Update documentation comments

---------

Co-authored-by: Matthew Treinish <mtreinish@kortar.org>

138 of 138 new or added lines in 14 files covered. (100.0%)

73741 of 84796 relevant lines covered (86.96%)

92235.98 hits per line