Qiskit / qiskit / 6090579658

87%

main: 89%

push

github

Enforce type-safety in `NeighborTable` (#10774)

This hides the internal `.neighbors` field in favour of instead
implemented `Index<PhysicalQubit>` on the entire `NeighborTable` struct.
This is done because indexing into `.neighbors` required calling
`PhysicalQubit::index` to retrieve a `usize`, but a similar method also
exists on `VirtualQubit`.  This meant that it was previously a normal
API pattern to do `neighbors.neighbors[qubit.index()]`, and this threw
away the type safety: it would compile without warning whether `qubit`
was physical or virtual.

To support the hiding of the `.neighbors` field, the constructor of the
coupling map is moved to be an associated function on `NeighborTable`,
so the unsafe access only happens within the context of all other unsafe
operations.

16 of 16 new or added lines in 2 files covered. (100.0%)

74439 of 85276 relevant lines covered (87.29%)

90248.83 hits per line