Label and name gate should be merged and QasmQobjInstruction take name as identifier

[1ucian0]

In PR #2173 we introduced the notion of "label" for gates. I hope I could make a compelling argument in Qiskit/qiskit-aer#207 that "label" should not be used as identifier. In the same spirit, I think "name" should not be used as identifier in Instruction.assemble (the type should be used).

We do also agree that a display-as argument in conviant for #2286 . For this purpose, I think a name/label (just one of them) is useful.

For assemble purposes instruction = QasmQobjInstruction(name=self.qobj_name) and each gate should set a class attribute qobj_name.

class Reset(Instruction):
    """Qubit reset."""

    qobj_name = 'reset'

    def __init__(self, name='reset'):
        """Create new reset instruction."""
        super().__init__(name, 1, 0, [])

[1ucian0]

The plan would be:

• introduce qobj_name introduce qobj_name #2395
• stop depending on name (in the drawer, in the dissambler, etc)
• merge label/name into one (I would prefer name over label)
• use label/name in drawing Display custom gate labels in circuit drawer #2286

[jaygambetta]

I would rather not couple (even with names) the qobj and the circuits.

[1ucian0]

You think QasmQobjInstruction should extract the qboj-name from the type of the gate? Currently, instructions and gates have an assemble method. If we want to remove every qobj/circuit couple, the responsibility of assembling should be on the qobj-side, right?

[1ucian0]

From #2395 (comment), we are moving towards a class attribute name for the gate names as a way to join the type and the name of the gates. I'm removing the discussion label.

[ajavadia]

@taalexander seemed to suggest this approach will not be good for pulse

[taalexander]

The issue for pulse is the way pulse's are represented in the Qobj. Each pulse in a pulse instruction references a unique pulse in the pulse_library by its name. However in the pulse module we do not have a pulse library, we simply have instances of SamplePulse which may be instantiated with a pulse and a name (optional if not provided will automatically be assigned).

As pulse instance creation is a much more common pattern than basis gate creation in circuits it would be a very inconvenient and confusing pattern to have to derive a new class for each new pulse with a different name. In my mind creating a SamplePulse with a given set of samples is more akin to creating an instance of a Gate with a set of arguments (such as the angles for u3).

If we were set on this model we could provide a constructor function that would automatically derive and name a new class for each new set of pulse samples, but this seems clunky.

[jakelishman]

I'm going to close this as stale now - the name/label split has largely been resolved to be a purely visual thing (label is used by the drawers), and even that is somewhat on its way out. The concerns about Qobj I think are long since stale as well.

Please feel free to re-open if there's more to discuss.