Poor use of a SolverFactory? about pyomo HOT 2 CLOSED

It is less than ideal (as a solver instance is created upon import), but there is actually very little overhead in creating the interface. Ideally, I have wanted to do an overhaul of ConfigDict's implementation of default to defer the processing of the `default value until the first time the value is requested. That would allow something like:

CONFIG.declare(
    'solver',
    ConfigValue(
        domain=SolverFactory,
        default='gurobi',
        description="A solver to use to solve the continuous subproblems for "
        "calculating the M values",
    ),
)

...and the actual solver object would not be created until the first time the value was accessed.

The advantage of holding the solver instance as part of the transformation configuration is that a user can both set and configure the solver before calling the transformation and those options will persist through all the solves in the transformation.

from pyomo.

I think John's suggestion is what we need in the long run here. Just opened it as a separate issue in #3244

from pyomo.