Should model.calibration[:states] return a SVector ?

[albop]

Currently the model.calibration object returns a Vector when indexed with a (many) Symbol (s).
At making it return an SVector would sound like a no brainer, but it raises many complications:

• currently all the user-facing facing APIs take/return regular vectors. For instance in commonsimulate(model,dr,s0), s0 is a vector. Since the most natural way to get this s0 is to do s0 = model.calibration[:states], we would need to accept an SVector instead in addition to a Vector.
• these user-facing functions should definitely accept both kind of inputs. We could just use AbstractArray, but we also want type inference to work on size, so there might be a trade-off there. Essentially we need to find the right way to do the casting here and use it everywhere. I'll open a separate issue for that.
• if you want to start off-equilibrium, you currently do s0 = model.calibration[:states] and for instance s0[1]*=1.01. This wouldn't work with a static vector. We could consider the mutable version MVector but I truly doubt it is worth the trouble.
  (maybe s0[1]*=1.01 could be replaced by s0 = s0 + e[1] where e would be some kind of magical coordinate vector whose dimension would automatically adjust when added to another vector).

Overall I'm inclined to not change what model.calibration returns, or if we really want, introduce some kind of strange looking model.calibration[Point,:states]. But I'm open to discussion. So much so I'm actually opening one.
@sglyon ?

[sglyon]

I think that we should always strive for simplicity in the public facing api. If having the calibration objects returns SVectors instead of Vectors complicates that, we should probably avoid it.

That isn't to say there isn't a clever workaround like what you mention at the end. If anything comes to mind I'll let you know!