Combine Regions about quantica.jl HOT 5 CLOSED

Sounds like a good idea. It might, however, lead to some surprises if a user then tries to apply the && to a function not wrapped with a Region. Something like

sqreg = RegionPresets.square(10)
ringreg = r -> 5 < norm(r) < 10
h |> unitcell(region = sqreg && ringreg)

EDIT: I hadn't realized that you propose to overload combine, not && (which is actually not possible, it needs to be & in any case). In that case (using combine) there should be no surprise, indeed. But see post #121 (comment)

from quantica.jl.

Note also that we have boolean operators on superlattices. This should already work

sqreg = RegionPresets.square(10)
ringreg = r -> 5 < norm(r) < 10
unitcell(supercell(lat, region = sqreg) & supercell(lat, region = ringreg))

from quantica.jl.

In any case, I think we should do this, but not with combine, but directly with &, | and xor, in analogy to the supercell boolean operators, which gives more possibilities.

from quantica.jl.

Oh, I understand! It sounds perfect to me.
I wasn't aware of the possibility to perform boolean operations with superlattices.
I agree that the desired syntax should make use of &, | and xor.

from quantica.jl.

I added ! to the list in #129. Note that the logic fallbacks in Julia give us Boolean expressions with arbitrary number of arguments for free.

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