This question already has an answer here:
Consider the following discretization of a region object:
region = DiscretizeRegion[Disk, MaxCellMeasure -> ∞] Head[region] InputForm[region]
which returns something like this:
By all appearances, this has created an object
region with Head
MeshRegion and which contains a bunch of points, then a
Polygon object, and other stuff inside.
I am trying to manipulate regions of this kind using standard mess-with-the-code techniques, but they're proving surprisingly ineffective. Consider the following ways to get at the juicy interior:
Replace the head with something else, e.g. via
notMeshRegion @@ region,
which doesn't do anything.
Attack it via
Part, to get at the inner components of the expression,
doesn't work, and it returns a
Attempt to replace the head or internals of the expression with something else,
which leaves it untouched.
What's going on? I might expect this kind of thing to happen with objects with
HoldAll attributes (so their internals are a bit weird and they do some nonstandard handling), but
MeshRegion's only attribute is
Protected, and under
region looks exactly like every other expression. How do I get to those juicy internals?
I thought this would be obvious, since we're all grownups, but just to be clear: I'm not asking about WRI's design reasons for making the language behave like it does, which is obviously a question for WRI instead of this site. I'm asking about what features of the language cause some expressions, which can have intricate an intricate internal structure evident through
FullForm to make that internal structure unavailable via the normal language tools, where they are represented in the documentation, and how I can use the language to tell whether a given expression will behave this way.