On Mon, 1 Jun 2015 12:56:53 +0000, Shriver, Daniel wrote:
Personally, I'd think having an exception is "better" in this case.
1) the computation is fundamentally invalid, an exception conveys
this well (the same thing is used with other invalid computations
like
division by zero)
When points are gradually removed from a set, the hull of the set
gradually shrinks until it becomes a line. IIUC that line would be
equivalent to an empty region (in 2D space).
Hence, I think that returning an empty region is more logical than
raising an exception.
2) an empty region could be a valid result of some valid operation
(unless you are suggesting creating some "invalid region" that just
conveys the same info- that an exception occurred) this effectively
masks the fact that an invalid operation occurred
I don't propose such an "invalid region".
An "empty region" is a valid region.
A programmer can and should catch exceptions from invalid
computations. They should be able to decide if they want to "ignore"
the problem (such as create something like an empty region) and
continue on, or if they want to follow some other path (halting work,
logging a problem,...). If you return some valid "empty region" you
would mask the exception (or if it is only for invalid computations
you'd be simply recreating it as something other than an exception).
Cf. above. I see it the other way around (any set operation is
meaningful even when applied to an empty set), there is no need
to consider it invalid: if the *caller* does not expect an "empty"
result, he should check and act (i.e. raise an exception).
In my use-case, the shape shrinks, then disappears, than reappears
and grows again, in a "continuous" way; nothing "exceptional" occurs.
If I want apply some geometrical operation to the region that encloses
the shape why should the code handle differently empty and non-empty
regions?
Gilles
-----Original Message-----
From: Gilles [mailto:gil...@harfang.homelinux.org]
Sent: Monday, June 01, 2015 8:38 AM
To: user@commons.apache.org
Subject: [Math] Allow empty "ConvexHull2D"
Hi.
I have a question regarding
public Region<Euclidean2D> createRegion() throws
InsufficientDataException
in ConvexHull2D.
It throws the exception when the number of points is < 3.
One can imagine that rather than aborting it could return an "empty
Region"
(which would seamlessly work with further operations on the Region).
What do you think?
Context: in the course of a program, a "valid" region can undergo
successive
transformation until it is indeed impossible to compute the hull; it
seems
that it would be interesting to not treat that as a hard-failure
(warranting
an exception).
Regards,
Gilles
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