Re: [boost] [geometry] area, length, centroid, behavior

Subject: Re: [boost] [geometry] area, length, centroid, behavior
From: Brandon Kohn (blkohn_at_[hidden])
Date: 2009-02-24 17:02:13

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From: "Matt Calabrese" <rivorus_at_[hidden]>
Sent: Tuesday, February 24, 2009 3:43 PM
To: <boost_at_[hidden]>
Subject: Re: [boost] [geometry] area, length, centroid, behavior

> I question both how common such a logical error would be and why the 
> library
> should be responsible for trying to prevent it.
> While I would agree that all
> attempts should be made to make the library (or rather any library)
> intuitive and difficult to misuse, I don't believe preventing a 
> hypothetical
> mistake by making a function have more strict requirements than necessary 
> is
> a good design decision.

I think in this case it's not a matter of making the function more 
restrictive. The function to calculate area must be specialized for each 
type (or categorical concept) in some way. To create an area function that 
explicitly specializes the behavior for point or line types, one would have 
to create an additional function which does so explicitly. I.e. the 
developer has to add this functionality rather than curtail existing 
functions.

> If in practice a lot of people were accidentally
> passing points to the area function, then maybe this would be more of a
> concern, but I really don't see that as being a problem here. I'd rather
> have the function work in the way that makes sense.

I suppose this is just where I differ from everyone. A point is a 0-simplex. 
It has no units (dimensionless) in content space. A line segment is a 
1-simplex. It has units of length in content space. The 2-simplex (triangle) 
has units of area. A 3-simplex has units of volume and so forth with 
increasing dimension. It doesn't make sense IMO to query the area of a point 
any more than it does to query the length or volume of a point. I cannot see 
a viable use-case for wanting it, and based on that I don't see why the 
developer would want to add additional code to support it.

Brandon