Deane Yang wrote:
Eric Lemings wrote:
This brings up a good question. Say you have two objects:
meters m = 1; feet f = 2;
What is the type (or unit) of the following expression?
m + f;
I apologize for repeating myself, but I want this to fail to compile. I do not want implicit conversion of units. I believe I am not completely alone in this view.
No, you're not :-) I too want this to fail; having the ability to explicitly forbid on a calculation by calculation basis would not help ... forget it once, and you're screwed. I know it has been a while, and apparently not many people were swayed, but we did discuss this issue at length a few months back. Implicit conversions imply choosing a "canonical" basis (or unit categories: length, time, etc...) and system of units internally (SI, CGS). Many of the potential users of this library have neither a need nor an interest in doing calculation in SI (think astrophysics ... meters are not useful!), and many of us don't have a use for the fundamental unit categories of the SI either (length and time are the same thing, darn it!). This also leaves out monetary units and what we have called "unit tags". Those of us who do lots of long running calculations in these non-SI or non-standard unit systems seriously can't afford the accuracy damage that loads of implicit conversions carry along -- I work very hard to structure my numerical expressions to minimize roundoff error, and uncontrollable implicit conversions under the hood would be very bad! Additionally, forcing a canonical internal system makes it prohibitively difficult to use non-standard bases (as I would like to do :-) Which is not to say that implicit conversions aren't useful to some, I just think that it's almost always indicative of a design error in the application. But what do I know :-) Perhaps this calls for types that implicitly convert, and types that don't, so that you never use the dangerous types if you don't want them. Oh, and I also want to be able to define my own bases and units and tags and .... I want it all! -- ------------------------------------------------------------------------------- Kevin Lynch voice: (617) 353-6025 Physics Department Fax: (617) 353-9393 Boston University office: PRB-361 590 Commonwealth Ave. e-mail: krlynch@bu.edu Boston, MA 02215 USA http://budoe.bu.edu/~krlynch -------------------------------------------------------------------------------