Raymond Hettinger wrote:
IMO, user input (or the full numeric strings in a text data file) is sacred and presumably done for a reason -- the explicitly requested digits should not be throw-away without good reason.
I still don't understand what's so special about the input phase that it should be treated sacredly, while happily desecrating the result of any *other* operation. To my mind, if you were really serious about treating precision as sacred, the result of every operation would be the greater of the precisions of the inputs. That's what happens in C or Fortran - you add two floats and you get a float; you add a float and a double and you get a double; etc.
Truncating/rounding a literal at creation time doesn't work well when you are going to be using those values several times, each with a different precision.
This won't be a problem if you recreate the values from strings each time. You're going to have to be careful anyway, e.g. if you calculate some constants, such as degreesToRadians = pi/180, you'll have to make sure that you recalculate them with the desired precision before rerunning the algorithm.
Remember, the design documents for the spec state a general principle: the digits of a decimal value are *not* significands, rather they are exact and all arithmetic on the is exact with the *result* being subject to optional rounding.
I don't see how this is relevant, because digits in a character string are not "digits of a decimal value" according to what we are meaning by "decimal value" (i.e. an instance of Decimal). In other words, this principle only applies *after* we have constructed a Decimal instance. -- Greg Ewing, Computer Science Dept, +--------------------------------------+ University of Canterbury, | A citizen of NewZealandCorp, a | Christchurch, New Zealand | wholly-owned subsidiary of USA Inc. | greg.ewing@canterbury.ac.nz +--------------------------------------+