conversion of unit to string

[fkloosterman]

Hi,

Thanks for the nice library. I have been playing with it to convert strings to measurements or units, and so far it works well. When converting back to a string, though, the original representation of the unit is lost. For example, if I define a custom count unit samples, then the string "samples/second" is correctly parsed, but converting the resulting unit back to a string results in Bq. What is the recommended way to preserve the original unit representation?

Separately, I was wondering if the unit Hz should actually be defined as count per second (i.e. counting the number of cycles per second). This would then make it compatible with samples/second (sampling rate) and spikes/second (firing rate of brain cells) that are generally expressed in Hz. Alternatively, I don't define samples and spikes as count units, but then I wonder how I could differentiate after conversion of a string to a measurement between "2" and "2 samples" without parsing the string again myself.

-Fabian

[phlptp]

The original conversion is lost, there is no way to store the original string in a very compact data structure. So generally the to string operations convert to the most compact representation. Still some bugs I am sure, but the general requirement was that the string produced needed to be able be converted back into the same unit.

A Bq is a count/sec usually used in counting radioactivity so technically correct but obviously not what you might be looking for.

so options would include

units::precise_unit samples=generate_custom_count_unit(3);
addUserDefinedUnit("samples",samples);

Then it would never get mistaken for a count. and the string would produce
"samples/s" Though if you really wanted samples/second at that point

addUserDefinedUnit("samples/second", samples/precise::s);

Side Note: still need to generate more documentation on generating custom_units and custom_count_units.

[phlptp]

As for Hz Kind of an interesting discussion I suppose. On the systems I interact with it would be more appropriate to have Hz be defined at 2*pi*rad/s but then the relationship of second==Hz.inv() wouldn't work. Though there are routines in the convert methods that deal with conversions between radians, count, and moles.

As far as counting of specific things I have either used a custom_count_unit or use the commodity field of the precise_unit type to keep track of what it is. Though based on your comment I might want to revisit the use of Bequerel in the case of count/s for string output, maybe I should just take that out of the string output as it seems to be more of niche unit and could be confusing in other fields.

[phlptp]

added documentation
and removed Bq from the unit to string conversion since that is an uncommon unit and often was confusing.