Unit Conversions

AppleScript provides a number of classes whose sole purpose is to allow you to perform measurement unit conversions. They are implemented as classes so that you can use the as operator to perform the conversion; that is, the conversion is really a coercion.

Because of this implementation, the way you have to speak in order to perform a conversion ends up looking fairly silly. You can’t say 3 feet; you have to coerce 3 (a number) to the feet class, by saying 3 as feet. Now you coerce to the desired class; suppose this is yards. But now you have a value of the yards class. You can’t do anything with it, so you have to coerce it to a number.

So, for example:

on feetToYards(ft)
        return ft as feet as yards as number
end feetToYards
feetToYards(3) -- 1.0

The implemented units are themselves a mixed lot. Many important units, such as acres and hectares, aren’t implemented at all. Table 14-1 provides a list.

Table 14-1. Conversion unit classes

meters

inches

feet

yards

miles

kilometers

centimeters

square meters

square feet

square yards

square miles

square kilometers

liters

gallons

quarts

cubic meters

cubic centimeters

cubic feet

cubic inches

cubic yards

kilograms

grams

ounces

pounds

degrees Celsius

degrees Fahrenheit

degrees Kelvin

A much better list of conversion units is built into Mac OS X by way of the Unix tool units. Here’s a way to use it:

on convert(val, unit1, unit2) set text item delimiters to " " set conv to do shell script ({"units", ...

Get AppleScript: The Definitive Guide now with O’Reilly online learning.

O’Reilly members experience live online training, plus books, videos, and digital content from 200+ publishers.