Introduction to quantities

Quantities are represented by instances of the Quantify::Quantity class. There are a number of ways to initialize quantity objects, each of which require a numerical value and a unit. The unit can be specified using string or symbol representations of any of the unit descriptors described here (name, symbol, label) or with a unit object:

Use the Quantity constructor:

Quantity.new(50, "kilometre")                        #=> <Quantify::Quantity>
Quantity.new(12, "parsecs")                          #=> <Quantify::Quantity>
Quantity.new(28.5, :MJ)                              #=> <Quantify::Quantity>

unit = Unit.ton_uk                                   #=> <Quantify::Unit::NonSI>
Quantity.new(1000, unit)                             #=> <Quantify::Quantity>

Or the shorthand:

50.kilometre                                         #=> <Quantify::Quantity>
12.parsecs                                           #=> <Quantify::Quantity>
28.5.MJ                                              #=> <Quantify::Quantity>
1000.ton_uk                                          #=> <Quantify::Quantity>

Alternatively, quantities can be parsed from strings based on a numerical values and valid unit descriptors. In these cases, an array is returned containing quantity objects representing each recognised quantity:

Quantity.parse("50 kilometres")                      #=> Array of quantity objects
"0.18 volts".to_q                                    #=> Array of quantity objects
"The quantity measured 0.18 volts per second".to_q   #=> Array of quantity objects

These objects can be interrogated:

my_quantity = Quantity.new(50, "kilometres")
my_quantity.value                                    #=> 50
my_quantity.unit                                     #=> <Quantify::Unit::SI>
my_quantity.unit.name                                #=> "kilometre"
my_quantity.unit.symbol                              #=> "kg"
my_quantity.to_s                                     #=> "50 kg"
my_quantity.to_s(:name)                              #=> "50 kilograms"
my_quantity.represents                               #=> "mass"