Scalar

What is scalar? It is a thin, performant library for measurement conversions.

Table of Contents

1. Installation
2. Usage
3. Developmant

Alternatives

• Measured
• RubyMeasurement
• Ruby Units

Why Scalar?

• Because it is crazy fast:

Benchmark.ips do |r|
  r.report("scalar") { Scalar::Weight.pounds(1) == Scalar::Weight.grams(1) }
  r.report("measured") { Measured::Weight.new(1, :lb) == Measured::Weight.new(1, :g) }
  r.report("r-measurement") { Measurement.parse("1 lb") == Measurement.parse("1 g") }
  r.report("ruby-unit") { Unit.new("1 lb") == Unit.new("1 g") }
end

Calculating -------------------------------------
              scalar    459.099k (± 1.1%) i/s -      2.299M in   5.007574s
            measured     15.573k (±17.0%) i/s -     75.900k in   5.035022s
       r-measurement     21.154k (± 1.8%) i/s -    105.850k in   5.005499s
           ruby-unit      2.630k (± 1.5%) i/s -     13.150k in   5.002066s

• Because it uses a nice method based interface. Scalar::Weight.grams(5).kilograms.scalar == 0.005

Why not Scalar?

• Because you are parsing weights from string input.
• Because you need the accuracy of BigDecimal.

Installation

Add this line to your application's Gemfile:

gem 'scalar'

And then execute:

$ bundle

Or install it yourself as:

$ gem install scalar

Usage

Current measurement types:

Scalar::Weight require 'scalar/weight'

• grams, kilograms, pounds, ounces

Scalar::Length require 'scalar/length'

• millimeters, meters, kilometers, inches, feet, yards, miles

Creating a new measurement object

Scalar::Weight.grams(5) #=> <Scalar::Weight @scalar=5 @unit=:grams>

Converting a measurement to a different unit

m = Scalar::Weight.grams(5)
m.kilograms
#=> <Scalar::Weight @scalar=0.005 @unit=:kilograms>
m.pounds
#=> <Scalar::Weight @scalar=0.02 @unit=:pounds>

Comparing two measurements

Scalar::Weight.grams(5) == Scalar::Weight.kilograms(0.005)
Scalar::Weight.pounds(1) > Scalar::Weight.ounces(1)

Making a new unit type for an existing measurement type

Find base unit:

Scalar::Weight::CONVERSIONS.base_unit

Find the conversion ratio online between the new unit and the base unit and add it with the following:

Scalar::Weight::CONVERSIONS.add name: :metric_tons, base_units_per: 1_000_000
Scalar::Weight::CONVERSIONS.add name: :stone, base_units_per: 6350.29

Development

After checking out the repo, run bin/setup to install dependencies. Then, run rake spec to run the tests. You can also run bin/console for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run bundle exec rake install. To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and tags, and push the .gem file to rubygems.org.

Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/CasperSleep/scalar. This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the Contributor Covenant code of conduct.

License

The gem is available as open source under the terms of the MIT License.