what is the type of PI, cos in Ruby

Question

I want to ask about the type of PI and cos with Ruby. What is the convention to write these types?

Can I write like: Math::sin, Math::PI or Math.sin, Math.PI?

Answer 1

puts Math::PI
#=> 3.141592653589793
include Math
puts PI.class
#=> Float
require "bigdecimal/math"
include BigMath
puts PI(50).class
#=> BigDecimal
puts PI(50)
#=> 0.3141592653589793238462643383279502884197169399375105820974944592309049629352442819E1

Answer 2

PI is a constant that belongs to the Math module. Constants are accessed through the :: operator:

Math::PI

I believe it is called the scope resolution operator. It can also resolve to class methods, so you can definitely write:

Math::sin

The dot operator sends messages to objects, which is a fancy way of saying it calls methods. PI is a constant, so you can't access it that way. Math.PI is equivalent to Math.send :PI, which doesn't work since Math doesn't respond_to? :PI. Of course, you can fix that:

def Math.PI
  Math::PI
end

Math.PI

With method_missing, you can even make it work with any constant:

def Math.method_missing(method, *arguments, &block)
  Math.const_get method, *arguments, &block
end

Math.PI
Math.E

Answer 3

First, there is no Math.PI, it's Math::PI--in this case, use the one that actually works.

[1] pry(main)> Math.PI
NoMethodError: undefined method `PI' for Math:Module
[2] pry(main)> Math::PI
=> 3.141592653589793

sin etc. are functions, and may be accessed either way. I use dot-notation, Math.sin(foo), because it's easier on the eyes (matter of opinion), and similar to how other Rails code is canonically written (like Rails' ActiveRecord findAll, e.g., User.findAll), and how most other languages I use regularly do it.

Edit Oh, I may have misunderstood the question.