What I didn’t know about Ruby Numbers

I have been coding with Ruby on rails & React.js for two years now as a professional developer, but I had this feeling that while learning Ruby and Rails, there were tons of little notions that I didn’t really understood. I use to write things in order to learn them so here is a series of short articles about what I didn’t know.

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The Numeric Class

In Ruby, what we call “numbers” are all objects from the Numeric class as we can see on the following diagram :

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Fixnum and Bignum

Fixnum are representing small integers and Bignum are representing big integers. As the doc says : “Holds Integer values that can be represented in a native machine word (minus 1 bit).”

Since ruby 2.4, Fixnum and Bignum are unified under the Integer class, so depending on your ruby version, you will get a different behavior.

Use underscores to improve your readability

You can use underscores to get more readable numbers when they reach one thousand.

Divmod vs Modulo operators

As the doc specifies, Divmod is a method that returns an array containing the quotient and modulus obtained by dividing num by numeric., in other words :

Using the modulo operator (%) with positive values is pretty easy to understand as it gives you the rest of a division :

but using it with negative values can be really complicated. I am not going to explain it deeper here and I prefer to give you some resources that will do it far better than me :

Why is the behavior of the modulo operator (%) different between C and Ruby for negative integers?

Exploring the difference between modulus and remainder in Ruby’s Numeric class

Floats are not exact …

Every developer knows that float are decimal numbers but I didn’t know that floats were inexact real numbers.

This is due to the limited number of bytes that can store a Float, so sometimes a Float is not exactly equals to what you think… And here comes the BigDecimal class.

… but BigDecimals are

BigDecimal provides arbitrary-precision floating point decimal arithmetic. In some precise cases, you will need to use BigDecimal in order to overcome the inexactitude of floats.


The docs says that a rational number can be represented as a pair of integer numbers: a/b (b>0), where a is the numerator and b is the denominator. In other words, rationals are similar to fractions.

You can run all the “+”, “ /”, “-” and “*” operations between Rationals

The last word

I know there are lots of other concepts around the Numeric class but that’s all for this article, feel free to improve my explanation in the comments, I might add more concepts here in the future 👋

Written by

Fullstack developer Rails / React.js https://olivierdumas.dev/

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