ruby 46 lines · 8 steps

Comparable semantic versions in Ruby

A SemanticVersion class parses version strings and orders them correctly, including tricky prerelease precedence.

Explained by highlit

Intermediate comparable parsing operator-overloading value-object semver

1class SemanticVersion
include Comparable
3 
attr_reader :major, :minor, :patch, :prerelease
5 
def self.parse(string)
  core, prerelease = string.strip.delete_prefix("v").split("-", 2)
  segments = core.split(".").map { |part| Integer(part) }
  raise ArgumentError, "invalid version: #{string}" unless segments.size == 3
10 
  new(*segments, prerelease)
end
13 
def initialize(major, minor, patch, prerelease = nil)
  @major = major
  @minor = minor
  @patch = patch
  @prerelease = prerelease
end
20 
def <=>(other)
  core = [major, minor, patch] <=> [other.major, other.minor, other.patch]
  return core unless core.zero?
24 
  compare_prerelease(other)
end
27 
def to_s
  base = "#{major}.#{minor}.#{patch}"
  prerelease ? "#{base}-#{prerelease}" : base
end
32 
private
34 
def compare_prerelease(other)
  return 0 if prerelease.nil? && other.prerelease.nil?
  return 1 if prerelease.nil?
  return -1 if other.prerelease.nil?
39 
  identifiers(prerelease) <=> identifiers(other.prerelease)
end
42 
def identifiers(prerelease)
  prerelease.split(".").map { |id| id.match?(/\A\d+\z/) ? [0, Integer(id)] : [1, id] }
end
46end

01 / 01

STEP 01

Walkthrough

Space play ←→ step click any line

Three takeaways

1Including Comparable and defining `<=>` gives you all six comparison operators for free.
2Parsing and validation belong in a factory method so instances are always well-formed.
3SemVer precedence rules — like a missing prerelease outranking one that's present — need explicit encoding, not naive string comparison.

Related explainers

ruby

class Order
  class InvalidTransition < StandardError; end
 
  TRANSITIONS = {

A state machine for order transitions in Ruby

state-machine data-driven error-handling

Intermediate 8 steps

ruby

class CreateOrderItems < ActiveRecord::Migration[7.1]
  def change
    create_table :order_items do |t|
      t.references :order, null: false, foreign_key: { on_delete: :cascade }

Enforcing order-item integrity in Rails

migrations foreign-keys validations

Intermediate 7 steps

rust

use std::cmp::Ordering;
use std::str::FromStr;
 
#[derive(Debug, Clone, PartialEq, Eq)]

Parsing and ordering semantic versions in Rust

parsing trait-implementation ordering

Intermediate 8 steps

ruby

class Registration < ApplicationRecord
  belongs_to :event
 
  validates :email, presence: true, format: { with: URI::MailTo::EMAIL_REGEXP }

Validating registrations in Rails

validations i18n error-handling

Intermediate 8 steps

ruby

class ApacheLogParser
  LINE_PATTERN = /\A(?<ip>\S+)\s\S+\s\S+\s\[(?<time>[^\]]+)\]\s"(?<method>[A-Z]+)\s(?<path>\S+)\s(?<protocol>[^"]+)"\s(?<status>\d{3})\s(?<bytes>\d+|-)/
 
  TIME_FORMAT = "%d/%b/%Y:%H:%M:%S %z"

Parsing Apache logs with named captures

regex named-captures parsing

Intermediate 6 steps

java

public record FixedWidthField(String name, int start, int end) {
 
    public String extract(String line) {
        int from = Math.min(start, line.length());