---
name: ruby-f9c161868c24
description: Expert Ruby programming assistance covering blocks, metaprogramming, Bundler, gems, and modern Ruby 3.x features. Use when developing Rails web apps, writing CLI utilities, or managing Ruby gems.
---

# Ruby

A dynamic, interpreted language known for its elegant syntax.

## When to Use

- **Rapid Web Application Development (Ruby on Rails)**: Building full-stack web applications, startups, and MVPs with unmatched developer velocity.
- **E-Commerce & Digital Storefronts**: Powering platforms like Shopify, Spree Commerce, and custom checkout flows.
- **Developer Tooling & Automation**: Authoring automated DevOps scripts, Homebrew formulas, and Fastlane mobile deployment pipelines.
- **Background Processing & Queues**: Executing asynchronous jobs using Sidekiq backed by Redis.

## Quick Start

```ruby
puts "Hello, World!"

class Greeter
  def initialize(name)
    @name = name
  end

  def say_hi
    puts "Hi #{@name}!"
  end
end

g = Greeter.new("Alice")
g.say_hi
```

## Core Concepts

### Object-Oriented Everything & Dynamic Metaprogramming

Every value in Ruby is a full-fledged object; classes can be modified dynamically at runtime:

```ruby
class Integer
  def to_usd
    "$#{format('%.2f', self)}"
  end
end

puts 100.to_usd # "$100.00"
```

### Blocks, Procs & Enumerable Power

Passes executable code blocks to methods for clean data manipulation:

```ruby
orders = [
  { id: 1, total: 45.0, status: :completed },
  { id: 2, total: 120.0, status: :pending },
  { id: 3, total: 85.0, status: :completed }
]

completed_revenue = orders
  .select { |o| o[:status] == :completed }
  .sum { |o| o[:total] }

puts "Completed Revenue: $#{completed_revenue}" # 130.0
```

### Modern Concurrency (Fibers & Ractor)

Runs true parallel execution without Global VM Lock (GVL) contention using Ractors (Ruby 3+):

```ruby
# Parallel computation across multiple CPU cores
r = Ractor.new do
  # Completely isolated memory space
  1_000_000.times.reduce(:+)
end

puts "Ractor Result: #{r.take}"
```

## Common Patterns

### Pattern Matching with Value Extraction (Ruby 3+)

**Problem**: Verbose nested `if/elsif` conditionals when handling structured JSON API responses.

**Solution**:
Use Ruby 3 native pattern matching:

```ruby
def handle_response(response)
  case response
  in { status: 200, data: { user: { name:, email: } } }
    puts "User found: #{name} <#{email}>"
  in { status: 404, error: msg }
    warn "Not found: #{msg}"
  in { status: (500..) }
    raise "Server error occurred"
  else
    puts "Unknown response format"
  end
end
```

## Best Practices

**Do**:

- Enable YJIT in Production: Launch Ruby with `--yjit` to enable the native Just-in-Time compiler, boosting performance 20-40%.
- Use RuboCop with Modern Presets: Enforce style consistency and detect security pitfalls with automated RuboCop linting.
- Freeze String Literals: Add `# frozen_string_literal: true` at the top of files to reduce heap string allocations.
- Use `Sorbet` or RBS for Type Checking: Add static typing to mission-critical business modules.

**Don't**:

- Use monkey-patching in application code: Overriding core methods globally creates fragile, untraceable bugs across gems.
- Query the database inside loops (N+1): Use `.includes()` or `.preload()` in ActiveRecord to eager-load associations.
- Rescue `Exception`: Always rescue `StandardError` (`rescue => e`); rescuing `Exception` catches system exit and termination signals.

## Troubleshooting

| Error                                                    | Cause                                               | Solution                                                                      |
| :------------------------------------------------------- | :-------------------------------------------------- | :---------------------------------------------------------------------------- |
| `NoMethodError: undefined method '...' for nil:NilClass` | Calling method on a nil object.                     | Use safe navigation operator `object&.method_name`.                           |
| `LoadError: cannot load such file -- ...`                | Gem not installed or missing in Gemfile.            | Run `bundle install` and execute script via `bundle exec ruby script.rb`.     |
| `NameError: uninitialized constant`                      | Constant/Class not required or module nesting typo. | Check file require paths and ensure file naming matches Zeitwerk conventions. |

## References

- [Ruby-Lang](https://www.ruby-lang.org/en/)
- [Ruby Style Guide](https://rubystyle.guide/)


---
Source attribution: G1Joshi
Original project: https://github.com/G1Joshi/Agent-Skills/blob/6a74cf03a8a86dc7d993ead3091b41123dbd0181/skills/languages/ruby/SKILL.md
License: MIT
License information: https://opensource.org/license/mit
Original upstream instructions; downloaded from Mega AI Hub.

## Upstream license notice

MIT License

Copyright (c) 2026 G1Joshi

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.



# Mega AI Hub resource metadata

Creator / publisher: G1Joshi
Original project: https://github.com/G1Joshi/Agent-Skills/blob/6a74cf03a8a86dc7d993ead3091b41123dbd0181/skills/languages/ruby/SKILL.md
Attribution basis: Source repository record

Fields of work: Development & Engineering
Roles: Backend Developer, DevOps / SRE, Full-Stack Developer
Specialties: Backend, Cross Platform
Tools: Rails
Country applicability: Country not specified
Classification basis: Source catalog labels
Instruction SHA-256: f7da153c3f150bc855de820dff3363983b55f244156d8e62ecea554c99824b2a