Dynamic Ruby Features และ Metaprogramming แบบมีวินัย

QueryBuilder.new.where(:status, "active").where(:role, "admin")

public_send(operation, a, b)

[:cpu, :memory].each do |name|
  define_method("track_#{name}") do |value|
    "tracking #{name}=#{value}"
  end
end

def where(key, value)
  @query[key] = value
  self
end

# EXAMPLE CODE
# Topic: topic_08_ruby_specific_features
#
# Purpose:
# - This file demonstrates reference implementation for the concept.
# - It should pass tests from the beginning.
# - Read and understand it before solving exercises.

class CalculatorOps
  def add(a, b) = a + b
  def sub(a, b) = a - b

  def apply(operation, a, b)
    public_send(operation, a, b)
  end
end

# STUDENT TASK (BASIC)
# Topic: topic_08_ruby_specific_features
#
# What to do:
# - Implement or improve the class/methods in this file.
# - Read tests in tests/topic_08_ruby_specific_features_spec.rb under the "basic exercise" examples.
# - Make tests pass without breaking the example/advanced sections.
#
# Expected outcome:
# - You can run this topic tests and see all examples green after implementation.

class Metrics
  [:cpu, :memory].each do |name|
    define_method("track_#{name}") do |value|
      "tracking #{name}=#{value}"
    end
  end
end

# STUDENT TASK (ADVANCED)
# Topic: topic_08_ruby_specific_features
#
# Academic purpose:
# - Demonstrate a dynamic Ruby pattern that feels close to domain language rather than mere syntax trickery.
# - Evaluate metaprogramming by readability and usefulness.
#
# Real-world use case:
# - Query builders appear in ORMs, search interfaces, filtering layers, and internal DSLs.
# - Chaining methods such as `where(:status, "active")` can make intent very readable.
# - This is a better teaching example than abstract runtime dispatch because students can imagine using it.
#
# Why Ruby is beautiful here:
# - Returning `self` makes the API feel fluid.
# - The method names become part of a tiny language for expressing intent.
# - The resulting object can stay simple while the call site becomes expressive.
#
# What to do:
# - Complete the challenge behavior requested by the guide.
# - Be able to explain why this is a good DSL-style example and where the pattern should stop.
# - Use tests in tests/topic_08_ruby_specific_features_spec.rb under the "advanced exercise" examples.
#
# Expected outcome:
# - Advanced tests pass and you can discuss both the beauty and the risk of dynamic APIs.

class QueryBuilder
  def initialize
    @query = {}
  end

  def where(key, value)
    @query[key] = value
    self
  end

  def to_h
    @query.dup
  end
end

# ANSWER KEY (BASIC)
# Topic: topic_08_ruby_specific_features
#
# Solution idea:
# - The methods all share the same shape, so `define_method` removes repetition.
# - This is a reasonable use of metaprogramming because the generated API is small and obvious.

class Metrics
  [:cpu, :memory].each do |name|
    define_method("track_#{name}") do |value|
      "tracking #{name}=#{value}"
    end
  end
end

# ANSWER KEY (ADVANCED)
# Topic: topic_08_ruby_specific_features
#
# Solution idea:
# - Build a chainable API by storing filter pairs in an internal hash.
# - Return `self` from `where` so multiple calls can read like a tiny query DSL.
# - Return a duplicated hash so callers do not mutate internal state accidentally.

class QueryBuilder
  def initialize
    @query = {}
  end

  def where(key, value)
    @query[key] = value
    self
  end

  def to_h
    @query.dup
  end
end

# This spec is your learning companion for topic_08_ruby_specific_features.
#
# How to use this file:
# 1) Run tests and observe failures/successes.
# 2) Keep EXAMPLE specs green from the beginning.
# 3) Implement BASIC exercise until BASIC specs pass.
# 4) Implement ADVANCED exercise and pass edge cases.
#
# Expected final result:
# - All examples in this file pass.
# - You understand both the concept and the implementation tradeoffs.

require_relative "../example"
require_relative "../basic_exercise"
require_relative "../adv_exercise"

RSpec.describe "topic_08_ruby_specific_features" do
  describe "EXAMPLE purpose: understand the reference implementation" do
    it "applies dynamic operation via public_send" do
      c = CalculatorOps.new
      expect(c.apply(:add, 2, 3)).to eq(5)
      expect(c.apply(:sub, 7, 4)).to eq(3)
    end
  end

  describe "BASIC EXERCISE purpose: implement the comparable task" do
    it "tracks dynamically defined metrics" do
      m = Metrics.new
      expect(m.track_cpu(70)).to eq("tracking cpu=70")
      expect(m.track_memory(256)).to eq("tracking memory=256")
    end
  end

  describe "ADVANCED EXERCISE purpose: solve challenge and edge cases" do
    it "builds chainable query hashes" do
      q = QueryBuilder.new.where(:status, "active").where(:role, "admin")
      expect(q.to_h).to eq({ status: "active", role: "admin" })
    end
  end
end

#!/usr/bin/env bash
set -euo pipefail

SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
ROOT_DIR="$(cd "${SCRIPT_DIR}/.." && pwd)"

exec "${ROOT_DIR}/run_tests.sh" "$(basename "${SCRIPT_DIR}")"