def_k_block_variables_spec.rb

# Yet another version with suggestions from workmad3 :-)
# This time, pass in the keyword args into the block.
# This means duplicating the definition of valid params, but
# also means you get normal local variables in the method body.

module DefK
  # NOTE: params is for syntactic sugar, and has no bearing on the
  # number of arguments you can call
  def def_k(method_name, *params, kparams, &method_body)
    define_method method_name do |*args|
      kargs =
        if args.last.is_a?(Hash)
          kparams.merge(args.delete_at(-1))
        else
          kparams
        end
      
      args.concat(kargs.values)
      
      method_body.call(*args)
    end
  end
end

class Class
  include DefK
end

class Duck
  def_k :quack, name: "Donald" do |name|
    "QUACK #{name}"
  end
end

class Book
  class << self
    def_k :find, :selector, conditions: "", joins: [ ] do |selector, conditions, joins|
      sql = ["SELECT * FROM books"]
      joins.each do |join_table|
        sql << "LEFT OUTER JOIN #{join_table} ON"
        sql << "books.#{join_table.to_s.chop}_id"
        sql << "= #{join_table}.id"
      end
      sql << "WHERE #{conditions}" unless conditions.empty?
      sql << "LIMIT 1" if selector == :first
      sql.join(" ") + ";"
    end    
  end
end

describe Duck do
  let(:duck) { Duck.new }
  
  describe "#quack" do
    it "quacks like Donald" do
      duck.quack.should eq "QUACK Donald"
    end
    
    it "quacks like Daffy" do
      duck.quack(name: "Daffy").should eq "QUACK Daffy"
    end
  end
end

describe Book do
  describe "#find" do    
    it "supports :all" do
      Book.find(:all).should eq "SELECT * FROM books;"
    end
    
    it "supports :first" do
      Book.find(:first).should eq "SELECT * FROM books LIMIT 1;"
    end
    
    it "supports conditions" do
      Book.find(:all, conditions: "name = 'Animal Farm'").should eq "SELECT * FROM books WHERE name = 'Animal Farm';"
    end
    
    it "supports joins" do
      Book.find(:all, joins: %w[ authors publishers ]).should eq(
        "SELECT * FROM books " +
        "LEFT OUTER JOIN authors ON books.author_id = authors.id " +
        "LEFT OUTER JOIN publishers ON books.publisher_id = publishers.id;"
      )
    end
  end
end

def_k_spec.rb

# This version with workmad3's OpenStruct suggestion

require 'ostruct'

module DefK
  # NOTE: params is for syntactic sugar, and has no bearing on the
  # number of arguments you can call
  def def_k(method_name, *params, kparams, &method_body)
    define_method method_name do |*args|
      if args.last.is_a?(Hash)
        args[-1] = kparams.merge(args.last)
      else
        args << kparams
      end
      
      args[-1] = OpenStruct.new(args[-1])
      
      method_body.call(*args)
    end
  end
end

class Class
  include DefK
end

class Duck
  def_k :quack, name: "Donald" do |kargs|
    "QUACK #{kargs.name}"
  end
end

class Book
  class << self
    def_k :find, :selector, conditions: "", joins: [ ] do |selector, kargs|
      sql = ["SELECT * FROM books"]
      kargs.joins.each do |join_table|
        sql << "LEFT OUTER JOIN #{join_table} ON"
        sql << "books.#{join_table.to_s.chop}_id"
        sql << "= #{join_table}.id"
      end
      sql << "WHERE #{kargs.conditions}" unless kargs.conditions.empty?
      sql << "LIMIT 1" if selector == :first
      sql.join(" ") + ";"
    end    
  end
end

describe Duck do
  let(:duck) { Duck.new }
  
  describe "#quack" do
    it "quacks like Donald" do
      duck.quack.should eq "QUACK Donald"
    end
    
    it "quacks like Daffy" do
      duck.quack(name: "Daffy").should eq "QUACK Daffy"
    end
  end
end

describe Book do
  describe "#find" do    
    it "supports :all" do
      Book.find(:all).should eq "SELECT * FROM books;"
    end
    
    it "supports :first" do
      Book.find(:first).should eq "SELECT * FROM books LIMIT 1;"
    end
    
    it "supports conditions" do
      Book.find(:all, conditions: "name = 'Animal Farm'").should eq "SELECT * FROM books WHERE name = 'Animal Farm';"
    end
    
    it "supports joins" do
      Book.find(:all, joins: %w[ authors publishers ]).should eq(
        "SELECT * FROM books " +
        "LEFT OUTER JOIN authors ON books.author_id = authors.id " +
        "LEFT OUTER JOIN publishers ON books.publisher_id = publishers.id;"
      )
    end
  end
end

Why use args.delete_at(-1) when you can use args.pop?

That's the first thing I though of after hours of staring at args[-1]. It's only a code spike, there are loads of defects in the snippets above. I just wanted to see if the concept had any legs (it does, but it's limping at the moment...).