RubyTapas #033 - #038

033 Classes and Constants

？

Point = Class.new do
  attr_reader :x, :y

034 Struct from Hash

★

Beer = Struct.new(:brewery, :name, :abv, :ibu) do
  def self.from_hash(attributes)
    instance = self.new
    attributes.each do |key, value|
      instance[key] = value
    end
    instance
  end

struct to hash

  def attributes
    result = {}
    members.each do |name|
      result[name] = self[name]
    end
    result
  end

035 Callable

？

five different kinds of object which respond to the #call message

1. A lambda
2. A method object
3. A symbol converted to a Proc
4. A class implementing the #call method explicitly
5. A test-specific lambda

036 Blocks, Procs, and Lambdas

★

greeter = Proc.new do |name|
greeter_p = proc do |name|
greeter_l = lambda do |name|

argumentの扱いが微妙に違う

returnがあって、最後のコードが実行されない

p = proc do
  puts "In proc"
  return
  puts "After return"
end

l.call
p.call

puts "End of method"

"stabby lambda"

->(name) {

037 Proc and Threequals

★

threequals operator

You can match regular expressions, ranges, even classes with it

/\A\d+\z/ === "54321" # => true
(0..10) === 5         # => true
Numeric === 123       # => true

Procの===

even = ->(x){ (x % 2) == 0 }
even.call(2)                    # => true
even.call(3)                    # => false

even === 2                      # => true
even === 3                      # => false

caseで使われる

038 Caller-Specified Fallback

？

rescue => error
  if block_given?
    yield(error)
  else
    raise
  end
end