ruby 来自https://stackoverflow.com/questions/4817266/if-string-is-empty-then-return-some-default-value

Posted 2021-05-15

def hello
  yield name: 'Kasper'
end

hello { |options| p options[:name] }
# Outputs "Kasper"

Or named yielded arguments:

hello { |name:| p name }
# Outputs "Kasper"

Use an anonymous splat to avoid ArgumentErrors.

def hello
  yield name: 'Kasper', play_style: :laces_out
end

hello { |name:, **| p name }
# Outputs "Kasper"

Source: https://dev.firmafon.dk/blog/drat-ruby-has-a-double-splat/

t = DateTime.now
t.to_date + (t.min < 30 ? t.hour.hours : t.hour.hours + 30.minutes)

s = StringIO.open do |s|
  s.puts 'adding newlines with puts is easy...'
  s.puts 'and simple'
  s.string
end

def splitBase64(uri)
  if uri.match(%r{^data:(.*?);(.*?),(.*)$})
    return {
      type:      $1, # "image/png"
      encoder:   $2, # "base64"
      data:      $3, # data string
      extension: $1.split('/')[1] # "png"
      }
  end
end

class Dog
  def self.closest_relative
    "wolf"
  end
end

class Dog
  class << self
    def closest_relative
      "wolf"
    end
  end
end

def Dog.closest_relative
  "wolf"
end

class << Dog
  def closest_relative
    "wolf"
  end
end

def define_methods
  shared = 0
  Kernel.send(:define_method, :counter) { shared }
  Kernel.send(:define_method, :inc) { |x| shared += x }
end

# Delegate private methods
private *delegate(:foo, :bar, :to => :baz)

# Require all files from dir
Dir["/path/to/directory/*.rb"].each {|file| require file }

(0...10).map{ ('a'..'z').to_a[rand(26)] }.join

def pascal_triangle n
  next_row = ->(row) { ([0] + row).zip(row + [0]).map {|l,r| l + r} }
  row = ->(n) { n.times.inject([1]) {|x| next_row[x]} }
  n.times { |t| p row[t] }
end

def pascal_tr n
  row = Enumerator.new { |y, row=[1]| loop { y << row; row = ([0]+row).zip(row+[0]).map { |l,r| l+r } } }
  n.times { p row.next }
end

[ ] [ ]=    Element reference, element set
**  Exponentiation
! ~ + -     Not, complement, unary plus and minus (method names for the last two are +@ and -@)
* / %   Multiply, divide, and modulo
+ -     Plus and minus
>> <<   Right and left shift
&   Bitwise `and'
^ |     Bitwise exclusive `or' and regular `or'
<= < > >=   Comparison operators
<=> == === != =~ !~     Equality and pattern match operators (!= and !~ may not be defined as methods)

# Default string
class String
  def |(what)
    self.strip.blank? ? what : self
  end
end

@user.address | "We don't know user's address"


# Custom Splat
class Netrc
  Entry = Struct.new(:login, :password) do
    alias_method :to_ary, :to_a
  end
end

e = Netrc::Entry.new("user", "qwerty")
e.login # => "user"
e[:password] # => "qwerty"
e[1] # => "qwerty"
login, password = e

h = { foo: 1, bar: 2, baz: 3 }

# instead of this:
[:foo, :bar].map { |key| h[key] } #=> [1, 2]

# we can use this syntax:
[:foo, :bar].map(&h) #=> [1, 2]

class Point
  attr_accessor :x, :y
  def initialize(x, y)
    @x = x
    @y = y
    freeze
  end

  def change
    @x = 3
  end
end

point = Point.new(1,2)
point.change # RuntimeError: can't modify frozen Point

def fix_minutes
  until (0...60).member? minutes
    @hours -= 60 <=> minutes
    @minutes += 60 * (60 <=> minutes)
  end
  @hours %= 24
  self
end

def repeatedly
  Enumerator.new { |a| loop { a << yield } }  
end  

repeatedly {rand 100}.take 5

squares = ->() { Enumerator.new {|y, a=1| loop { y << a**2; a+=1 } }.lazy }
squares[].select { |e| e % 3 == 0 }.first 10

class Callable
  class << self
    extend Forwardable
    def_delegator :new, :call
  end

  def call
  end
end

Callable.call == Callable.new.call

dates = ->(p) { Enumerator.new { |y, n = 0| loop { y << Time.now.utc.beginning_of_day + n.days; n += p } } }

rows = [['one','two','three'],[1,2,3],[4,5,6]]

sv_str = rows.inject([]) { |csv, row|  csv << CSV.generate_line(row) }.join("")

File.open("orgs.csv", "w") {|f| f.write(rows.inject([]) { |csv, row|  csv << CSV.generate_line(row) }.join(""))}

# Ruby < 2.5 (https://blog.bigbinary.com/2017/10/18/ruby-2.5-has-removed-top-level-constant-lookup.html)

module Kernel
  A = B = C = D = E = F = "from kernel"
end
 
A = B = C = D = E = "from toplevel"
 
class Super
  A = B = C = D = "from superclass"
end
 
module Included
  A = B = C = "from included module"
end
 
module Enclosing
  A = B = "from enclosing module"
 
  class Local < Super
    include Included
 
    A = "defined locally"
 
    puts A  # "defined locally"
    puts B  # "from enclosing module"
    puts C  # "from included module"
    puts D  # "from superclass"
    puts E  # "from toplevel"
    puts F  # "from kernel"
  end
end

class Foo
  CONST_1 = 1
  CONST_2 = 2

  class_eval do
   constants.each { |c| define_method(c.downcase) { self.class.const_get c } }
  end
end

class Class
  def new(*args, &block)
    obj = allocate

    obj.initialize(*args, &block)
    # actually, this is obj.send(:initialize, …) because initialize is private

    obj
  end
end