RubyのProcクラスとProc.newメソッドの使用法

var = 1
$foo = Proc.new { var }
var = 2

def foo
 $foo.call
end

p foo # => 2

def foo
 proc { return }
end

foo.call
# => in `call': return from proc-closure (LocalJumpError)

def foo
 proc { retry }
end

foo.call
# => in `call': retry from proc-closure (LocalJumpError)

# No problem.
(1..5).each { break }

# No problem in ruby 1.6.7, 1.8. In 1.6.8, an exception occurs
proc = Proc.new { break }
(1..5).each(&proc)

# LocalJumpError in ruby 1.6
# In ruby 1.8, run each again
proc = Proc.new { retry }
(1..5).each(&proc)
#=> retry from proc-closure (LocalJumpError)

Proc.new
Proc.new { ... }

def foo
  pr = Proc.new
  pr.call(1,2,3)
end
foo {|args| p args }
# => [1, 2, 3]

def foo
  pr = Proc.new
  pr.call(1,2,3)
end
foo {|args| p args }
# => [1, 2, 3]
This is the same as the following example
def foo
 yield(1,2,3)
end
foo {|args| p args }
# => [1, 2, 3]

def foo
 Proc.new
end
foo
# => -:2:in `new': tried to create Proc object without a block (ArgumentError)
     from -:2:in `foo'
     from -:4

# Processing to determine if a year in the Western calendar is a leap year
leap = Proc.new do |year|
 year % 4 == 0 && year % 100 ! = 0 || year % 400 == 0
end
　
p leap.call(2000) #=> true
p leap[2013] #=> false
p leap[2016] #=> true

double = Proc.new do |*args|
 args.map{|i| i * 2 } # multiply all elements twice
end
　
p double.call(1, 2, 3) #=> [2, 3, 4]
p double[2, 3, 4] #=> [4, 6, 8]